Microbiology recall practice
Enable JavaScript for study mode, exam mode, section filters and question navigation. The source recall content is listed below. Q123 and Q158 are unscored source holds.
Q1. A patient develops indurated cervicofacial swelling and draining sinuses containing sulphur granules after dental disease. Which organism is most likely?
Recall paper: May 2024; Microbiology
A. Actinomyces israelii
B. Nocardia asteroides
C. Histoplasma capsulatum
D. Staphylococcus aureus
Answer and explanation
A. Actinomyces israelii
Actinomyces is a branching, filamentous, Gram-positive anaerobic bacterium that causes chronic invasive actinomycosis. Sulphur granules are bacterial colonies and are particularly characteristic in dental and cervicofacial disease.
B. Nocardia asteroides: Nocardia asteroides is an aerobic branching, weakly acid-fast bacterium more often affecting lungs, CNS or skin.
C. Histoplasma capsulatum: Histoplasma capsulatum is a dimorphic fungus often acquired from contaminated soil or bird/bat-dropping exposure.
D. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
Exam pearl: Actinomyces israelii — Nocardia is typically aerobic and weakly acid-fast
Q2. An inpatient develops profuse diarrhoea and colonic pseudomembranes after antimicrobial treatment. Which pathogen is responsible?
Recall paper: May 2024; Microbiology
A. Campylobacter jejuni
B. Shigella dysenteriae
C. Clostridioides difficile
D. Clostridium perfringens
Answer and explanation
C. Clostridioides difficile
Antibiotic disruption of the gut microbiota permits toxin-producing C. difficile proliferation. Toxins A and B produce epithelial injury, inflammation and pseudomembranous colitis.
A. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
B. Shigella dysenteriae: Shigella dysenteriae causes invasive bacillary dysentery and can produce Shiga toxin.
D. Clostridium perfringens: Clostridium perfringens is associated with clostridial myonecrosis, not this organism-specific diagnosis.
Exam pearl: Clostridioides difficile — Do not treat a positive colonisation test without compatible clinical illness.
Q3. A child develops a tender regional lymph node after a cat scratch. What is the likely bacterium?
Recall paper: January 2025; Microbiology
A. Pasteurella multocida
B. Eikenella corrodens
C. Bartonella henselae
D. Francisella tularensis
Answer and explanation
C. Bartonella henselae
Bartonella henselae is transmitted through cat-associated exposure and causes regional lymphadenitis, sometimes with an inoculation papule. Uncomplicated disease is usually self-limiting.
A. Pasteurella multocida: Pasteurella multocida is associated with rapidly progressive animal-bite infection, especially cat bites.
B. Eikenella corrodens: Eikenella corrodens is associated with human-bite infections and HACEK infections rather than this scenario.
D. Francisella tularensis: Francisella tularensis causes tularaemia after tick or animal exposure, often with ulceroglandular disease.
Exam pearl: Bartonella henselae — Differentiate cat-scratch lymphadenopathy from rapidly progressive infected cat bites.
Q4. Several patients acquire MRSA in the same surgical ward. What is its major route of transmission?
Recall paper: September 2016; Microbiology
A. Airborne transmission
B. Mosquito transmission
C. Waterborne transmission
D. Contact through hands or contaminated surfaces
Answer and explanation
D. Contact through hands or contaminated surfaces
MRSA is predominantly spread by direct or indirect contact, particularly contaminated healthcare workers’ hands or equipment. Appropriate hand hygiene, environmental cleaning and contact precautions reduce spread.
A. Airborne transmission: The relevant infection is not mainly spread through inhalation of an airborne agent; the exposure pathway in the question differs.
B. Mosquito transmission: This is a different vector or environmental exposure pathway and is not the transmission mechanism described.
C. Waterborne transmission: This is a different vector or environmental exposure pathway and is not the transmission mechanism described.
Exam pearl: Contact through hands or contaminated surfaces — Contact precautions differ from airborne isolation.
Q5. A patient with a prosthetic cardiac valve develops indolent infective endocarditis. Which organism has a characteristic prosthetic-surface biofilm association?
Recall paper: September 2016; Microbiology
A. Streptococcus pyogenes
B. Vibrio cholerae
C. Bordetella pertussis
D. Staphylococcus epidermidis
Answer and explanation
D. Staphylococcus epidermidis
Coagulase-negative staphylococci, especially S. epidermidis, adhere to artificial material and form biofilms. This makes prosthetic-device infections more persistent and difficult to eradicate.
A. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
B. Vibrio cholerae: Vibrio cholerae causes profuse watery secretory diarrhoea rather than the syndrome specified.
C. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
Exam pearl: Staphylococcus epidermidis — The most likely organism depends on timing and clinical syndrome
Q6. A patient from a lymphatic-filariasis endemic region has a massive hydrocele and chyluria. What is the classic parasite?
Recall paper: September 2016; Microbiology
A. Schistosoma haematobium
B. Wuchereria bancrofti
C. Taenia solium
D. Enterobius vermicularis
Answer and explanation
B. Wuchereria bancrofti
W. bancrofti is a mosquito-borne nematode that inhabits lymphatic vessels. Lymphatic obstruction can produce hydrocele, lymphoedema and leakage of lymph into urine (chyluria).
A. Schistosoma haematobium: Schistosoma haematobium produces urinary schistosomiasis, haematuria and increased squamous bladder-cancer risk.
C. Taenia solium: Taenia solium causes intestinal taeniasis or cysticercosis, not the hallmark syndrome here.
D. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
Exam pearl: Wuchereria bancrofti — Chyluria signifies lymphatic–urinary communication, not simply blood in the urine.
Q7. How should a flexible endoscope that contacts intact gastrointestinal mucosa be reprocessed at minimum?
Recall paper: January 2017; Microbiology
A. Brief alcohol wiping alone
B. Low-level disinfection
C. Thorough cleaning followed by high-level disinfection
D. Routine dry-heat sterilisation regardless of instrument compatibility
Answer and explanation
C. Thorough cleaning followed by high-level disinfection
Flexible GI endoscopes are Spaulding semicritical devices because they contact mucosa without normally entering sterile tissue. They require meticulous channel cleaning and at least high-level disinfection according to validated manufacturer instructions.
A. Brief alcohol wiping alone: Cleaning or low-level surface treatment alone is not a validated substitute for the required level of medical-device reprocessing.
B. Low-level disinfection: Low-level disinfection is reserved for noncritical equipment contacting intact skin, not semicritical or critical devices.
D. Routine dry-heat sterilisation regardless of instrument compatibility: The proposed reprocessing choice ignores the equipment classification or heat sensitivity; use an appropriate validated method.
Exam pearl: Thorough cleaning followed by high-level disinfection — A specific chemical named in a historical recall is not universally the “best” method
Q8. Which antibiotic class is conventionally used for selected post-splenectomy antibacterial prophylaxis?
Recall paper: January 2017; Microbiology
A. Penicillin-class prophylaxis
B. Aminoglycoside monotherapy
C. Routine quinolone monotherapy
D. Metronidazole monotherapy
Answer and explanation
A. Penicillin-class prophylaxis
Penicillin V or equivalent is commonly used according to age, risk and local asplenia protocols to reduce invasive pneumococcal infection risk. Vaccination, fever education and access to urgent treatment are equally important.
B. Aminoglycoside monotherapy: An aminoglycoside alone is not suitable prophylaxis for pneumococcal infection in asplenia.
C. Routine quinolone monotherapy: Routine quinolone monotherapy has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
D. Metronidazole monotherapy: Metronidazole monotherapy has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
Exam pearl: Penicillin-class prophylaxis — Do not treat penicillin prophylaxis as lifelong mandatory for every patient without assessing the applicable protocol.
Q9. Several patients acquire MRSA in the same surgical ward. What is its major route of transmission?
Recall paper: April 2017; Microbiology
A. Airborne transmission
B. Mosquito transmission
C. Contact through hands or contaminated surfaces
D. Waterborne transmission
Answer and explanation
C. Contact through hands or contaminated surfaces
MRSA is predominantly spread by direct or indirect contact, particularly contaminated healthcare workers’ hands or equipment. Appropriate hand hygiene, environmental cleaning and contact precautions reduce spread.
A. Airborne transmission: The relevant infection is not mainly spread through inhalation of an airborne agent; the exposure pathway in the question differs.
B. Mosquito transmission: This is a different vector or environmental exposure pathway and is not the transmission mechanism described.
D. Waterborne transmission: This is a different vector or environmental exposure pathway and is not the transmission mechanism described.
Exam pearl: Contact through hands or contaminated surfaces — Contact precautions differ from airborne isolation.
Q10. A recent traveller develops crampy bloody diarrhoea; investigation supports invasive amoebic colitis. What organism is responsible?
Recall paper: April 2017; Microbiology
A. Entamoeba histolytica
B. Campylobacter jejuni
C. Enterobius vermicularis
D. Hepatitis A virus
Answer and explanation
A. Entamoeba histolytica
Entamoeba histolytica invades colonic mucosa and can cause bloody diarrhoea, flask-shaped ulcers and extraintestinal liver abscess. Specific stool antigen or molecular testing is more discriminatory than cyst microscopy alone.
B. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
C. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
D. Hepatitis A virus: Hepatitis A virus causes faecal–oral acute hepatitis rather than this bacterial or parasitic disease.
Exam pearl: Entamoeba histolytica — Bloody diarrhoea after travel alone is not diagnostic of amoebiasis
Q11. A patient develops fever, abdominal pain and bloody diarrhoea after undercooked poultry. Which pathogen is classically involved?
Recall paper: April 2017; Microbiology
A. Staphylococcus aureus
B. Clostridioides difficile
C. Bordetella pertussis
D. Campylobacter jejuni
Answer and explanation
D. Campylobacter jejuni
Campylobacter jejuni is a curved, motile, Gram-negative organism transmitted especially through contaminated poultry. It causes inflammatory gastroenteritis and can cause ileocolitis resembling an acute surgical abdomen.
A. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
B. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
C. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
Exam pearl: Campylobacter jejuni — Campylobacter is a curved bacillus, not a flagellated diplococcus as one corrupted recall claims.
Q12. Tender ascending red streaks develop from a recent skin puncture. What is the classic pathogen?
Recall paper: April 2017; Microbiology
A. Streptococcus pyogenes
B. Staphylococcus epidermidis
C. Escherichia coli
D. Sporothrix schenckii
Answer and explanation
A. Streptococcus pyogenes
Group A beta-haemolytic streptococci commonly cause rapidly advancing nonpurulent cellulitis and lymphangitis. The tender proximal erythematous streaks reflect inflammation of superficial lymphatic vessels.
B. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
C. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
D. Sporothrix schenckii: Sporothrix causes delayed nodular lymphangitis following plant inoculation, rather than an acute red streak within 24–48 hours.
Exam pearl: Streptococcus pyogenes — Plant-thorn history alone does not prove sporotrichosis
Q13. A long-term ventilated ICU patient develops a hospital-acquired Gram-negative pneumonia. Which classic opportunistic organism should be considered?
Recall paper: April 2017; Microbiology
A. Streptococcus pneumoniae
B. Pseudomonas aeruginosa
C. Salmonella Typhi
D. Enterobius vermicularis
Answer and explanation
B. Pseudomonas aeruginosa
P. aeruginosa is an important pathogen in ventilator-associated pneumonia and other healthcare-associated infections. However, S. aureus and Enterobacterales are also common, so microbiology and local susceptibility data guide therapy.
A. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
C. Salmonella Typhi: Salmonella Typhi causes enteric fever, generally a systemic febrile illness rather than the condition in this stem.
D. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
Exam pearl: Pseudomonas aeruginosa — The wording “the main organism” is overly absolute
Q14. A child has nocturnal pruritus ani and a positive perianal adhesive-tape test. What is an appropriate antiparasitic treatment?
Recall paper: April 2017; Microbiology
A. Metronidazole
B. Mebendazole
C. Vancomycin
D. Tinidazole
Answer and explanation
B. Mebendazole
Mebendazole treats Enterobius vermicularis (pinworm), whose eggs are laid around the anus at night. A repeat dose after about two weeks and simultaneous household hygiene measures help prevent reinfection.
A. Metronidazole: Metronidazole is active against many anaerobic bacteria and protozoa, but the exact indication or route differs in this stem.
C. Vancomycin: Vancomycin is a glycopeptide used systemically against serious susceptible Gram-positive infections and orally for C. difficile.
D. Tinidazole: Tinidazole is a nitroimidazole used against certain anaerobic and protozoal infections, but not the preferred answer to this precise question.
Exam pearl: Mebendazole — The tape test and nocturnal pruritus point to pinworm, not amoebic dysentery.
Q15. A patient has a perforated colonic diverticulum with localised intra-abdominal abscess. Which microbial pattern is expected?
Recall paper: April 2017; Microbiology
A. Mixed enteric Gram-negative bacilli and anaerobes
B. Staphylococcus epidermidis alone
C. Neisseria meningitidis alone
D. Bordetella pertussis alone
Answer and explanation
A. Mixed enteric Gram-negative bacilli and anaerobes
Perforation of the colon releases polymicrobial bowel flora, including Enterobacterales such as E. coli and anaerobes such as Bacteroides. Source control and appropriately broad antimicrobial cover are required when indicated.
B. Staphylococcus epidermidis alone: Coagulase-negative staphylococci can infect devices, but this clinical syndrome cannot be assumed to arise from that organism alone.
C. Neisseria meningitidis alone: Meningococcus causes invasive sepsis/meningitis; this clinical syndrome generally requires a different or broader microbial explanation.
D. Bordetella pertussis alone: A single respiratory pathogen cannot account for an infection that is usually polymicrobial or involves a different tissue.
Exam pearl: Mixed enteric Gram-negative bacilli and anaerobes — Do not force one organism when a perforated colonic source is typically polymicrobial.
Q16. A recent traveller develops crampy bloody diarrhoea; investigation supports invasive amoebic colitis. What organism is responsible?
Recall paper: September 2017; Microbiology
A. Campylobacter jejuni
B. Enterobius vermicularis
C. Entamoeba histolytica
D. Hepatitis A virus
Answer and explanation
C. Entamoeba histolytica
Entamoeba histolytica invades colonic mucosa and can cause bloody diarrhoea, flask-shaped ulcers and extraintestinal liver abscess. Specific stool antigen or molecular testing is more discriminatory than cyst microscopy alone.
A. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
B. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
D. Hepatitis A virus: Hepatitis A virus causes faecal–oral acute hepatitis rather than this bacterial or parasitic disease.
Exam pearl: Entamoeba histolytica — Bloody diarrhoea after travel alone is not diagnostic of amoebiasis
Q17. A patient develops fever, abdominal pain and bloody diarrhoea after undercooked poultry. Which pathogen is classically involved?
Recall paper: September 2017; Microbiology
A. Staphylococcus aureus
B. Clostridioides difficile
C. Bordetella pertussis
D. Campylobacter jejuni
Answer and explanation
D. Campylobacter jejuni
Campylobacter jejuni is a curved, motile, Gram-negative organism transmitted especially through contaminated poultry. It causes inflammatory gastroenteritis and can cause ileocolitis resembling an acute surgical abdomen.
A. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
B. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
C. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
Exam pearl: Campylobacter jejuni — Campylobacter is a curved bacillus, not a flagellated diplococcus as one corrupted recall claims.
Q18. An adult has symptomatic non-fulminant C. difficile infection after clindamycin. What is an accepted targeted oral treatment?
Recall paper: September 2017; Microbiology
A. Intravenous vancomycin alone
B. Routine oral amoxicillin
C. Intravenous gentamicin
D. Oral vancomycin
Answer and explanation
D. Oral vancomycin
Oral vancomycin reaches high intraluminal colonic concentrations and is effective for C. difficile colitis. Current guidelines favour fidaxomicin where feasible, but oral vancomycin remains an accepted alternative.
A. Intravenous vancomycin alone: Intravenous vancomycin alone has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
B. Routine oral amoxicillin: Oral amoxicillin has restricted coverage for some Gram-negative or beta-lactamase-producing pathogens and may not fit this syndrome.
C. Intravenous gentamicin: Intravenous gentamicin has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
Exam pearl: Oral vancomycin — IV vancomycin alone does not adequately treat colonic C. difficile infection.
Q19. Four days after cholecystectomy a patient develops acute colicky abdominal pain without a definite fever or jaundice. What is the most appropriate next step?
Recall paper: September 2017; Clinical Surgery
A. Evaluate clinically and with targeted blood tests and imaging for a postoperative complication
B. Diagnose bile-duct injury solely from the pain
C. Diagnose postoperative sepsis despite no supporting evidence
D. Call it a benign post-cholecystectomy syndrome without assessment
Answer and explanation
A. Evaluate clinically and with targeted blood tests and imaging for a postoperative complication
Postoperative abdominal pain can result from retained common bile duct stone, biliary leak, duct injury, bleeding, ileus or unrelated causes. The source does not provide enough information for a unique diagnosis.
B. Diagnose bile-duct injury solely from the pain: Duct injury may cause pain or bile leak, but biochemical and imaging evaluation is required to establish it.
C. Diagnose postoperative sepsis despite no supporting evidence: This omits necessary evaluation or infection control and does not address the clinical risk described.
D. Call it a benign post-cholecystectomy syndrome without assessment: This omits necessary evaluation or infection control and does not address the clinical risk described.
Exam pearl: Evaluate clinically and with targeted blood tests and imaging for a postoperative complication — Avoid forcing a specific diagnosis from nonspecific post-cholecystectomy pain.
Q20. Which imaging method is preferred to identify a pituitary adenoma causing biochemical acromegaly?
Recall paper: September 2017; Imaging
A. Plain lateral skull radiograph
B. Abdominal ultrasonography
C. Plain chest radiograph
D. Pituitary MRI
Answer and explanation
D. Pituitary MRI
After biochemical confirmation using IGF-1 and appropriate GH suppression testing, contrast-enhanced pituitary MRI is the principal anatomic investigation. It identifies adenoma dimensions and adjacent neurovascular relations.
A. Plain lateral skull radiograph: A skull radiograph cannot characterise an intrasellar lesion or reliably establish the aetiology of acromegaly.
B. Abdominal ultrasonography: Abdominal ultrasound cannot directly demonstrate the pituitary lesion causing excess growth hormone.
C. Plain chest radiograph: Chest radiography does not evaluate the pituitary gland or define a sellar mass.
Exam pearl: Pituitary MRI — Pituitary MRI localises disease
Q21. An organ transplant recipient develops pneumonia despite antibacterial therapy. Which statement best guides the infectious differential?
Recall paper: September 2017; Microbiology
A. Cytomegalovirus is necessarily the cause at every transplant time point
B. Timing after transplantation and immunosuppressive status help distinguish bacterial, viral and fungal infections
C. The transplant organ does not affect risk
D. Negative response to antibiotics proves a viral diagnosis
Answer and explanation
B. Timing after transplantation and immunosuppressive status help distinguish bacterial, viral and fungal infections
CMV pneumonitis is an important transplant infection, especially after the first month or when prophylaxis is stopped; early postoperative infections are often bacterial or donor/recipient derived. The original recall variants have discordant or missing postoperative timelines and cannot establish one pathogen from antibiotic nonresponse alone.
A. Cytomegalovirus is necessarily the cause at every transplant time point: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
C. The transplant organ does not affect risk: Heart, lung, kidney and other solid-organ transplants have different infection risks and immunosuppression regimens.
D. Negative response to antibiotics proves a viral diagnosis: Poor antibacterial response may reflect resistant bacteria, inadequate source control, fungal disease or a noninfectious diagnosis.
Exam pearl: Timing after transplantation and immunosuppressive status help distinguish bacterial, viral and fungal infections — Transplant pneumonia is time-dependent
Q22. An asymptomatic elective-surgery patient is found to carry MRSA in the nares. Which topical agent is commonly used for nasal decolonisation?
Recall paper: January 2018; Microbiology
A. Oral vancomycin
B. Intravenous metronidazole
C. Oral fluconazole
D. Intranasal mupirocin
Answer and explanation
D. Intranasal mupirocin
Mupirocin ointment applied intranasally is a common component of targeted MRSA decolonisation. Chlorhexidine washes are often added for skin decolonisation in accordance with local protocols.
A. Oral vancomycin: Oral vancomycin acts principally within the intestine because systemic absorption is poor; it does not treat bloodstream infection.
B. Intravenous metronidazole: Intravenous metronidazole is not equivalent to preferred oral luminal therapy for nonfulminant C. difficile disease.
C. Oral fluconazole: Fluconazole treats susceptible fungal infection; it is not an anti-MRSA decolonising drug or a luminal C. difficile agent.
Exam pearl: Intranasal mupirocin — Decolonisation is not the same as treating MRSA bacteraemia.
Q23. A postoperative patient with an asymptomatic Gram-positive blood culture is next to another patient with MRSA. What is the correct initial response?
Recall paper: January 2018; Microbiology
A. Treat all positive cultures with nasal mupirocin alone
B. Assess the blood culture significance and obtain organism identification
C. Assume nasal MRSA colonisation proves bloodstream infection
D. Ignore a confirmed Staphylococcus aureus blood culture
Answer and explanation
B. Assess the blood culture significance and obtain organism identification
A Gram-positive blood culture can indicate true bacteraemia or skin-flora contamination. Speciation, number of positive bottles, clinical condition and repeat cultures guide assessment; confirmed S. aureus bacteraemia requires prompt systemic management.
A. Treat all positive cultures with nasal mupirocin alone: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
C. Assume nasal MRSA colonisation proves bloodstream infection: Colonisation and positive blood cultures require separate microbiological confirmation and clinical interpretation.
D. Ignore a confirmed Staphylococcus aureus blood culture: This omits necessary evaluation or infection control and does not address the clinical risk described.
Exam pearl: Assess the blood culture significance and obtain organism identification — MRSA exposure does not establish which organism grew from a blood culture.
Q24. A patient has laboratory-supported invasive Entamoeba histolytica colitis with bloody diarrhoea. Which drug treats the invasive tissue stage?
Recall paper: January 2018; Microbiology
A. Mebendazole
B. Penicillin V
C. Vancomycin
D. Metronidazole
Answer and explanation
D. Metronidazole
Metronidazole treats invasive amoebic infection by acting on trophozoites in tissues. It must be followed by a luminal amoebicide where available to eradicate cyst carriage and prevent relapse.
A. Mebendazole: Mebendazole is an antihelminthic effective against intestinal nematodes such as pinworm, not the process in this question.
B. Penicillin V: Penicillin V may be used for asplenia prophylaxis or susceptible streptococci but not for this particular indication.
C. Vancomycin: Vancomycin is a glycopeptide used systemically against serious susceptible Gram-positive infections and orally for C. difficile.
Exam pearl: Metronidazole — Metronidazole alone does not reliably eliminate intestinal luminal cysts.
Q25. An organ transplant recipient develops pneumonia despite antibacterial therapy. Which statement best guides the infectious differential?
Recall paper: January 2018; Microbiology
A. Timing after transplantation and immunosuppressive status help distinguish bacterial, viral and fungal infections
B. Cytomegalovirus is necessarily the cause at every transplant time point
C. The transplant organ does not affect risk
D. Negative response to antibiotics proves a viral diagnosis
Answer and explanation
A. Timing after transplantation and immunosuppressive status help distinguish bacterial, viral and fungal infections
CMV pneumonitis is an important transplant infection, especially after the first month or when prophylaxis is stopped; early postoperative infections are often bacterial or donor/recipient derived. The original recall variants have discordant or missing postoperative timelines and cannot establish one pathogen from antibiotic nonresponse alone.
B. Cytomegalovirus is necessarily the cause at every transplant time point: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
C. The transplant organ does not affect risk: Heart, lung, kidney and other solid-organ transplants have different infection risks and immunosuppression regimens.
D. Negative response to antibiotics proves a viral diagnosis: Poor antibacterial response may reflect resistant bacteria, inadequate source control, fungal disease or a noninfectious diagnosis.
Exam pearl: Timing after transplantation and immunosuppressive status help distinguish bacterial, viral and fungal infections — Transplant pneumonia is time-dependent
Q26. A sexually active young man has fever, dysuria, urethral discharge and gradual unilateral epididymal pain. Which organism is a common cause?
Recall paper: April 2018; Microbiology
A. Escherichia coli
B. Chlamydia trachomatis
C. Staphylococcus epidermidis
D. Mumps virus
Answer and explanation
B. Chlamydia trachomatis
C. trachomatis is a frequent cause of epididymitis in younger sexually active men, often with associated urethritis. Gonorrhoea is another important STI cause; testing and empirical treatment should address relevant pathogens.
A. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
C. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Mumps virus: Mumps can cause viral orchitis, usually associated with parotitis, rather than typical sexually transmitted urethritis with discharge.
Exam pearl: Chlamydia trachomatis — Never allow a presumed diagnosis of epididymitis to delay evaluation of possible testicular torsion.
Q27. An elderly patient has an MRSA-positive swab from a chronic venous ulcer but no cellulitis, fever or other infection signs. What is the appropriate antibiotic decision?
Recall paper: April 2018; Microbiology
A. No systemic antibiotics for colonisation alone
B. Intravenous vancomycin automatically
C. Oral metronidazole automatically
D. Routine intramuscular gentamicin
Answer and explanation
A. No systemic antibiotics for colonisation alone
A positive superficial swab often represents colonisation rather than clinically relevant tissue infection. In the absence of infection, systemic antibiotics add toxicity and resistance without reliably improving ulcer healing.
B. Intravenous vancomycin automatically: Intravenous vancomycin automatically has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
C. Oral metronidazole automatically: Oral metronidazole automatically has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
D. Routine intramuscular gentamicin: Routine intramuscular gentamicin has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
Exam pearl: No systemic antibiotics for colonisation alone — Culture positivity is not equivalent to infection.
Q28. A returning traveller has vomiting and nonspecific abdominal pain with no fever, stool pattern or exposure history supplied. What is the most defensible conclusion?
Recall paper: September 2018; Microbiology
A. Typhoid fever is proven by travel alone
B. The pathogen cannot be inferred without further symptoms and exposure history
C. Hepatitis A is proven by abdominal pain alone
D. Staphylococcal food poisoning is proven regardless of incubation
Answer and explanation
B. The pathogen cannot be inferred without further symptoms and exposure history
Typhoid, viral hepatitis and foodborne intoxication can all cause gastrointestinal symptoms in returning travellers; chronology, fever, jaundice, diarrhoea pattern and exposures distinguish them. The source stem is insufficient for a microbiological diagnosis.
A. Typhoid fever is proven by travel alone: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
C. Hepatitis A is proven by abdominal pain alone: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
D. Staphylococcal food poisoning is proven regardless of incubation: Preformed toxin typically has a very short incubation, and pathogen identification cannot be inferred without relevant timing.
Exam pearl: The pathogen cannot be inferred without further symptoms and exposure history — Geographical travel alone cannot determine an organism.
Q29. A livestock-associated painless ulcer develops a characteristic black eschar and extensive oedema. Which organism should be suspected?
Recall paper: September 2018; Microbiology
A. Bacillus anthracis
B. Streptococcus pyogenes
C. Staphylococcus aureus
D. Clostridium difficile
Answer and explanation
A. Bacillus anthracis
Cutaneous anthrax may begin as a papule and progress to a painless ulcer with black eschar, sometimes with substantial surrounding oedema. B. anthracis is a spore-forming Gram-positive bacillus.
B. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
C. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
D. Clostridium difficile: Clostridium difficile is the former name of C. difficile, a cause of antibiotic-associated colitis rather than this presentation.
Exam pearl: Bacillus anthracis — Characteristic painless eschar and animal exposure matter more than eschar colour alone.
Q30. A contaminated traumatic wound rapidly develops malodour, gas and extensive muscle necrosis. What is the essential management principle?
Recall paper: September 2018; Microbiology
A. Topical antiseptic alone
B. Urgent surgical debridement plus broad-spectrum antibiotics
C. Delay surgery until all cultures return
D. Oral doxycycline monotherapy
Answer and explanation
B. Urgent surgical debridement plus broad-spectrum antibiotics
Clostridial myonecrosis and necrotising wound infection are surgical emergencies requiring immediate exploration and radical debridement. Empirical antimicrobials must cover Gram-positive, Gram-negative and anaerobic organisms, then be refined by cultures; targeted clostridial therapy usually includes penicillin plus clindamycin.
A. Topical antiseptic alone: Surface antisepsis cannot provide definitive therapy for deep established infection or replace necessary systemic therapy and source control.
C. Delay surgery until all cultures return: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
D. Oral doxycycline monotherapy: Doxycycline alone may lack the anaerobic or Gram-negative breadth necessary for necrotising or mixed traumatic infection.
Exam pearl: Urgent surgical debridement plus broad-spectrum antibiotics — No antibiotic substitutes for prompt surgical source control.
Q31. An asymptomatic elective-surgery patient is found to carry MRSA in the nares. Which topical agent is commonly used for nasal decolonisation?
Recall paper: September 2018; Microbiology
A. Intranasal mupirocin
B. Oral vancomycin
C. Intravenous metronidazole
D. Oral fluconazole
Answer and explanation
A. Intranasal mupirocin
Mupirocin ointment applied intranasally is a common component of targeted MRSA decolonisation. Chlorhexidine washes are often added for skin decolonisation in accordance with local protocols.
B. Oral vancomycin: Oral vancomycin acts principally within the intestine because systemic absorption is poor; it does not treat bloodstream infection.
C. Intravenous metronidazole: Intravenous metronidazole is not equivalent to preferred oral luminal therapy for nonfulminant C. difficile disease.
D. Oral fluconazole: Fluconazole treats susceptible fungal infection; it is not an anti-MRSA decolonising drug or a luminal C. difficile agent.
Exam pearl: Intranasal mupirocin — Decolonisation is not the same as treating MRSA bacteraemia.
Q32. An adult has persistent generalised lymphadenopathy and relevant exposure risk. Which viral infection belongs prominently in the differential?
Recall paper: September 2018; Microbiology
A. Hepatitis A infection
B. Rhinovirus infection
C. Varicella-zoster reactivation
D. HIV infection
Answer and explanation
D. HIV infection
HIV can produce persistent generalised lymphadenopathy during early or chronic stages. Confirm with a validated HIV antigen/antibody algorithm rather than relying on lymph node enlargement alone.
A. Hepatitis A infection: Hepatitis A infection concerns a different cell, inflammatory mechanism or immune component from the one directly implicated here.
B. Rhinovirus infection: Rhinovirus usually causes common-cold symptoms rather than transplant CMV disease or a specified oncogenic syndrome.
C. Varicella-zoster reactivation: VZV reactivation classically causes shingles, not the hallmark condition in this vignette.
Exam pearl: HIV infection — This source stem is truncated
Q33. A postoperative patient with an asymptomatic Gram-positive blood culture is next to another patient with MRSA. What is the correct initial response?
Recall paper: January 2019; Microbiology
A. Assess the blood culture significance and obtain organism identification
B. Treat all positive cultures with nasal mupirocin alone
C. Assume nasal MRSA colonisation proves bloodstream infection
D. Ignore a confirmed Staphylococcus aureus blood culture
Answer and explanation
A. Assess the blood culture significance and obtain organism identification
A Gram-positive blood culture can indicate true bacteraemia or skin-flora contamination. Speciation, number of positive bottles, clinical condition and repeat cultures guide assessment; confirmed S. aureus bacteraemia requires prompt systemic management.
B. Treat all positive cultures with nasal mupirocin alone: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
C. Assume nasal MRSA colonisation proves bloodstream infection: Colonisation and positive blood cultures require separate microbiological confirmation and clinical interpretation.
D. Ignore a confirmed Staphylococcus aureus blood culture: This omits necessary evaluation or infection control and does not address the clinical risk described.
Exam pearl: Assess the blood culture significance and obtain organism identification — MRSA exposure does not establish which organism grew from a blood culture.
Q34. An organ transplant recipient develops pneumonia despite antibacterial therapy. Which statement best guides the infectious differential?
Recall paper: January 2019; Microbiology
A. Cytomegalovirus is necessarily the cause at every transplant time point
B. The transplant organ does not affect risk
C. Negative response to antibiotics proves a viral diagnosis
D. Timing after transplantation and immunosuppressive status help distinguish bacterial, viral and fungal infections
Answer and explanation
D. Timing after transplantation and immunosuppressive status help distinguish bacterial, viral and fungal infections
CMV pneumonitis is an important transplant infection, especially after the first month or when prophylaxis is stopped; early postoperative infections are often bacterial or donor/recipient derived. The original recall variants have discordant or missing postoperative timelines and cannot establish one pathogen from antibiotic nonresponse alone.
A. Cytomegalovirus is necessarily the cause at every transplant time point: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
B. The transplant organ does not affect risk: Heart, lung, kidney and other solid-organ transplants have different infection risks and immunosuppression regimens.
C. Negative response to antibiotics proves a viral diagnosis: Poor antibacterial response may reflect resistant bacteria, inadequate source control, fungal disease or a noninfectious diagnosis.
Exam pearl: Timing after transplantation and immunosuppressive status help distinguish bacterial, viral and fungal infections — Transplant pneumonia is time-dependent
Q35. An organ transplant recipient develops pneumonia despite antibacterial therapy. Which statement best guides the infectious differential?
Recall paper: January 2019; Microbiology
A. Cytomegalovirus is necessarily the cause at every transplant time point
B. The transplant organ does not affect risk
C. Negative response to antibiotics proves a viral diagnosis
D. Timing after transplantation and immunosuppressive status help distinguish bacterial, viral and fungal infections
Answer and explanation
D. Timing after transplantation and immunosuppressive status help distinguish bacterial, viral and fungal infections
CMV pneumonitis is an important transplant infection, especially after the first month or when prophylaxis is stopped; early postoperative infections are often bacterial or donor/recipient derived. The original recall variants have discordant or missing postoperative timelines and cannot establish one pathogen from antibiotic nonresponse alone.
A. Cytomegalovirus is necessarily the cause at every transplant time point: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
B. The transplant organ does not affect risk: Heart, lung, kidney and other solid-organ transplants have different infection risks and immunosuppression regimens.
C. Negative response to antibiotics proves a viral diagnosis: Poor antibacterial response may reflect resistant bacteria, inadequate source control, fungal disease or a noninfectious diagnosis.
Exam pearl: Timing after transplantation and immunosuppressive status help distinguish bacterial, viral and fungal infections — Transplant pneumonia is time-dependent
Q36. A postoperative patient with an asymptomatic Gram-positive blood culture is next to another patient with MRSA. What is the correct initial response?
Recall paper: January 2019; Microbiology
A. Treat all positive cultures with nasal mupirocin alone
B. Assess the blood culture significance and obtain organism identification
C. Assume nasal MRSA colonisation proves bloodstream infection
D. Ignore a confirmed Staphylococcus aureus blood culture
Answer and explanation
B. Assess the blood culture significance and obtain organism identification
A Gram-positive blood culture can indicate true bacteraemia or skin-flora contamination. Speciation, number of positive bottles, clinical condition and repeat cultures guide assessment; confirmed S. aureus bacteraemia requires prompt systemic management.
A. Treat all positive cultures with nasal mupirocin alone: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
C. Assume nasal MRSA colonisation proves bloodstream infection: Colonisation and positive blood cultures require separate microbiological confirmation and clinical interpretation.
D. Ignore a confirmed Staphylococcus aureus blood culture: This omits necessary evaluation or infection control and does not address the clinical risk described.
Exam pearl: Assess the blood culture significance and obtain organism identification — MRSA exposure does not establish which organism grew from a blood culture.
Q37. A healthcare worker has a contaminated needlestick injury. Which blood-borne virus has historically been highly transmissible from an infected source in the absence of immunity?
Recall paper: April 2019; Microbiology
A. Hepatitis C virus
B. Human immunodeficiency virus
C. Cytomegalovirus
D. Hepatitis B virus
Answer and explanation
D. Hepatitis B virus
Hepatitis B has a higher occupational percutaneous transmission risk than HIV, especially when the source is HBeAg positive and the exposed worker is nonimmune. The source wording “most commonly reported” is ambiguous and differs from asking about relative biological transmissibility.
A. Hepatitis C virus: Hepatitis C virus causes blood-borne chronic hepatitis and is not the organism associated with this particular presentation.
B. Human immunodeficiency virus: Human immunodeficiency virus causes immunodeficiency and secondary infections, not a single named bacterial infection.
C. Cytomegalovirus: Cytomegalovirus is an important viral opportunistic infection after transplantation, particularly with immune suppression.
Exam pearl: Hepatitis B virus — Distinguish highest biological transmission risk from observed incidence in a vaccinated workforce.
Q38. Which vaccine combination specifically targets major encapsulated bacteria in asplenic patients?
Recall paper: April 2019; Microbiology
A. BCG alone
B. Hepatitis A vaccine alone
C. Rotavirus vaccine alone
D. Pneumococcal, meningococcal and Hib vaccination
Answer and explanation
D. Pneumococcal, meningococcal and Hib vaccination
Splenectomy increases susceptibility to rapidly progressive infection by encapsulated pathogens, notably S. pneumoniae, N. meningitidis and H. influenzae type b. Vaccinate according to current age- and history-based schedules.
A. BCG alone: BCG protects primarily against severe tuberculosis in childhood and does not replace encapsulated-bacterium vaccines.
B. Hepatitis A vaccine alone: Hepatitis A vaccine alone concerns a different cell, inflammatory mechanism or immune component from the one directly implicated here.
C. Rotavirus vaccine alone: Rotavirus vaccination prevents selected gastroenteritis outcomes, not invasive pneumococcal or meningococcal disease.
Exam pearl: Pneumococcal, meningococcal and Hib vaccination — Vaccination lowers but does not eliminate overwhelming post-splenectomy infection risk.
Q39. How should a flexible endoscope that contacts intact gastrointestinal mucosa be reprocessed at minimum?
Recall paper: April 2019; Microbiology
A. Brief alcohol wiping alone
B. Low-level disinfection
C. Routine dry-heat sterilisation regardless of instrument compatibility
D. Thorough cleaning followed by high-level disinfection
Answer and explanation
D. Thorough cleaning followed by high-level disinfection
Flexible GI endoscopes are Spaulding semicritical devices because they contact mucosa without normally entering sterile tissue. They require meticulous channel cleaning and at least high-level disinfection according to validated manufacturer instructions.
A. Brief alcohol wiping alone: Cleaning or low-level surface treatment alone is not a validated substitute for the required level of medical-device reprocessing.
B. Low-level disinfection: Low-level disinfection is reserved for noncritical equipment contacting intact skin, not semicritical or critical devices.
C. Routine dry-heat sterilisation regardless of instrument compatibility: The proposed reprocessing choice ignores the equipment classification or heat sensitivity; use an appropriate validated method.
Exam pearl: Thorough cleaning followed by high-level disinfection — A specific chemical named in a historical recall is not universally the “best” method
Q40. An ulcer with undermined violaceous borders develops around an ileostomy in a patient with ulcerative colitis. Which condition is most likely?
Recall paper: April 2019; Pathology
A. Erythema nodosum
B. Pyoderma gangrenosum
C. Squamous cell carcinoma
D. Impetigo
Answer and explanation
B. Pyoderma gangrenosum
Pyoderma gangrenosum is a neutrophilic dermatosis associated with inflammatory bowel disease. Painful rapidly expanding ulcers may arise around a stoma and worsen after trauma (pathergy).
A. Erythema nodosum: Erythema nodosum is a different morphological finding and is not the distinctive clinical feature requested.
C. Squamous cell carcinoma: This epithelial malignancy has a different ulcerative or mass-forming course from the inflammatory lesion described.
D. Impetigo: Impetigo is a superficial crusting epidermal bacterial infection rather than a deep neutrophilic dermatosis or ulcerative process.
Exam pearl: Pyoderma gangrenosum — Despite the name, pyoderma gangrenosum is not primarily a bacterial infection.
Q41. An asymptomatic elective-surgery patient is found to carry MRSA in the nares. Which topical agent is commonly used for nasal decolonisation?
Recall paper: September 2019; Microbiology
A. Intranasal mupirocin
B. Oral vancomycin
C. Intravenous metronidazole
D. Oral fluconazole
Answer and explanation
A. Intranasal mupirocin
Mupirocin ointment applied intranasally is a common component of targeted MRSA decolonisation. Chlorhexidine washes are often added for skin decolonisation in accordance with local protocols.
B. Oral vancomycin: Oral vancomycin acts principally within the intestine because systemic absorption is poor; it does not treat bloodstream infection.
C. Intravenous metronidazole: Intravenous metronidazole is not equivalent to preferred oral luminal therapy for nonfulminant C. difficile disease.
D. Oral fluconazole: Fluconazole treats susceptible fungal infection; it is not an anti-MRSA decolonising drug or a luminal C. difficile agent.
Exam pearl: Intranasal mupirocin — Decolonisation is not the same as treating MRSA bacteraemia.
Q42. An adult has symptomatic non-fulminant C. difficile infection after clindamycin. What is an accepted targeted oral treatment?
Recall paper: September 2019; Microbiology
A. Intravenous vancomycin alone
B. Routine oral amoxicillin
C. Oral vancomycin
D. Intravenous gentamicin
Answer and explanation
C. Oral vancomycin
Oral vancomycin reaches high intraluminal colonic concentrations and is effective for C. difficile colitis. Current guidelines favour fidaxomicin where feasible, but oral vancomycin remains an accepted alternative.
A. Intravenous vancomycin alone: Intravenous vancomycin alone has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
B. Routine oral amoxicillin: Oral amoxicillin has restricted coverage for some Gram-negative or beta-lactamase-producing pathogens and may not fit this syndrome.
D. Intravenous gentamicin: Intravenous gentamicin has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
Exam pearl: Oral vancomycin — IV vancomycin alone does not adequately treat colonic C. difficile infection.
Q43. A traumatic wound develops clostridial myonecrosis with gas and rapid tissue destruction. Which organism is classic?
Recall paper: September 2019; Microbiology
A. Clostridioides difficile
B. Staphylococcus epidermidis
C. Neisseria gonorrhoeae
D. Clostridium perfringens
Answer and explanation
D. Clostridium perfringens
C. perfringens is an anaerobic Gram-positive spore-forming rod. Its alpha toxin (phospholipase C) causes muscle injury, haemolysis and severe toxemia in gas gangrene.
A. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
B. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
C. Neisseria gonorrhoeae: Neisseria gonorrhoeae causes sexually transmitted urethritis and sometimes epididymitis or disseminated arthritis.
Exam pearl: Clostridium perfringens — Toxin production explains why clostridial myonecrosis can progress extremely quickly.
Q44. Needle-shaped, strongly negatively birefringent crystals are seen in synovial fluid. What is the diagnosis?
Recall paper: January 2020; Pathology
A. Calcium pyrophosphate crystal arthritis
B. Septic arthritis
C. Rheumatoid arthritis
D. Monosodium urate crystal arthritis (gout)
Answer and explanation
D. Monosodium urate crystal arthritis (gout)
Monosodium urate forms needle-shaped negatively birefringent crystals under polarised light, supporting gout. Calcium pyrophosphate deposits form shorter rhomboid weakly positive birefringent crystals.
A. Calcium pyrophosphate crystal arthritis: Calcium pyrophosphate crystal arthritis is a different pathological or clinical diagnosis, with a pattern distinct from the defining findings in this stem.
B. Septic arthritis: Septic arthritis is a different pathological or clinical diagnosis, with a pattern distinct from the defining findings in this stem.
C. Rheumatoid arthritis: Rheumatoid arthritis is a different pathological or clinical diagnosis, with a pattern distinct from the defining findings in this stem.
Exam pearl: Monosodium urate crystal arthritis (gout) — Do not mistake gout crystals for pyrophosphate crystals.
Q45. A solid-organ transplant recipient in the intermediate post-transplant period develops unexplained pneumonitis and systemic symptoms. What opportunistic virus should be investigated?
Recall paper: January 2020; Microbiology
A. Epstein–Barr virus
B. Human papillomavirus
C. Hepatitis A virus
D. Cytomegalovirus
Answer and explanation
D. Cytomegalovirus
CMV can produce a viral syndrome and tissue-invasive disease including pneumonitis after transplantation. Risk is affected by donor/recipient serostatus, prophylaxis, immunosuppression and time since transplant.
A. Epstein–Barr virus: Epstein–Barr virus causes infectious mononucleosis and is linked to several lymphomas and nasopharyngeal carcinoma.
B. Human papillomavirus: Human papillomavirus causes epithelial papillomas and is associated with selected anogenital and oropharyngeal carcinomas.
C. Hepatitis A virus: Hepatitis A virus causes faecal–oral acute hepatitis rather than this bacterial or parasitic disease.
Exam pearl: Cytomegalovirus — A transplant patient’s pneumonia cannot be diagnosed as CMV from transplant status alone
Q46. How should a flexible endoscope that contacts intact gastrointestinal mucosa be reprocessed at minimum?
Recall paper: January 2020; Microbiology
A. Brief alcohol wiping alone
B. Thorough cleaning followed by high-level disinfection
C. Low-level disinfection
D. Routine dry-heat sterilisation regardless of instrument compatibility
Answer and explanation
B. Thorough cleaning followed by high-level disinfection
Flexible GI endoscopes are Spaulding semicritical devices because they contact mucosa without normally entering sterile tissue. They require meticulous channel cleaning and at least high-level disinfection according to validated manufacturer instructions.
A. Brief alcohol wiping alone: Cleaning or low-level surface treatment alone is not a validated substitute for the required level of medical-device reprocessing.
C. Low-level disinfection: Low-level disinfection is reserved for noncritical equipment contacting intact skin, not semicritical or critical devices.
D. Routine dry-heat sterilisation regardless of instrument compatibility: The proposed reprocessing choice ignores the equipment classification or heat sensitivity; use an appropriate validated method.
Exam pearl: Thorough cleaning followed by high-level disinfection — A specific chemical named in a historical recall is not universally the “best” method
Q47. An adult with HIV develops pneumonia but no CD4 count, imaging or microbiological findings are given. What is the best interpretation?
Recall paper: January 2020; Microbiology
A. All HIV-related pneumonia is due to Pneumocystis jirovecii
B. The specific pneumonia pathogen cannot be determined from HIV status alone
C. Aspergillus flavus is inevitably responsible
D. Pseudomonas aeruginosa is inevitably responsible
Answer and explanation
B. The specific pneumonia pathogen cannot be determined from HIV status alone
HIV increases risk of both ordinary community-acquired bacterial pneumonia and opportunistic infection, but the likely organism depends on CD4 count, prophylaxis, symptoms and radiology. The source recall lacks the discriminating clinical details needed to pick a single organism.
A. All HIV-related pneumonia is due to Pneumocystis jirovecii: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
C. Aspergillus flavus is inevitably responsible: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
D. Pseudomonas aeruginosa is inevitably responsible: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
Exam pearl: The specific pneumonia pathogen cannot be determined from HIV status alone — Do not equate HIV with an automatic diagnosis of pneumocystis.
Q48. A 12-year-old presents with fever and a painful restricted hip, concerning for acute septic arthritis. What organism is a common cause?
Recall paper: January 2020; Microbiology
A. Salmonella Typhi
B. Staphylococcus aureus
C. Pseudomonas aeruginosa
D. Clostridioides difficile
Answer and explanation
B. Staphylococcus aureus
Staphylococcus aureus is an important and frequent cause of paediatric septic arthritis. The original recall did not describe sickle-cell disease; therefore it must not be altered into the distinct Salmonella-in-sickle-cell association.
A. Salmonella Typhi: Salmonella Typhi causes enteric fever, generally a systemic febrile illness rather than the condition in this stem.
C. Pseudomonas aeruginosa: Pseudomonas aeruginosa is prominent in burns, catheter-related infection and healthcare-associated pneumonia, not the hallmark being asked.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Do not invent sickle-cell disease from a child presenting with a painful hip.
Q49. Which organism is the leading cause of uncomplicated community-acquired urinary tract infection?
Recall paper: January 2020; Microbiology
A. Proteus mirabilis
B. Pseudomonas aeruginosa
C. Staphylococcus epidermidis
D. Escherichia coli
Answer and explanation
D. Escherichia coli
Uropathogenic E. coli causes the majority of uncomplicated community-acquired UTIs because it adheres to uroepithelium using fimbrial adhesins and can ascend from periurethral flora.
A. Proteus mirabilis: Proteus mirabilis is urease-positive and particularly associated with infection stones, not every ordinary urinary infection.
B. Pseudomonas aeruginosa: Pseudomonas aeruginosa is prominent in burns, catheter-related infection and healthcare-associated pneumonia, not the hallmark being asked.
C. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
Exam pearl: Escherichia coli — Overall UTI leader: E. coli
Q50. An inpatient develops profuse diarrhoea and colonic pseudomembranes after antimicrobial treatment. Which pathogen is responsible?
Recall paper: September 2020; Microbiology
A. Campylobacter jejuni
B. Clostridioides difficile
C. Shigella dysenteriae
D. Clostridium perfringens
Answer and explanation
B. Clostridioides difficile
Antibiotic disruption of the gut microbiota permits toxin-producing C. difficile proliferation. Toxins A and B produce epithelial injury, inflammation and pseudomembranous colitis.
A. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
C. Shigella dysenteriae: Shigella dysenteriae causes invasive bacillary dysentery and can produce Shiga toxin.
D. Clostridium perfringens: Clostridium perfringens is associated with clostridial myonecrosis, not this organism-specific diagnosis.
Exam pearl: Clostridioides difficile — Do not treat a positive colonisation test without compatible clinical illness.
Q51. A patient from a lymphatic-filariasis endemic region has a massive hydrocele and chyluria. What is the classic parasite?
Recall paper: September 2020; Microbiology
A. Schistosoma haematobium
B. Wuchereria bancrofti
C. Taenia solium
D. Enterobius vermicularis
Answer and explanation
B. Wuchereria bancrofti
W. bancrofti is a mosquito-borne nematode that inhabits lymphatic vessels. Lymphatic obstruction can produce hydrocele, lymphoedema and leakage of lymph into urine (chyluria).
A. Schistosoma haematobium: Schistosoma haematobium produces urinary schistosomiasis, haematuria and increased squamous bladder-cancer risk.
C. Taenia solium: Taenia solium causes intestinal taeniasis or cysticercosis, not the hallmark syndrome here.
D. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
Exam pearl: Wuchereria bancrofti — Chyluria signifies lymphatic–urinary communication, not simply blood in the urine.
Q52. A patient has rapidly spreading perineal necrosis and systemic toxicity (Fournier gangrene). What microbiological pattern is classically associated?
Recall paper: September 2020; Microbiology
A. Only Candida albicans
B. Only Streptococcus pneumoniae
C. Only Mycobacterium tuberculosis
D. Polymicrobial aerobic and anaerobic flora
Answer and explanation
D. Polymicrobial aerobic and anaerobic flora
Fournier gangrene is a necrotising fasciitis of the genital and perineal fascial compartments, often caused by a synergy of enteric Gram-negative organisms, streptococci and anaerobes. Monomicrobial infection is possible but not the classic pattern.
A. Only Candida albicans: Candida alone is not the usual explanation for rapidly destructive mixed perineal bacterial infection.
B. Only Streptococcus pneumoniae: Pneumococcus is not the sole cause of necrotising perineal or intra-abdominal infection.
C. Only Mycobacterium tuberculosis: Tuberculosis is generally indolent and is not the classic sole cause of rapid polymicrobial soft-tissue necrosis.
Exam pearl: Polymicrobial aerobic and anaerobic flora — Clinical priority is operative source control, not obtaining a single-organism culture.
Q53. Tender ascending red streaks develop from a recent skin puncture. What is the classic pathogen?
Recall paper: September 2020; Microbiology
A. Staphylococcus epidermidis
B. Streptococcus pyogenes
C. Escherichia coli
D. Sporothrix schenckii
Answer and explanation
B. Streptococcus pyogenes
Group A beta-haemolytic streptococci commonly cause rapidly advancing nonpurulent cellulitis and lymphangitis. The tender proximal erythematous streaks reflect inflammation of superficial lymphatic vessels.
A. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
C. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
D. Sporothrix schenckii: Sporothrix causes delayed nodular lymphangitis following plant inoculation, rather than an acute red streak within 24–48 hours.
Exam pearl: Streptococcus pyogenes — Plant-thorn history alone does not prove sporotrichosis
Q54. An asymptomatic elective-surgery patient is found to carry MRSA in the nares. Which topical agent is commonly used for nasal decolonisation?
Recall paper: September 2020; Microbiology
A. Oral vancomycin
B. Intravenous metronidazole
C. Intranasal mupirocin
D. Oral fluconazole
Answer and explanation
C. Intranasal mupirocin
Mupirocin ointment applied intranasally is a common component of targeted MRSA decolonisation. Chlorhexidine washes are often added for skin decolonisation in accordance with local protocols.
A. Oral vancomycin: Oral vancomycin acts principally within the intestine because systemic absorption is poor; it does not treat bloodstream infection.
B. Intravenous metronidazole: Intravenous metronidazole is not equivalent to preferred oral luminal therapy for nonfulminant C. difficile disease.
D. Oral fluconazole: Fluconazole treats susceptible fungal infection; it is not an anti-MRSA decolonising drug or a luminal C. difficile agent.
Exam pearl: Intranasal mupirocin — Decolonisation is not the same as treating MRSA bacteraemia.
Q55. A patient with recurrent UTIs develops a branching staghorn renal calculus. Which bacterium is classically associated?
Recall paper: September 2020; Microbiology
A. Proteus mirabilis
B. Escherichia coli
C. Staphylococcus epidermidis
D. Streptococcus pyogenes
Answer and explanation
A. Proteus mirabilis
Proteus mirabilis expresses urease, which splits urea into ammonia, increases urinary pH and promotes magnesium ammonium phosphate (struvite) and carbonate apatite crystallisation. Recurrent urease-producing urinary infection is associated with large branching calculi.
B. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
C. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
Exam pearl: Proteus mirabilis — Commonest UTI organism is E. coli
Q56. An immunocompromised patient develops multiple violaceous vascular plaques characteristic of Kaposi sarcoma. Which virus is linked?
Recall paper: September 2020; Microbiology
A. Human papillomavirus 16
B. Human herpesvirus 8
C. Epstein–Barr virus
D. Cytomegalovirus
Answer and explanation
B. Human herpesvirus 8
Human herpesvirus 8, also called Kaposi sarcoma-associated herpesvirus, is the viral driver of Kaposi sarcoma. Lesions reflect proliferating spindle cells and abnormal angiogenesis.
A. Human papillomavirus 16: HPV16 is oncogenic in oropharyngeal and anogenital squamous epithelium, not the causal virus of Kaposi sarcoma.
C. Epstein–Barr virus: Epstein–Barr virus causes infectious mononucleosis and is linked to several lymphomas and nasopharyngeal carcinoma.
D. Cytomegalovirus: Cytomegalovirus is an important viral opportunistic infection after transplantation, particularly with immune suppression.
Exam pearl: Human herpesvirus 8 — Kaposi sarcoma = HHV-8, not HPV.
Q57. An immunocompromised patient develops multiple violaceous vascular plaques characteristic of Kaposi sarcoma. Which virus is linked?
Recall paper: September 2020; Microbiology
A. Human herpesvirus 8
B. Human papillomavirus 16
C. Epstein–Barr virus
D. Cytomegalovirus
Answer and explanation
A. Human herpesvirus 8
Human herpesvirus 8, also called Kaposi sarcoma-associated herpesvirus, is the viral driver of Kaposi sarcoma. Lesions reflect proliferating spindle cells and abnormal angiogenesis.
B. Human papillomavirus 16: HPV16 is oncogenic in oropharyngeal and anogenital squamous epithelium, not the causal virus of Kaposi sarcoma.
C. Epstein–Barr virus: Epstein–Barr virus causes infectious mononucleosis and is linked to several lymphomas and nasopharyngeal carcinoma.
D. Cytomegalovirus: Cytomegalovirus is an important viral opportunistic infection after transplantation, particularly with immune suppression.
Exam pearl: Human herpesvirus 8 — Kaposi sarcoma = HHV-8, not HPV.
Q58. A patient with recurrent UTIs develops a branching staghorn renal calculus. Which bacterium is classically associated?
Recall paper: September 2020; Microbiology
A. Escherichia coli
B. Staphylococcus epidermidis
C. Streptococcus pyogenes
D. Proteus mirabilis
Answer and explanation
D. Proteus mirabilis
Proteus mirabilis expresses urease, which splits urea into ammonia, increases urinary pH and promotes magnesium ammonium phosphate (struvite) and carbonate apatite crystallisation. Recurrent urease-producing urinary infection is associated with large branching calculi.
A. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
B. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
C. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
Exam pearl: Proteus mirabilis — Commonest UTI organism is E. coli
Q59. Which organ converts circulating lactate to glucose as part of the Cori cycle?
Recall paper: September 2020; Physiology
A. Lung
B. Bone
C. Spleen
D. Liver
Answer and explanation
D. Liver
In the Cori cycle, lactate generated by anaerobic glycolysis in skeletal muscle and erythrocytes is converted into glucose by hepatic gluconeogenesis. Glucose can then re-enter peripheral circulation.
A. Lung: The lungs perform gas exchange, not the dominant hepatic conversion of lactate back to glucose.
B. Bone: Bone serves structural and mineral-homeostasis functions, not the principal Cori-cycle glucose-regeneration pathway.
C. Spleen: The spleen filters blood and mounts immune responses; it is not a major gluconeogenic organ.
Exam pearl: Liver — Cori cycle: lactate to liver, glucose back to peripheral tissues.
Q60. An immunocompromised patient develops multiple violaceous vascular plaques characteristic of Kaposi sarcoma. Which virus is linked?
Recall paper: September 2020; Microbiology
A. Human herpesvirus 8
B. Human papillomavirus 16
C. Epstein–Barr virus
D. Cytomegalovirus
Answer and explanation
A. Human herpesvirus 8
Human herpesvirus 8, also called Kaposi sarcoma-associated herpesvirus, is the viral driver of Kaposi sarcoma. Lesions reflect proliferating spindle cells and abnormal angiogenesis.
B. Human papillomavirus 16: HPV16 is oncogenic in oropharyngeal and anogenital squamous epithelium, not the causal virus of Kaposi sarcoma.
C. Epstein–Barr virus: Epstein–Barr virus causes infectious mononucleosis and is linked to several lymphomas and nasopharyngeal carcinoma.
D. Cytomegalovirus: Cytomegalovirus is an important viral opportunistic infection after transplantation, particularly with immune suppression.
Exam pearl: Human herpesvirus 8 — Kaposi sarcoma = HHV-8, not HPV.
Q61. Which organ converts circulating lactate to glucose as part of the Cori cycle?
Recall paper: September 2020; Physiology
A. Liver
B. Lung
C. Bone
D. Spleen
Answer and explanation
A. Liver
In the Cori cycle, lactate generated by anaerobic glycolysis in skeletal muscle and erythrocytes is converted into glucose by hepatic gluconeogenesis. Glucose can then re-enter peripheral circulation.
B. Lung: The lungs perform gas exchange, not the dominant hepatic conversion of lactate back to glucose.
C. Bone: Bone serves structural and mineral-homeostasis functions, not the principal Cori-cycle glucose-regeneration pathway.
D. Spleen: The spleen filters blood and mounts immune responses; it is not a major gluconeogenic organ.
Exam pearl: Liver — Cori cycle: lactate to liver, glucose back to peripheral tissues.
Q62. Renal colic due to a ureteric calculus typically refers pain through which spinal segments?
Recall paper: September 2020; Anatomy
A. T11–L2
B. C2–C4
C. T2–T4
D. S3–S5 exclusively
Answer and explanation
A. T11–L2
Visceral afferents from the ureter enter around T11–L2, resulting in flank-to-groin referred pain along overlapping somatic dermatomes. Distribution shifts with stone location.
B. C2–C4: C2–C4 supplies or refers to a different anatomical region from the tissue or pathway described in the question.
C. T2–T4: T2–T4 supplies or refers to a different anatomical region from the tissue or pathway described in the question.
D. S3–S5 exclusively: S3–S5 exclusively supplies or refers to a different anatomical region from the tissue or pathway described in the question.
Exam pearl: T11–L2 — Ureteric colic classically radiates from loin to groin.
Q63. A contaminated traumatic wound rapidly develops malodour, gas and extensive muscle necrosis. What is the essential management principle?
Recall paper: January 2021; Microbiology
A. Topical antiseptic alone
B. Delay surgery until all cultures return
C. Oral doxycycline monotherapy
D. Urgent surgical debridement plus broad-spectrum antibiotics
Answer and explanation
D. Urgent surgical debridement plus broad-spectrum antibiotics
Clostridial myonecrosis and necrotising wound infection are surgical emergencies requiring immediate exploration and radical debridement. Empirical antimicrobials must cover Gram-positive, Gram-negative and anaerobic organisms, then be refined by cultures; targeted clostridial therapy usually includes penicillin plus clindamycin.
A. Topical antiseptic alone: Surface antisepsis cannot provide definitive therapy for deep established infection or replace necessary systemic therapy and source control.
B. Delay surgery until all cultures return: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
C. Oral doxycycline monotherapy: Doxycycline alone may lack the anaerobic or Gram-negative breadth necessary for necrotising or mixed traumatic infection.
Exam pearl: Urgent surgical debridement plus broad-spectrum antibiotics — No antibiotic substitutes for prompt surgical source control.
Q64. A psoas-region abscess compresses a nerve supplying skin over the lateral thigh, producing burning paraesthesia. Which nerve is involved?
Recall paper: January 2021; Anatomy
A. Femoral nerve motor branches
B. Obturator nerve
C. Lateral femoral cutaneous nerve
D. Common fibular nerve
Answer and explanation
C. Lateral femoral cutaneous nerve
The lateral femoral cutaneous nerve arises from L2–L3 and runs close to the iliacus and anterior superior iliac spine before passing beneath or through the inguinal ligament. Compression causes meralgia paraesthetica without motor weakness.
A. Femoral nerve motor branches: Femoral nerve motor branches supplies or refers to a different anatomical region from the tissue or pathway described in the question.
B. Obturator nerve: Obturator nerve supplies or refers to a different anatomical region from the tissue or pathway described in the question.
D. Common fibular nerve: Common fibular nerve supplies or refers to a different anatomical region from the tissue or pathway described in the question.
Exam pearl: Lateral femoral cutaneous nerve — Pure lateral-thigh sensory loss without weakness suggests lateral femoral cutaneous neuropathy.
Q65. Which organism is most commonly associated with haematogenous native pyogenic vertebral osteomyelitis in adults?
Recall paper: January 2021; Microbiology
A. Staphylococcus aureus
B. Clostridioides difficile
C. Staphylococcus epidermidis
D. Campylobacter jejuni
Answer and explanation
A. Staphylococcus aureus
Staphylococcus aureus is the leading cause of adult native vertebral osteomyelitis or pyogenic discitis. Blood cultures, inflammatory markers and MRI help establish the diagnosis and define the extent of infection.
B. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
C. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
Exam pearl: Staphylococcus aureus — Native pyogenic discitis = S. aureus until proved otherwise
Q66. An individual with chronic limb lymphoedema develops a hot, poorly demarcated, nonpurulent cellulitis. What organism is classically responsible?
Recall paper: January 2021; Microbiology
A. Pseudomonas aeruginosa
B. Candida albicans
C. Streptococcus pyogenes
D. Clostridioides difficile
Answer and explanation
C. Streptococcus pyogenes
Beta-haemolytic streptococci commonly cause spreading nonpurulent cellulitis, and lymphoedema markedly increases recurrence risk. Management includes treatment of infection and attention to skin integrity and underlying oedema.
A. Pseudomonas aeruginosa: Pseudomonas aeruginosa is prominent in burns, catheter-related infection and healthcare-associated pneumonia, not the hallmark being asked.
B. Candida albicans: Candida albicans is a yeast causing thrush and opportunistic mucosal or invasive candidiasis, rather than this syndrome.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Streptococcus pyogenes — Streptococci predominate in typical nonpurulent cellulitis
Q67. A patient with advanced untreated HIV develops disseminated infection with generalised lymphadenopathy and constitutional symptoms. Which mycobacterium is important?
Recall paper: January 2021; Microbiology
A. Mycobacterium leprae
B. Enterobius vermicularis
C. Mycobacterium avium complex
D. Staphylococcus saprophyticus
Answer and explanation
C. Mycobacterium avium complex
Disseminated Mycobacterium avium complex infection occurs particularly at very low CD4 counts and can cause fever, weight loss, anaemia and lymphadenopathy. Blood and tissue cultures can confirm infection.
A. Mycobacterium leprae: M. leprae causes chronic peripheral neuropathy and skin lesions, not the acute illness specified.
B. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
D. Staphylococcus saprophyticus: S. saprophyticus can cause uncomplicated UTI, particularly in young women, but is not the principal overall cause or classic infection-stone pathogen.
Exam pearl: Mycobacterium avium complex — CD4 count and disseminated symptoms are necessary contextual clues.
Q68. How should a flexible endoscope that contacts intact gastrointestinal mucosa be reprocessed at minimum?
Recall paper: January 2021; Microbiology
A. Thorough cleaning followed by high-level disinfection
B. Brief alcohol wiping alone
C. Low-level disinfection
D. Routine dry-heat sterilisation regardless of instrument compatibility
Answer and explanation
A. Thorough cleaning followed by high-level disinfection
Flexible GI endoscopes are Spaulding semicritical devices because they contact mucosa without normally entering sterile tissue. They require meticulous channel cleaning and at least high-level disinfection according to validated manufacturer instructions.
B. Brief alcohol wiping alone: Cleaning or low-level surface treatment alone is not a validated substitute for the required level of medical-device reprocessing.
C. Low-level disinfection: Low-level disinfection is reserved for noncritical equipment contacting intact skin, not semicritical or critical devices.
D. Routine dry-heat sterilisation regardless of instrument compatibility: The proposed reprocessing choice ignores the equipment classification or heat sensitivity; use an appropriate validated method.
Exam pearl: Thorough cleaning followed by high-level disinfection — A specific chemical named in a historical recall is not universally the “best” method
Q69. A psoas-region abscess compresses a nerve supplying skin over the lateral thigh, producing burning paraesthesia. Which nerve is involved?
Recall paper: January 2021; Anatomy
A. Femoral nerve motor branches
B. Obturator nerve
C. Common fibular nerve
D. Lateral femoral cutaneous nerve
Answer and explanation
D. Lateral femoral cutaneous nerve
The lateral femoral cutaneous nerve arises from L2–L3 and runs close to the iliacus and anterior superior iliac spine before passing beneath or through the inguinal ligament. Compression causes meralgia paraesthetica without motor weakness.
A. Femoral nerve motor branches: Femoral nerve motor branches supplies or refers to a different anatomical region from the tissue or pathway described in the question.
B. Obturator nerve: Obturator nerve supplies or refers to a different anatomical region from the tissue or pathway described in the question.
C. Common fibular nerve: Common fibular nerve supplies or refers to a different anatomical region from the tissue or pathway described in the question.
Exam pearl: Lateral femoral cutaneous nerve — Pure lateral-thigh sensory loss without weakness suggests lateral femoral cutaneous neuropathy.
Q70. How should a flexible endoscope that contacts intact gastrointestinal mucosa be reprocessed at minimum?
Recall paper: January 2021; Microbiology
A. Brief alcohol wiping alone
B. Low-level disinfection
C. Routine dry-heat sterilisation regardless of instrument compatibility
D. Thorough cleaning followed by high-level disinfection
Answer and explanation
D. Thorough cleaning followed by high-level disinfection
Flexible GI endoscopes are Spaulding semicritical devices because they contact mucosa without normally entering sterile tissue. They require meticulous channel cleaning and at least high-level disinfection according to validated manufacturer instructions.
A. Brief alcohol wiping alone: Cleaning or low-level surface treatment alone is not a validated substitute for the required level of medical-device reprocessing.
B. Low-level disinfection: Low-level disinfection is reserved for noncritical equipment contacting intact skin, not semicritical or critical devices.
C. Routine dry-heat sterilisation regardless of instrument compatibility: The proposed reprocessing choice ignores the equipment classification or heat sensitivity; use an appropriate validated method.
Exam pearl: Thorough cleaning followed by high-level disinfection — A specific chemical named in a historical recall is not universally the “best” method
Q71. Which organism is most commonly associated with haematogenous native pyogenic vertebral osteomyelitis in adults?
Recall paper: January 2021; Microbiology
A. Clostridioides difficile
B. Staphylococcus epidermidis
C. Campylobacter jejuni
D. Staphylococcus aureus
Answer and explanation
D. Staphylococcus aureus
Staphylococcus aureus is the leading cause of adult native vertebral osteomyelitis or pyogenic discitis. Blood cultures, inflammatory markers and MRI help establish the diagnosis and define the extent of infection.
A. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
B. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
C. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
Exam pearl: Staphylococcus aureus — Native pyogenic discitis = S. aureus until proved otherwise
Q72. A contaminated traumatic wound rapidly develops malodour, gas and extensive muscle necrosis. What is the essential management principle?
Recall paper: January 2021; Microbiology
A. Topical antiseptic alone
B. Delay surgery until all cultures return
C. Urgent surgical debridement plus broad-spectrum antibiotics
D. Oral doxycycline monotherapy
Answer and explanation
C. Urgent surgical debridement plus broad-spectrum antibiotics
Clostridial myonecrosis and necrotising wound infection are surgical emergencies requiring immediate exploration and radical debridement. Empirical antimicrobials must cover Gram-positive, Gram-negative and anaerobic organisms, then be refined by cultures; targeted clostridial therapy usually includes penicillin plus clindamycin.
A. Topical antiseptic alone: Surface antisepsis cannot provide definitive therapy for deep established infection or replace necessary systemic therapy and source control.
B. Delay surgery until all cultures return: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
D. Oral doxycycline monotherapy: Doxycycline alone may lack the anaerobic or Gram-negative breadth necessary for necrotising or mixed traumatic infection.
Exam pearl: Urgent surgical debridement plus broad-spectrum antibiotics — No antibiotic substitutes for prompt surgical source control.
Q73. A patient with advanced untreated HIV develops disseminated infection with generalised lymphadenopathy and constitutional symptoms. Which mycobacterium is important?
Recall paper: January 2021; Microbiology
A. Mycobacterium avium complex
B. Mycobacterium leprae
C. Enterobius vermicularis
D. Staphylococcus saprophyticus
Answer and explanation
A. Mycobacterium avium complex
Disseminated Mycobacterium avium complex infection occurs particularly at very low CD4 counts and can cause fever, weight loss, anaemia and lymphadenopathy. Blood and tissue cultures can confirm infection.
B. Mycobacterium leprae: M. leprae causes chronic peripheral neuropathy and skin lesions, not the acute illness specified.
C. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
D. Staphylococcus saprophyticus: S. saprophyticus can cause uncomplicated UTI, particularly in young women, but is not the principal overall cause or classic infection-stone pathogen.
Exam pearl: Mycobacterium avium complex — CD4 count and disseminated symptoms are necessary contextual clues.
Q74. A patient with advanced dental disease develops a deep odontogenic abscess. Which bacterial component is characteristic?
Recall paper: Mixed Jan/Sep 2021; Microbiology
A. Anaerobic oral flora including Bacteroides/Prevotella species
B. Salmonella Typhi
C. Neisseria meningitidis
D. Bordetella pertussis
Answer and explanation
A. Anaerobic oral flora including Bacteroides/Prevotella species
Odontogenic infection is generally polymicrobial, with viridans streptococci and anaerobes such as Prevotella, Fusobacterium and related Bacteroides groups. Drainage and removal of the dental source are central.
B. Salmonella Typhi: Salmonella Typhi causes enteric fever, generally a systemic febrile illness rather than the condition in this stem.
C. Neisseria meningitidis: Neisseria meningitidis is a Gram-negative diplococcus causing meningococcal meningitis and sepsis.
D. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
Exam pearl: Anaerobic oral flora including Bacteroides/Prevotella species — Dental abscesses are mixed flora
Q75. A diabetic patient develops a painful boil centred on a neck hair follicle. What is the most likely bacterium?
Recall paper: Mixed Jan/Sep 2021; Microbiology
A. Candida albicans
B. Streptococcus pneumoniae
C. Enterococcus faecalis
D. Staphylococcus aureus
Answer and explanation
D. Staphylococcus aureus
S. aureus is the classic cause of furuncles and carbuncles due to infection of hair follicles and surrounding tissue. A fluctuant abscess is primarily treated by drainage where appropriate.
A. Candida albicans: Candida albicans is a yeast causing thrush and opportunistic mucosal or invasive candidiasis, rather than this syndrome.
B. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
C. Enterococcus faecalis: Enterococcus faecalis may cause urinary or endovascular infection but is not the most characteristic answer here.
Exam pearl: Staphylococcus aureus — Furuncle or carbuncle = S. aureus.
Q76. A solid-organ transplant recipient in the intermediate post-transplant period develops unexplained pneumonitis and systemic symptoms. What opportunistic virus should be investigated?
Recall paper: Mixed Jan/Sep 2021; Microbiology
A. Epstein–Barr virus
B. Human papillomavirus
C. Cytomegalovirus
D. Hepatitis A virus
Answer and explanation
C. Cytomegalovirus
CMV can produce a viral syndrome and tissue-invasive disease including pneumonitis after transplantation. Risk is affected by donor/recipient serostatus, prophylaxis, immunosuppression and time since transplant.
A. Epstein–Barr virus: Epstein–Barr virus causes infectious mononucleosis and is linked to several lymphomas and nasopharyngeal carcinoma.
B. Human papillomavirus: Human papillomavirus causes epithelial papillomas and is associated with selected anogenital and oropharyngeal carcinomas.
D. Hepatitis A virus: Hepatitis A virus causes faecal–oral acute hepatitis rather than this bacterial or parasitic disease.
Exam pearl: Cytomegalovirus — A transplant patient’s pneumonia cannot be diagnosed as CMV from transplant status alone
Q77. A puncture injury to the fingertip is followed by a tender, tense, fluctuant pulp-space infection. Which pathogen is most likely?
Recall paper: April 2021; Microbiology
A. Streptococcus pneumoniae
B. Escherichia coli
C. Staphylococcus aureus
D. Clostridioides difficile
Answer and explanation
C. Staphylococcus aureus
S. aureus commonly causes a felon, an abscess within the fibrous septa of the digital pulp. Closed compartment pressure can threaten perfusion and necessitate timely drainage.
A. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
B. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Felon = closed-space pulp infection, most often Staphylococcus aureus.
Q78. Which oncogenic viral type is strongly associated with oropharyngeal squamous cell carcinoma?
Recall paper: April 2021; Microbiology
A. Epstein–Barr virus
B. Human herpesvirus 8
C. Human papillomavirus type 16
D. Hepatitis A virus
Answer and explanation
C. Human papillomavirus type 16
High-risk HPV, particularly HPV16, is linked to a distinct subset of oropharyngeal squamous cell carcinomas. p16 immunohistochemistry is a commonly used surrogate marker in suitable pathological settings.
A. Epstein–Barr virus: Epstein–Barr virus causes infectious mononucleosis and is linked to several lymphomas and nasopharyngeal carcinoma.
B. Human herpesvirus 8: Human herpesvirus 8 is the Kaposi sarcoma-associated herpesvirus rather than this condition.
D. Hepatitis A virus: Hepatitis A virus causes faecal–oral acute hepatitis rather than this bacterial or parasitic disease.
Exam pearl: Human papillomavirus type 16 — Oropharynx = HPV16
Q79. Why do inflamed wound edges become swollen and oedematous during acute inflammation?
Recall paper: April 2021; Pathology
A. Reduced capillary blood flow with no leakage
B. Failure of all neutrophil migration
C. Complete occlusion of lymphatic channels in every case
D. Increased vascular permeability with exudation
Answer and explanation
D. Increased vascular permeability with exudation
Mediators such as histamine and inflammatory cytokines enhance microvascular permeability, allowing protein-rich exudate to move into interstitial tissue. Vasodilation contributes erythema and warmth.
A. Reduced capillary blood flow with no leakage: This omits necessary evaluation or infection control and does not address the clinical risk described.
B. Failure of all neutrophil migration: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
C. Complete occlusion of lymphatic channels in every case: Inflammatory swelling can arise from increased microvascular leakage without complete mechanical lymphatic obstruction.
Exam pearl: Increased vascular permeability with exudation — Permeability explains oedema
Q80. An ulcer with undermined violaceous borders develops around an ileostomy in a patient with ulcerative colitis. Which condition is most likely?
Recall paper: April 2021; Pathology
A. Erythema nodosum
B. Pyoderma gangrenosum
C. Squamous cell carcinoma
D. Impetigo
Answer and explanation
B. Pyoderma gangrenosum
Pyoderma gangrenosum is a neutrophilic dermatosis associated with inflammatory bowel disease. Painful rapidly expanding ulcers may arise around a stoma and worsen after trauma (pathergy).
A. Erythema nodosum: Erythema nodosum is a different morphological finding and is not the distinctive clinical feature requested.
C. Squamous cell carcinoma: This epithelial malignancy has a different ulcerative or mass-forming course from the inflammatory lesion described.
D. Impetigo: Impetigo is a superficial crusting epidermal bacterial infection rather than a deep neutrophilic dermatosis or ulcerative process.
Exam pearl: Pyoderma gangrenosum — Despite the name, pyoderma gangrenosum is not primarily a bacterial infection.
Q81. Which oncogenic viral type is strongly associated with oropharyngeal squamous cell carcinoma?
Recall paper: April 2021; Microbiology
A. Epstein–Barr virus
B. Human herpesvirus 8
C. Hepatitis A virus
D. Human papillomavirus type 16
Answer and explanation
D. Human papillomavirus type 16
High-risk HPV, particularly HPV16, is linked to a distinct subset of oropharyngeal squamous cell carcinomas. p16 immunohistochemistry is a commonly used surrogate marker in suitable pathological settings.
A. Epstein–Barr virus: Epstein–Barr virus causes infectious mononucleosis and is linked to several lymphomas and nasopharyngeal carcinoma.
B. Human herpesvirus 8: Human herpesvirus 8 is the Kaposi sarcoma-associated herpesvirus rather than this condition.
C. Hepatitis A virus: Hepatitis A virus causes faecal–oral acute hepatitis rather than this bacterial or parasitic disease.
Exam pearl: Human papillomavirus type 16 — Oropharynx = HPV16
Q82. An ulcer with undermined violaceous borders develops around an ileostomy in a patient with ulcerative colitis. Which condition is most likely?
Recall paper: April 2021; Pathology
A. Erythema nodosum
B. Pyoderma gangrenosum
C. Squamous cell carcinoma
D. Impetigo
Answer and explanation
B. Pyoderma gangrenosum
Pyoderma gangrenosum is a neutrophilic dermatosis associated with inflammatory bowel disease. Painful rapidly expanding ulcers may arise around a stoma and worsen after trauma (pathergy).
A. Erythema nodosum: Erythema nodosum is a different morphological finding and is not the distinctive clinical feature requested.
C. Squamous cell carcinoma: This epithelial malignancy has a different ulcerative or mass-forming course from the inflammatory lesion described.
D. Impetigo: Impetigo is a superficial crusting epidermal bacterial infection rather than a deep neutrophilic dermatosis or ulcerative process.
Exam pearl: Pyoderma gangrenosum — Despite the name, pyoderma gangrenosum is not primarily a bacterial infection.
Q83. A sheep farmer has a hepatic cyst containing daughter cysts. Which parasite causes this presentation?
Recall paper: April 2021; Microbiology
A. Echinococcus granulosus
B. Enterobius vermicularis
C. Entamoeba histolytica
D. Schistosoma haematobium
Answer and explanation
A. Echinococcus granulosus
The dog–sheep lifecycle of Echinococcus granulosus leads to cystic hydatid disease, usually involving liver and lung. Daughter cysts and hydatid sand are characteristic imaging or pathological features.
B. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
C. Entamoeba histolytica: Entamoeba histolytica causes amoebic colitis and sometimes liver abscess, not this specific condition.
D. Schistosoma haematobium: Schistosoma haematobium produces urinary schistosomiasis, haematuria and increased squamous bladder-cancer risk.
Exam pearl: Echinococcus granulosus — Hydatid liver cyst with daughter cysts = E. granulosus.
Q84. Which virus is particularly implicated in post-transplant lymphoproliferative disorder?
Recall paper: April 2021; Microbiology
A. Hepatitis A virus
B. Human papillomavirus
C. Epstein–Barr virus
D. Rotavirus
Answer and explanation
C. Epstein–Barr virus
EBV-associated B-cell proliferation under immunosuppression is central to many post-transplant lymphoproliferative disorders. Risk depends on immune suppression intensity, donor/recipient serostatus and transplant type.
A. Hepatitis A virus: Hepatitis A virus causes faecal–oral acute hepatitis rather than this bacterial or parasitic disease.
B. Human papillomavirus: Human papillomavirus causes epithelial papillomas and is associated with selected anogenital and oropharyngeal carcinomas.
D. Rotavirus: Rotavirus causes acute viral gastroenteritis, especially in children.
Exam pearl: Epstein–Barr virus — Post-transplant lymphadenopathy: consider EBV-associated PTLD.
Q85. An immunocompromised patient develops chronic weight loss, cough and haemoptysis, raising concern for tuberculosis. Which organism must be excluded?
Recall paper: April 2021; Microbiology
A. Staphylococcus epidermidis
B. Enterobius vermicularis
C. Mycobacterium tuberculosis
D. Bartonella henselae
Answer and explanation
C. Mycobacterium tuberculosis
Pulmonary tuberculosis is caused by M. tuberculosis and may produce chronic constitutional symptoms, cavitation and haemoptysis. In HIV-associated advanced immunosuppression, imaging may be atypical or disseminated rather than apical.
A. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
B. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
D. Bartonella henselae: Bartonella henselae classically causes regional cat-scratch lymphadenopathy, not this condition.
Exam pearl: Mycobacterium tuberculosis — Steroids plus weight loss and haemoptysis should trigger a TB evaluation.
Q86. Which organ converts circulating lactate to glucose as part of the Cori cycle?
Recall paper: September 2021; Physiology
A. Lung
B. Bone
C. Spleen
D. Liver
Answer and explanation
D. Liver
In the Cori cycle, lactate generated by anaerobic glycolysis in skeletal muscle and erythrocytes is converted into glucose by hepatic gluconeogenesis. Glucose can then re-enter peripheral circulation.
A. Lung: The lungs perform gas exchange, not the dominant hepatic conversion of lactate back to glucose.
B. Bone: Bone serves structural and mineral-homeostasis functions, not the principal Cori-cycle glucose-regeneration pathway.
C. Spleen: The spleen filters blood and mounts immune responses; it is not a major gluconeogenic organ.
Exam pearl: Liver — Cori cycle: lactate to liver, glucose back to peripheral tissues.
Q87. An immunocompromised patient develops multiple violaceous vascular plaques characteristic of Kaposi sarcoma. Which virus is linked?
Recall paper: September 2021; Microbiology
A. Human papillomavirus 16
B. Human herpesvirus 8
C. Epstein–Barr virus
D. Cytomegalovirus
Answer and explanation
B. Human herpesvirus 8
Human herpesvirus 8, also called Kaposi sarcoma-associated herpesvirus, is the viral driver of Kaposi sarcoma. Lesions reflect proliferating spindle cells and abnormal angiogenesis.
A. Human papillomavirus 16: HPV16 is oncogenic in oropharyngeal and anogenital squamous epithelium, not the causal virus of Kaposi sarcoma.
C. Epstein–Barr virus: Epstein–Barr virus causes infectious mononucleosis and is linked to several lymphomas and nasopharyngeal carcinoma.
D. Cytomegalovirus: Cytomegalovirus is an important viral opportunistic infection after transplantation, particularly with immune suppression.
Exam pearl: Human herpesvirus 8 — Kaposi sarcoma = HHV-8, not HPV.
Q88. A patient with advanced dental disease develops a deep odontogenic abscess. Which bacterial component is characteristic?
Recall paper: September 2021; Microbiology
A. Salmonella Typhi
B. Neisseria meningitidis
C. Anaerobic oral flora including Bacteroides/Prevotella species
D. Bordetella pertussis
Answer and explanation
C. Anaerobic oral flora including Bacteroides/Prevotella species
Odontogenic infection is generally polymicrobial, with viridans streptococci and anaerobes such as Prevotella, Fusobacterium and related Bacteroides groups. Drainage and removal of the dental source are central.
A. Salmonella Typhi: Salmonella Typhi causes enteric fever, generally a systemic febrile illness rather than the condition in this stem.
B. Neisseria meningitidis: Neisseria meningitidis is a Gram-negative diplococcus causing meningococcal meningitis and sepsis.
D. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
Exam pearl: Anaerobic oral flora including Bacteroides/Prevotella species — Dental abscesses are mixed flora
Q89. Which encapsulated bacterium is historically associated with severe childhood epiglottitis?
Recall paper: September 2021; Microbiology
A. Haemophilus influenzae type b
B. Bordetella pertussis
C. Clostridium perfringens
D. Staphylococcus epidermidis
Answer and explanation
A. Haemophilus influenzae type b
Hib historically caused childhood epiglottitis, classically with fever, drooling, dysphagia and stridor. Widespread Hib vaccination has markedly reduced its incidence, and other organisms cause modern cases.
B. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
C. Clostridium perfringens: Clostridium perfringens is associated with clostridial myonecrosis, not this organism-specific diagnosis.
D. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
Exam pearl: Haemophilus influenzae type b — Epiglottitis = airway emergency
Q90. A patient with recurrent UTIs develops a branching staghorn renal calculus. Which bacterium is classically associated?
Recall paper: September 2021; Microbiology
A. Escherichia coli
B. Proteus mirabilis
C. Staphylococcus epidermidis
D. Streptococcus pyogenes
Answer and explanation
B. Proteus mirabilis
Proteus mirabilis expresses urease, which splits urea into ammonia, increases urinary pH and promotes magnesium ammonium phosphate (struvite) and carbonate apatite crystallisation. Recurrent urease-producing urinary infection is associated with large branching calculi.
A. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
C. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
Exam pearl: Proteus mirabilis — Commonest UTI organism is E. coli
Q91. A diabetic patient develops a painful boil centred on a neck hair follicle. What is the most likely bacterium?
Recall paper: September 2021; Microbiology
A. Candida albicans
B. Streptococcus pneumoniae
C. Staphylococcus aureus
D. Enterococcus faecalis
Answer and explanation
C. Staphylococcus aureus
S. aureus is the classic cause of furuncles and carbuncles due to infection of hair follicles and surrounding tissue. A fluctuant abscess is primarily treated by drainage where appropriate.
A. Candida albicans: Candida albicans is a yeast causing thrush and opportunistic mucosal or invasive candidiasis, rather than this syndrome.
B. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
D. Enterococcus faecalis: Enterococcus faecalis may cause urinary or endovascular infection but is not the most characteristic answer here.
Exam pearl: Staphylococcus aureus — Furuncle or carbuncle = S. aureus.
Q92. Tender ascending red streaks develop from a recent skin puncture. What is the classic pathogen?
Recall paper: September 2021; Microbiology
A. Staphylococcus epidermidis
B. Escherichia coli
C. Sporothrix schenckii
D. Streptococcus pyogenes
Answer and explanation
D. Streptococcus pyogenes
Group A beta-haemolytic streptococci commonly cause rapidly advancing nonpurulent cellulitis and lymphangitis. The tender proximal erythematous streaks reflect inflammation of superficial lymphatic vessels.
A. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
B. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
C. Sporothrix schenckii: Sporothrix causes delayed nodular lymphangitis following plant inoculation, rather than an acute red streak within 24–48 hours.
Exam pearl: Streptococcus pyogenes — Plant-thorn history alone does not prove sporotrichosis
Q93. A patient with advanced dental disease develops a deep odontogenic abscess. Which bacterial component is characteristic?
Recall paper: May 2022; Microbiology
A. Salmonella Typhi
B. Neisseria meningitidis
C. Anaerobic oral flora including Bacteroides/Prevotella species
D. Bordetella pertussis
Answer and explanation
C. Anaerobic oral flora including Bacteroides/Prevotella species
Odontogenic infection is generally polymicrobial, with viridans streptococci and anaerobes such as Prevotella, Fusobacterium and related Bacteroides groups. Drainage and removal of the dental source are central.
A. Salmonella Typhi: Salmonella Typhi causes enteric fever, generally a systemic febrile illness rather than the condition in this stem.
B. Neisseria meningitidis: Neisseria meningitidis is a Gram-negative diplococcus causing meningococcal meningitis and sepsis.
D. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
Exam pearl: Anaerobic oral flora including Bacteroides/Prevotella species — Dental abscesses are mixed flora
Q94. Tender ascending red streaks develop from a recent skin puncture. What is the classic pathogen?
Recall paper: May 2022; Microbiology
A. Staphylococcus epidermidis
B. Escherichia coli
C. Streptococcus pyogenes
D. Sporothrix schenckii
Answer and explanation
C. Streptococcus pyogenes
Group A beta-haemolytic streptococci commonly cause rapidly advancing nonpurulent cellulitis and lymphangitis. The tender proximal erythematous streaks reflect inflammation of superficial lymphatic vessels.
A. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
B. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
D. Sporothrix schenckii: Sporothrix causes delayed nodular lymphangitis following plant inoculation, rather than an acute red streak within 24–48 hours.
Exam pearl: Streptococcus pyogenes — Plant-thorn history alone does not prove sporotrichosis
Q95. A sexually active young man has fever, dysuria, urethral discharge and gradual unilateral epididymal pain. Which organism is a common cause?
Recall paper: May 2022; Microbiology
A. Escherichia coli
B. Staphylococcus epidermidis
C. Mumps virus
D. Chlamydia trachomatis
Answer and explanation
D. Chlamydia trachomatis
C. trachomatis is a frequent cause of epididymitis in younger sexually active men, often with associated urethritis. Gonorrhoea is another important STI cause; testing and empirical treatment should address relevant pathogens.
A. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
B. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
C. Mumps virus: Mumps can cause viral orchitis, usually associated with parotitis, rather than typical sexually transmitted urethritis with discharge.
Exam pearl: Chlamydia trachomatis — Never allow a presumed diagnosis of epididymitis to delay evaluation of possible testicular torsion.
Q96. An asymptomatic elective-surgery patient is found to carry MRSA in the nares. Which topical agent is commonly used for nasal decolonisation?
Recall paper: May 2022; Microbiology
A. Oral vancomycin
B. Intranasal mupirocin
C. Intravenous metronidazole
D. Oral fluconazole
Answer and explanation
B. Intranasal mupirocin
Mupirocin ointment applied intranasally is a common component of targeted MRSA decolonisation. Chlorhexidine washes are often added for skin decolonisation in accordance with local protocols.
A. Oral vancomycin: Oral vancomycin acts principally within the intestine because systemic absorption is poor; it does not treat bloodstream infection.
C. Intravenous metronidazole: Intravenous metronidazole is not equivalent to preferred oral luminal therapy for nonfulminant C. difficile disease.
D. Oral fluconazole: Fluconazole treats susceptible fungal infection; it is not an anti-MRSA decolonising drug or a luminal C. difficile agent.
Exam pearl: Intranasal mupirocin — Decolonisation is not the same as treating MRSA bacteraemia.
Q97. A patient taking chronic prednisolone is booked for major surgery. What aspect of perioperative care must be evaluated?
Recall paper: May 2022; Pharmacology
A. Risk of hypothalamic–pituitary–adrenal suppression
B. Routine discontinuation of all steroid therapy
C. Automatic tenfold dose increase for every operation
D. Steroids have no perioperative implications
Answer and explanation
A. Risk of hypothalamic–pituitary–adrenal suppression
Long-term systemic glucocorticoids may suppress endogenous cortisol responses and require assessment of steroid dose, duration, surgical stress and adrenal insufficiency risk. Supplemental perioperative hydrocortisone is individualised rather than automatically prescribed at a fixed high dose.
B. Routine discontinuation of all steroid therapy: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
C. Automatic tenfold dose increase for every operation: Stress-dose steroid decisions depend on chronic dose, adrenal suppression and operative stress; no universal tenfold rule applies.
D. Steroids have no perioperative implications: This omits necessary evaluation or infection control and does not address the clinical risk described.
Exam pearl: Risk of hypothalamic–pituitary–adrenal suppression — “Give stress-dose steroids to everyone” is an oversimplified historical rule.
Q98. For a reusable arthroscope entering a normally sterile joint, which reprocessing endpoint should be aimed for?
Recall paper: May 2022; Microbiology
A. Simple alcohol wipe
B. Sterilisation using a validated compatible process
C. Low-level disinfection
D. Soap-and-water rinse alone
Answer and explanation
B. Sterilisation using a validated compatible process
Arthroscopes enter sterile tissue and are classified as critical instruments; sterilisation is recommended using the device-compatible validated process, often steam for heat-stable devices. High-level disinfection is not synonymous with sterilisation.
A. Simple alcohol wipe: Cleaning or low-level surface treatment alone is not a validated substitute for the required level of medical-device reprocessing.
C. Low-level disinfection: Low-level disinfection is reserved for noncritical equipment contacting intact skin, not semicritical or critical devices.
D. Soap-and-water rinse alone: Cleaning or low-level surface treatment alone is not a validated substitute for the required level of medical-device reprocessing.
Exam pearl: Sterilisation using a validated compatible process — An older recall naming glutaraldehyde as best sterilisation fails to distinguish disinfection from sterilisation.
Q99. A solid-organ transplant recipient in the intermediate post-transplant period develops unexplained pneumonitis and systemic symptoms. What opportunistic virus should be investigated?
Recall paper: May 2022; Microbiology
A. Epstein–Barr virus
B. Cytomegalovirus
C. Human papillomavirus
D. Hepatitis A virus
Answer and explanation
B. Cytomegalovirus
CMV can produce a viral syndrome and tissue-invasive disease including pneumonitis after transplantation. Risk is affected by donor/recipient serostatus, prophylaxis, immunosuppression and time since transplant.
A. Epstein–Barr virus: Epstein–Barr virus causes infectious mononucleosis and is linked to several lymphomas and nasopharyngeal carcinoma.
C. Human papillomavirus: Human papillomavirus causes epithelial papillomas and is associated with selected anogenital and oropharyngeal carcinomas.
D. Hepatitis A virus: Hepatitis A virus causes faecal–oral acute hepatitis rather than this bacterial or parasitic disease.
Exam pearl: Cytomegalovirus — A transplant patient’s pneumonia cannot be diagnosed as CMV from transplant status alone
Q100. A child develops microangiopathic haemolysis, thrombocytopenia and acute kidney injury following diarrhoeal illness. Which pathogen is classically implicated?
Recall paper: May 2022; Microbiology
A. Streptococcus pyogenes
B. Clostridioides difficile
C. Shiga toxin-producing Escherichia coli
D. Bacteroides fragilis
Answer and explanation
C. Shiga toxin-producing Escherichia coli
Shiga toxin-producing E. coli, classically O157:H7 or other toxin-producing strains, causes typical diarrhoea-associated haemolytic uraemic syndrome by endothelial injury. The key triad is haemolytic anaemia, thrombocytopenia and acute kidney injury.
A. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
B. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
D. Bacteroides fragilis: B. fragilis is a colonic anaerobe associated with intra-abdominal abscess, not the characteristic organism in this vignette.
Exam pearl: Shiga toxin-producing Escherichia coli — Haematuria after a sore throat alone is not sufficient to diagnose HUS
Q101. A recent traveller develops crampy bloody diarrhoea; investigation supports invasive amoebic colitis. What organism is responsible?
Recall paper: May 2022; Microbiology
A. Campylobacter jejuni
B. Entamoeba histolytica
C. Enterobius vermicularis
D. Hepatitis A virus
Answer and explanation
B. Entamoeba histolytica
Entamoeba histolytica invades colonic mucosa and can cause bloody diarrhoea, flask-shaped ulcers and extraintestinal liver abscess. Specific stool antigen or molecular testing is more discriminatory than cyst microscopy alone.
A. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
C. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
D. Hepatitis A virus: Hepatitis A virus causes faecal–oral acute hepatitis rather than this bacterial or parasitic disease.
Exam pearl: Entamoeba histolytica — Bloody diarrhoea after travel alone is not diagnostic of amoebiasis
Q102. A child has nocturnal pruritus ani and a positive perianal adhesive-tape test. What is an appropriate antiparasitic treatment?
Recall paper: May 2022; Microbiology
A. Metronidazole
B. Vancomycin
C. Mebendazole
D. Tinidazole
Answer and explanation
C. Mebendazole
Mebendazole treats Enterobius vermicularis (pinworm), whose eggs are laid around the anus at night. A repeat dose after about two weeks and simultaneous household hygiene measures help prevent reinfection.
A. Metronidazole: Metronidazole is active against many anaerobic bacteria and protozoa, but the exact indication or route differs in this stem.
B. Vancomycin: Vancomycin is a glycopeptide used systemically against serious susceptible Gram-positive infections and orally for C. difficile.
D. Tinidazole: Tinidazole is a nitroimidazole used against certain anaerobic and protozoal infections, but not the preferred answer to this precise question.
Exam pearl: Mebendazole — The tape test and nocturnal pruritus point to pinworm, not amoebic dysentery.
Q103. Which organism is most commonly associated with haematogenous native pyogenic vertebral osteomyelitis in adults?
Recall paper: May 2022; Microbiology
A. Staphylococcus aureus
B. Clostridioides difficile
C. Staphylococcus epidermidis
D. Campylobacter jejuni
Answer and explanation
A. Staphylococcus aureus
Staphylococcus aureus is the leading cause of adult native vertebral osteomyelitis or pyogenic discitis. Blood cultures, inflammatory markers and MRI help establish the diagnosis and define the extent of infection.
B. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
C. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
Exam pearl: Staphylococcus aureus — Native pyogenic discitis = S. aureus until proved otherwise
Q104. A sexually active young man has fever, dysuria, urethral discharge and gradual unilateral epididymal pain. Which organism is a common cause?
Recall paper: May 2022; Microbiology
A. Escherichia coli
B. Staphylococcus epidermidis
C. Chlamydia trachomatis
D. Mumps virus
Answer and explanation
C. Chlamydia trachomatis
C. trachomatis is a frequent cause of epididymitis in younger sexually active men, often with associated urethritis. Gonorrhoea is another important STI cause; testing and empirical treatment should address relevant pathogens.
A. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
B. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Mumps virus: Mumps can cause viral orchitis, usually associated with parotitis, rather than typical sexually transmitted urethritis with discharge.
Exam pearl: Chlamydia trachomatis — Never allow a presumed diagnosis of epididymitis to delay evaluation of possible testicular torsion.
Q105. Tender ascending red streaks develop from a recent skin puncture. What is the classic pathogen?
Recall paper: May 2022; Microbiology
A. Staphylococcus epidermidis
B. Streptococcus pyogenes
C. Escherichia coli
D. Sporothrix schenckii
Answer and explanation
B. Streptococcus pyogenes
Group A beta-haemolytic streptococci commonly cause rapidly advancing nonpurulent cellulitis and lymphangitis. The tender proximal erythematous streaks reflect inflammation of superficial lymphatic vessels.
A. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
C. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
D. Sporothrix schenckii: Sporothrix causes delayed nodular lymphangitis following plant inoculation, rather than an acute red streak within 24–48 hours.
Exam pearl: Streptococcus pyogenes — Plant-thorn history alone does not prove sporotrichosis
Q106. An asymptomatic elective-surgery patient is found to carry MRSA in the nares. Which topical agent is commonly used for nasal decolonisation?
Recall paper: May 2022; Microbiology
A. Oral vancomycin
B. Intravenous metronidazole
C. Intranasal mupirocin
D. Oral fluconazole
Answer and explanation
C. Intranasal mupirocin
Mupirocin ointment applied intranasally is a common component of targeted MRSA decolonisation. Chlorhexidine washes are often added for skin decolonisation in accordance with local protocols.
A. Oral vancomycin: Oral vancomycin acts principally within the intestine because systemic absorption is poor; it does not treat bloodstream infection.
B. Intravenous metronidazole: Intravenous metronidazole is not equivalent to preferred oral luminal therapy for nonfulminant C. difficile disease.
D. Oral fluconazole: Fluconazole treats susceptible fungal infection; it is not an anti-MRSA decolonising drug or a luminal C. difficile agent.
Exam pearl: Intranasal mupirocin — Decolonisation is not the same as treating MRSA bacteraemia.
Q107. A child has a tenacious grey pharyngeal membrane that bleeds when disturbed. Which organism should be suspected?
Recall paper: May 2022; Microbiology
A. Candida albicans
B. Corynebacterium diphtheriae
C. Streptococcus pneumoniae
D. Epstein–Barr virus
Answer and explanation
B. Corynebacterium diphtheriae
Toxigenic C. diphtheriae produces an adherent pseudomembrane, local tissue injury and potentially systemic myocarditis or neuropathy. Prompt airway assessment, antitoxin when indicated and antibiotic treatment are essential.
A. Candida albicans: Candida albicans is a yeast causing thrush and opportunistic mucosal or invasive candidiasis, rather than this syndrome.
C. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
D. Epstein–Barr virus: Epstein–Barr virus causes infectious mononucleosis and is linked to several lymphomas and nasopharyngeal carcinoma.
Exam pearl: Corynebacterium diphtheriae — Do not forcefully strip a suspected diphtheritic membrane
Q108. Which immunoglobulin mediates classic immediate peanut-triggered hypersensitivity?
Recall paper: May 2022; Immunology
A. IgG4 alone
B. IgM
C. IgA
D. IgE
Answer and explanation
D. IgE
Allergen-specific IgE bound to mast-cell Fc epsilon receptors triggers degranulation upon re-exposure, releasing histamine and other mediators. This produces rapid urticaria, bronchospasm or anaphylaxis.
A. IgG4 alone: IgG4 is not the major immunoglobulin mediating immediate mast-cell degranulation in type I allergy.
B. IgM: IgM concerns a different cell, inflammatory mechanism or immune component from the one directly implicated here.
C. IgA: IgA is chiefly involved in mucosal immunity rather than the classic mast-cell-linked immediate hypersensitivity response.
Exam pearl: IgE — Type I hypersensitivity is IgE mediated.
Q109. A preterm neonate has suspected pyogenic spondylodiscitis. Which bacterium is an important potential cause?
Recall paper: September 2022; Microbiology
A. Clostridioides difficile
B. Campylobacter jejuni
C. Bartonella henselae
D. Staphylococcus aureus
Answer and explanation
D. Staphylococcus aureus
S. aureus is an important cause of paediatric discitis and vertebral osteomyelitis; Kingella kingae is also noteworthy in younger children and may be difficult to culture. Age and vaccination status modify the differential.
A. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
B. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
C. Bartonella henselae: Bartonella henselae classically causes regional cat-scratch lymphadenopathy, not this condition.
Exam pearl: Staphylococcus aureus — Staphylococcus aureus is the classic general answer, but Kingella is important in young children.
Q110. How does Clostridium perfringens usually appear on Gram staining?
Recall paper: September 2022; Microbiology
A. Gram-negative diplococci
B. Gram-positive cocci in clusters
C. Gram-positive rods
D. Gram-negative curved bacilli
Answer and explanation
C. Gram-positive rods
C. perfringens is a large anaerobic Gram-positive bacillus capable of toxin-mediated soft-tissue infection. Sporulation may be difficult to demonstrate in tissue specimens.
A. Gram-negative diplococci: This staining and morphology pattern fits organisms such as Neisseria, rather than Gram-positive Clostridium rods.
B. Gram-positive cocci in clusters: Cocci in clusters suggest staphylococci, whereas the organism discussed is rod-shaped.
D. Gram-negative curved bacilli: Curved Gram-negative rods suggest Vibrio or Campylobacter, not this Gram-positive anaerobe.
Exam pearl: Gram-positive rods — Clostridium perfringens = anaerobic Gram-positive rod.
Q111. Several people develop vomiting two hours after a shared meal. Which pathogen causes classically rapid food poisoning through preformed toxin?
Recall paper: September 2022; Microbiology
A. Campylobacter jejuni
B. Salmonella Typhi
C. Staphylococcus aureus
D. Clostridioides difficile
Answer and explanation
C. Staphylococcus aureus
Staphylococcal enterotoxin formed in contaminated food can produce abrupt vomiting within about 1–6 hours of ingestion. Illness is usually self-limited and is treated with supportive fluids.
A. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
B. Salmonella Typhi: Salmonella Typhi causes enteric fever, generally a systemic febrile illness rather than the condition in this stem.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Vomiting within hours suggests preformed toxin.
Q112. A psoas-region abscess compresses a nerve supplying skin over the lateral thigh, producing burning paraesthesia. Which nerve is involved?
Recall paper: September 2022; Anatomy
A. Femoral nerve motor branches
B. Lateral femoral cutaneous nerve
C. Obturator nerve
D. Common fibular nerve
Answer and explanation
B. Lateral femoral cutaneous nerve
The lateral femoral cutaneous nerve arises from L2–L3 and runs close to the iliacus and anterior superior iliac spine before passing beneath or through the inguinal ligament. Compression causes meralgia paraesthetica without motor weakness.
A. Femoral nerve motor branches: Femoral nerve motor branches supplies or refers to a different anatomical region from the tissue or pathway described in the question.
C. Obturator nerve: Obturator nerve supplies or refers to a different anatomical region from the tissue or pathway described in the question.
D. Common fibular nerve: Common fibular nerve supplies or refers to a different anatomical region from the tissue or pathway described in the question.
Exam pearl: Lateral femoral cutaneous nerve — Pure lateral-thigh sensory loss without weakness suggests lateral femoral cutaneous neuropathy.
Q113. After catheterisation, the retracted foreskin cannot be replaced and the glans becomes swollen and painful. What is the diagnosis?
Recall paper: Paper/session not recorded in source; Urology
A. Paraphimosis
B. Phimosis
C. Balanitis
D. Balanoposthitis
Answer and explanation
A. Paraphimosis
Paraphimosis occurs when a retracted foreskin becomes trapped behind the glans, forming a constricting band and causing distal oedema. Urgent reduction is required to prevent vascular compromise.
B. Phimosis: Phimosis is a different pathological or clinical diagnosis, with a pattern distinct from the defining findings in this stem.
C. Balanitis: Balanitis is a different pathological or clinical diagnosis, with a pattern distinct from the defining findings in this stem.
D. Balanoposthitis: Balanoposthitis is a different pathological or clinical diagnosis, with a pattern distinct from the defining findings in this stem.
Exam pearl: Paraphimosis — Paraphimosis is an urgent reduction problem, not simply an inflamed foreskin.
Q114. A Meckel diverticulum receives arterial supply from a persistent branch of which artery?
Recall paper: Paper/session not recorded in source; Anatomy
A. Superior mesenteric artery
B. Inferior mesenteric artery
C. Coeliac trunk
D. Internal iliac artery
Answer and explanation
A. Superior mesenteric artery
The persistent vitelline artery supplying a Meckel diverticulum generally originates from the superior mesenteric arterial system. Meckel diverticulum is a true congenital diverticulum of the antimesenteric ileal border.
B. Inferior mesenteric artery: Inferior mesenteric artery supplies or refers to a different anatomical region from the tissue or pathway described in the question.
C. Coeliac trunk: The coeliac trunk supplies foregut derivatives, unlike the embryonic vitelline supply associated with the ileal diverticulum.
D. Internal iliac artery: Internal iliac artery supplies or refers to a different anatomical region from the tissue or pathway described in the question.
Exam pearl: Superior mesenteric artery — Meckel diverticulum is a midgut structure supplied by the SMA.
Q115. Which bloodborne viral hepatitis is classically associated with delayed post-transfusion hepatitis in historical recalls?
Recall paper: Paper/session not recorded in source; Microbiology
A. Hepatitis A virus
B. Rotavirus
C. Cytomegalovirus as the usual post-transfusion hepatitis cause
D. Hepatitis C virus
Answer and explanation
D. Hepatitis C virus
Hepatitis C caused much historical post-transfusion hepatitis before effective blood-donor screening. Modern screened blood makes this much less common; hepatitis B also has transfusion risk.
A. Hepatitis A virus: Hepatitis A virus causes faecal–oral acute hepatitis rather than this bacterial or parasitic disease.
B. Rotavirus: Rotavirus causes acute viral gastroenteritis, especially in children.
C. Cytomegalovirus as the usual post-transfusion hepatitis cause: Cytomegalovirus as the usual post-transfusion hepatitis cause concerns a different cell, inflammatory mechanism or immune component from the one directly implicated here.
Exam pearl: Hepatitis C virus — Historical post-transfusion hepatitis commonly refers to HCV
Q116. A small, highly vascular, friable red papule bleeds readily on contact. What benign lesion is classically described?
Recall paper: Paper/session not recorded in source; Pathology
A. Dermatofibroma
B. Pyogenic granuloma (lobular capillary haemangioma)
C. Seborrhoeic keratosis
D. Lipoma
Answer and explanation
B. Pyogenic granuloma (lobular capillary haemangioma)
Pyogenic granuloma is a benign lobular capillary proliferation that can arise after minor trauma or in pregnancy. It is typically red, friable and bleeds easily.
A. Dermatofibroma: A dermatofibroma is usually a firm benign cutaneous fibrohistiocytic nodule, not a friable bleeding vascular lesion.
C. Seborrhoeic keratosis: This benign epidermal lesion is often waxy and stuck-on, unlike a rapidly growing friable vascular papule.
D. Lipoma: A lipoma is a soft subcutaneous fatty tumour, not a bleeding superficial vascular proliferation.
Exam pearl: Pyogenic granuloma (lobular capillary haemangioma) — Pyogenic granuloma is a vascular lesion, not a pyogenic infection.
Q117. A child develops microangiopathic haemolysis, thrombocytopenia and acute kidney injury following diarrhoeal illness. Which pathogen is classically implicated?
Recall paper: Paper/session not recorded in source; Microbiology
A. Shiga toxin-producing Escherichia coli
B. Streptococcus pyogenes
C. Clostridioides difficile
D. Bacteroides fragilis
Answer and explanation
A. Shiga toxin-producing Escherichia coli
Shiga toxin-producing E. coli, classically O157:H7 or other toxin-producing strains, causes typical diarrhoea-associated haemolytic uraemic syndrome by endothelial injury. The key triad is haemolytic anaemia, thrombocytopenia and acute kidney injury.
B. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
C. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
D. Bacteroides fragilis: B. fragilis is a colonic anaerobe associated with intra-abdominal abscess, not the characteristic organism in this vignette.
Exam pearl: Shiga toxin-producing Escherichia coli — Haematuria after a sore throat alone is not sufficient to diagnose HUS
Q118. A patient with recurrent UTIs develops a branching staghorn renal calculus. Which bacterium is classically associated?
Recall paper: Paper/session not recorded in source; Microbiology
A. Escherichia coli
B. Staphylococcus epidermidis
C. Streptococcus pyogenes
D. Proteus mirabilis
Answer and explanation
D. Proteus mirabilis
Proteus mirabilis expresses urease, which splits urea into ammonia, increases urinary pH and promotes magnesium ammonium phosphate (struvite) and carbonate apatite crystallisation. Recurrent urease-producing urinary infection is associated with large branching calculi.
A. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
B. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
C. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
Exam pearl: Proteus mirabilis — Commonest UTI organism is E. coli
Q119. Which organism is most commonly associated with haematogenous native pyogenic vertebral osteomyelitis in adults?
Recall paper: Paper/session not recorded in source; Microbiology
A. Clostridioides difficile
B. Staphylococcus epidermidis
C. Staphylococcus aureus
D. Campylobacter jejuni
Answer and explanation
C. Staphylococcus aureus
Staphylococcus aureus is the leading cause of adult native vertebral osteomyelitis or pyogenic discitis. Blood cultures, inflammatory markers and MRI help establish the diagnosis and define the extent of infection.
A. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
B. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
Exam pearl: Staphylococcus aureus — Native pyogenic discitis = S. aureus until proved otherwise
Q120. What procedure provides the most useful definitive microbiological investigation for suspected septic arthritis?
Recall paper: January 2023; Clinical Surgery
A. Plain radiograph alone
B. Serum urate alone
C. Clinical observation without sampling
D. Urgent synovial aspiration for cell count, Gram stain and culture
Answer and explanation
D. Urgent synovial aspiration for cell count, Gram stain and culture
Arthrocentesis is central to diagnosing septic arthritis; synovial analysis includes white-cell count, differential, Gram stain and culture. Normal fever or peripheral WCC does not exclude septic arthritis.
A. Plain radiograph alone: Radiographs cannot confirm infection or distinguish septic arthritis reliably without joint-fluid assessment.
B. Serum urate alone: Serum urate can be normal in acute gout and does not establish or exclude joint infection.
C. Clinical observation without sampling: This omits necessary evaluation or infection control and does not address the clinical risk described.
Exam pearl: Urgent synovial aspiration for cell count, Gram stain and culture — Aspiration and culture, not normal peripheral white count, settles the infection question.
Q121. For a reusable arthroscope entering a normally sterile joint, which reprocessing endpoint should be aimed for?
Recall paper: January 2023; Microbiology
A. Simple alcohol wipe
B. Sterilisation using a validated compatible process
C. Low-level disinfection
D. Soap-and-water rinse alone
Answer and explanation
B. Sterilisation using a validated compatible process
Arthroscopes enter sterile tissue and are classified as critical instruments; sterilisation is recommended using the device-compatible validated process, often steam for heat-stable devices. High-level disinfection is not synonymous with sterilisation.
A. Simple alcohol wipe: Cleaning or low-level surface treatment alone is not a validated substitute for the required level of medical-device reprocessing.
C. Low-level disinfection: Low-level disinfection is reserved for noncritical equipment contacting intact skin, not semicritical or critical devices.
D. Soap-and-water rinse alone: Cleaning or low-level surface treatment alone is not a validated substitute for the required level of medical-device reprocessing.
Exam pearl: Sterilisation using a validated compatible process — An older recall naming glutaraldehyde as best sterilisation fails to distinguish disinfection from sterilisation.
Q122. Following major ileal resection, which nutritional issue particularly merits assessment?
Recall paper: January 2023; Physiology
A. Intrinsic factor excess
B. Malabsorption of bile salts and vitamin B12
C. Isolated increased colonic folate production
D. Complete nutritional normality regardless of bowel length
Answer and explanation
B. Malabsorption of bile salts and vitamin B12
The terminal ileum absorbs bile salts and vitamin B12; extensive resection can result in malabsorption, diarrhoea and nutritional deficiencies. Enteral nutrition is preferred where gut function is adequate, with parenteral support if absorptive capacity is insufficient.
A. Intrinsic factor excess: Intrinsic factor relates to vitamin B12 absorption, not the general nutritional support decisions following extensive intestinal resection.
C. Isolated increased colonic folate production: Microbial folate synthesis does not compensate for all malabsorptive risks after significant small-bowel resection.
D. Complete nutritional normality regardless of bowel length: Residual bowel length and ileal loss directly influence B12, bile salt, fluid and nutrient absorption.
Exam pearl: Malabsorption of bile salts and vitamin B12 — Do not prescribe TPN solely from bowel length without evaluating absorptive function.
Q123. The original recall is irretrievably fragmented and cannot be reconstructed reliably. What is the correct editorial action?
Recall paper: January 2023; Source Integrity
UNSCORED SOURCE HOLD: The original recall is insufficient to support a scored question.
Q124. Which hepatobiliary condition is strongly associated with ulcerative colitis?
Recall paper: January 2023; Pathology
A. Acute calculous cholecystitis
B. Primary sclerosing cholangitis
C. Haemochromatosis
D. Hepatitis A infection
Answer and explanation
B. Primary sclerosing cholangitis
Primary sclerosing cholangitis causes inflammatory fibrosis and multifocal stricturing of intra- and extrahepatic bile ducts. It is associated with inflammatory bowel disease, especially ulcerative colitis.
A. Acute calculous cholecystitis: This involves gallstones and inflammation; biliary strictures with ulcerative colitis point toward PSC.
C. Haemochromatosis: Iron overload typically causes cirrhosis, diabetes and skin pigmentation, not the characteristic multifocal cholangiographic strictures of PSC.
D. Hepatitis A infection: Hepatitis A infection concerns a different cell, inflammatory mechanism or immune component from the one directly implicated here.
Exam pearl: Primary sclerosing cholangitis — Ulcerative colitis + multifocal biliary strictures = PSC.
Q125. Which organism is most commonly associated with haematogenous native pyogenic vertebral osteomyelitis in adults?
Recall paper: January 2023; Microbiology
A. Clostridioides difficile
B. Staphylococcus aureus
C. Staphylococcus epidermidis
D. Campylobacter jejuni
Answer and explanation
B. Staphylococcus aureus
Staphylococcus aureus is the leading cause of adult native vertebral osteomyelitis or pyogenic discitis. Blood cultures, inflammatory markers and MRI help establish the diagnosis and define the extent of infection.
A. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
C. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
Exam pearl: Staphylococcus aureus — Native pyogenic discitis = S. aureus until proved otherwise
Q126. A child has otalgia and new purulent otorrhoea following an upper respiratory illness. Which statement about acute otitis media is accurate?
Recall paper: May 2023; Microbiology
A. Several bacteria can cause acute otitis media, including pneumococcus, nontypeable H. influenzae and Moraxella
B. Only Staphylococcus aureus causes it
C. It is invariably caused by Streptococcus intermedius
D. Bacterial aetiology can be confirmed by symptoms alone
Answer and explanation
A. Several bacteria can cause acute otitis media, including pneumococcus, nontypeable H. influenzae and Moraxella
Acute otitis media is commonly associated with Streptococcus pneumoniae, nontypeable Haemophilus influenzae and Moraxella catarrhalis. Symptoms alone do not distinguish the exact bacterium, and otorrhoea can occur after tympanic membrane perforation.
B. Only Staphylococcus aureus causes it: Staphylococcus can cause suppurative ear infection but is not the only cause of paediatric acute otitis media.
C. It is invariably caused by Streptococcus intermedius: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
D. Bacterial aetiology can be confirmed by symptoms alone: Clinical otalgia and otorrhoea cannot identify a specific bacterium without specimen testing.
Exam pearl: Several bacteria can cause acute otitis media, including pneumococcus, nontypeable H. influenzae and Moraxella — The source stem does not identify a unique organism, so a single pathogen answer would be unjustified.
Q127. A gardener develops painless nodules ascending along lymphatic channels weeks after a rose-thorn injury. What organism is most typical?
Recall paper: May 2023; Microbiology
A. Streptococcus pyogenes
B. Sporothrix schenckii complex
C. Staphylococcus aureus
D. Clostridium perfringens
Answer and explanation
B. Sporothrix schenckii complex
Sporothrix is a dimorphic environmental fungus causing subacute nodular lymphangitis after inoculation from plant matter. The original recall mentions a thorn but does not show the referenced photograph or indicate whether the lesions appeared over days or weeks.
A. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
C. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
D. Clostridium perfringens: Clostridium perfringens is associated with clostridial myonecrosis, not this organism-specific diagnosis.
Exam pearl: Sporothrix schenckii complex — Thorn-prick alone is nonspecific
Q128. Needle-shaped, strongly negatively birefringent crystals are seen in synovial fluid. What is the diagnosis?
Recall paper: May 2023; Pathology
A. Monosodium urate crystal arthritis (gout)
B. Calcium pyrophosphate crystal arthritis
C. Septic arthritis
D. Rheumatoid arthritis
Answer and explanation
A. Monosodium urate crystal arthritis (gout)
Monosodium urate forms needle-shaped negatively birefringent crystals under polarised light, supporting gout. Calcium pyrophosphate deposits form shorter rhomboid weakly positive birefringent crystals.
B. Calcium pyrophosphate crystal arthritis: Calcium pyrophosphate crystal arthritis is a different pathological or clinical diagnosis, with a pattern distinct from the defining findings in this stem.
C. Septic arthritis: Septic arthritis is a different pathological or clinical diagnosis, with a pattern distinct from the defining findings in this stem.
D. Rheumatoid arthritis: Rheumatoid arthritis is a different pathological or clinical diagnosis, with a pattern distinct from the defining findings in this stem.
Exam pearl: Monosodium urate crystal arthritis (gout) — Do not mistake gout crystals for pyrophosphate crystals.
Q129. How is an uncomplicated elective cholecystectomy with controlled entry into the biliary tract normally classified?
Recall paper: May 2023; Clinical Surgery
A. Clean
B. Dirty or infected
C. Clean-contaminated
D. Contaminated from uncontrolled gross spillage
Answer and explanation
C. Clean-contaminated
Clean-contaminated surgery involves controlled entry into a colonised tract such as the biliary or alimentary tract without unusual contamination. If gross spillage or infection occurs, the wound class changes.
A. Clean: Entry into the biliary tract makes an uncomplicated cholecystectomy a clean-contaminated rather than a clean wound.
B. Dirty or infected: This requires established infection, devitalised tissue or perforated viscus, not routine controlled biliary entry.
D. Contaminated from uncontrolled gross spillage: A routine cholecystectomy without major spillage is generally clean-contaminated, not contaminated.
Exam pearl: Clean-contaminated — Controlled entry into biliary tract = class II clean-contaminated.
Q130. Which drug has useful activity against many clinically important anaerobes of the Bacteroides fragilis group?
Recall paper: May 2023; Microbiology
A. Flucloxacillin alone
B. Gentamicin monotherapy
C. Cefazolin monotherapy
D. Metronidazole
Answer and explanation
D. Metronidazole
Metronidazole is active against many obligate anaerobic bacteria, including B. fragilis group organisms. For polymicrobial abdominal infection it is combined with drugs active against aerobic Gram-negative organisms as needed.
A. Flucloxacillin alone: Flucloxacillin alone has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
B. Gentamicin monotherapy: Gentamicin monotherapy lacks suitable standalone coverage for many mixed or Gram-positive deep infections and carries renal/ototoxic risk.
C. Cefazolin monotherapy: Cefazolin lacks reliable anaerobic bowel coverage and is inadequate alone for many complicated intra-abdominal infections.
Exam pearl: Metronidazole — Metronidazole provides anaerobic cover but not complete Gram-negative aerobic cover.
Q131. Vancomycin belongs to which antimicrobial class?
Recall paper: May 2023; Microbiology
A. Beta-lactams
B. Macrolides
C. Glycopeptides
D. Fluoroquinolones
Answer and explanation
C. Glycopeptides
Vancomycin is a glycopeptide that inhibits Gram-positive bacterial cell-wall synthesis by binding D-Ala–D-Ala termini of peptidoglycan precursors. Intravenous therapy is used for systemic infections; oral administration primarily treats intestinal C. difficile.
A. Beta-lactams: Beta-lactams has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
B. Macrolides: Macrolides has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
D. Fluoroquinolones: Fluoroquinolones has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
Exam pearl: Glycopeptides — Vancomycin = glycopeptide.
Q132. An inpatient develops profuse diarrhoea and colonic pseudomembranes after antimicrobial treatment. Which pathogen is responsible?
Recall paper: May 2023; Microbiology
A. Clostridioides difficile
B. Campylobacter jejuni
C. Shigella dysenteriae
D. Clostridium perfringens
Answer and explanation
A. Clostridioides difficile
Antibiotic disruption of the gut microbiota permits toxin-producing C. difficile proliferation. Toxins A and B produce epithelial injury, inflammation and pseudomembranous colitis.
B. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
C. Shigella dysenteriae: Shigella dysenteriae causes invasive bacillary dysentery and can produce Shiga toxin.
D. Clostridium perfringens: Clostridium perfringens is associated with clostridial myonecrosis, not this organism-specific diagnosis.
Exam pearl: Clostridioides difficile — Do not treat a positive colonisation test without compatible clinical illness.
Q133. A Proteus-positive patient has an alkaline urine and a large staghorn calculus. What is the classic stone composition?
Recall paper: May 2023; Microbiology
A. Magnesium ammonium phosphate (struvite)
B. Calcium oxalate
C. Uric acid
D. Cystine
Answer and explanation
A. Magnesium ammonium phosphate (struvite)
Urease splits urea to ammonia and alkalinises urine, promoting magnesium ammonium phosphate hexahydrate crystallisation. Infection stones can rapidly enlarge to form staghorn renal calculi.
B. Calcium oxalate: Calcium oxalate is a common noninfection urinary stone without the specific urease-driven alkaline mechanism.
C. Uric acid: Uric acid forms particularly in acidic urine, unlike an alkaline infection-related struvite calculus.
D. Cystine: Cystine occurs with hereditary cystinuria rather than urease-producing urinary infection.
Exam pearl: Magnesium ammonium phosphate (struvite) — Struvite = MgNH4PO4 associated with urease-positive urinary infection.
Q134. A child has febrile right iliac fossa pain and mesenteric adenitis after exposure to pigs, with a normal appendix. Which organism is characteristic?
Recall paper: May 2023; Microbiology
A. Staphylococcus aureus
B. Clostridioides difficile
C. Yersinia enterocolitica
D. Bordetella pertussis
Answer and explanation
C. Yersinia enterocolitica
Y. enterocolitica may cause ileitis and mesenteric adenitis, presenting as pseudoappendicitis. Exposure to pigs and contaminated pork is an important epidemiological clue.
A. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
B. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
D. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
Exam pearl: Yersinia enterocolitica — Pig exposure + mesenteric adenitis + normal appendix = Yersinia.
Q135. How should a flexible endoscope that contacts intact gastrointestinal mucosa be reprocessed at minimum?
Recall paper: May 2023; Microbiology
A. Thorough cleaning followed by high-level disinfection
B. Brief alcohol wiping alone
C. Low-level disinfection
D. Routine dry-heat sterilisation regardless of instrument compatibility
Answer and explanation
A. Thorough cleaning followed by high-level disinfection
Flexible GI endoscopes are Spaulding semicritical devices because they contact mucosa without normally entering sterile tissue. They require meticulous channel cleaning and at least high-level disinfection according to validated manufacturer instructions.
B. Brief alcohol wiping alone: Cleaning or low-level surface treatment alone is not a validated substitute for the required level of medical-device reprocessing.
C. Low-level disinfection: Low-level disinfection is reserved for noncritical equipment contacting intact skin, not semicritical or critical devices.
D. Routine dry-heat sterilisation regardless of instrument compatibility: The proposed reprocessing choice ignores the equipment classification or heat sensitivity; use an appropriate validated method.
Exam pearl: Thorough cleaning followed by high-level disinfection — A specific chemical named in a historical recall is not universally the “best” method
Q136. Which fastidious Gram-negative organism is characteristic of infected human bite wounds?
Recall paper: January 2024; Microbiology
A. Pasteurella multocida
B. Bartonella henselae
C. Eikenella corrodens
D. Clostridium tetani
Answer and explanation
C. Eikenella corrodens
Eikenella corrodens is a constituent of human oral flora and can infect clenched-fist injuries or other human bite wounds. Such wounds may penetrate joints or tendon sheaths despite small skin openings.
A. Pasteurella multocida: Pasteurella multocida is associated with rapidly progressive animal-bite infection, especially cat bites.
B. Bartonella henselae: Bartonella henselae classically causes regional cat-scratch lymphadenopathy, not this condition.
D. Clostridium tetani: Clostridium tetani produces tetanospasmin, causing spastic paralysis rather than this manifestation.
Exam pearl: Eikenella corrodens — Fight-bite injury = suspect Eikenella and deep structural penetration.
Q137. A patient with infective endocarditis has a reported penicillin allergy, but the isolate and allergy phenotype are unspecified. Which statement is safest?
Recall paper: January 2024; Microbiology
A. Gentamicin alone is standard definitive therapy
B. Cefuroxime is always contraindicated
C. Definitive antibiotics depend on organism, sensitivities and allergy assessment
D. Penicillin allergy can be ignored
Answer and explanation
C. Definitive antibiotics depend on organism, sensitivities and allergy assessment
Endocarditis regimens depend on the cultured organism, valve type, susceptibility and whether allergy is immediate or delayed. Gentamicin monotherapy is not adequate treatment for most endocarditis syndromes and can be nephrotoxic.
A. Gentamicin alone is standard definitive therapy: Gentamicin alone is standard definitive therapy has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
B. Cefuroxime is always contraindicated: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
D. Penicillin allergy can be ignored: This omits necessary evaluation or infection control and does not address the clinical risk described.
Exam pearl: Definitive antibiotics depend on organism, sensitivities and allergy assessment — No universal replacement antibiotic can be selected from the words “penicillin allergy” alone.
Q138. Tender ascending red streaks develop from a recent skin puncture. What is the classic pathogen?
Recall paper: January 2024; Microbiology
A. Staphylococcus epidermidis
B. Streptococcus pyogenes
C. Escherichia coli
D. Sporothrix schenckii
Answer and explanation
B. Streptococcus pyogenes
Group A beta-haemolytic streptococci commonly cause rapidly advancing nonpurulent cellulitis and lymphangitis. The tender proximal erythematous streaks reflect inflammation of superficial lymphatic vessels.
A. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
C. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
D. Sporothrix schenckii: Sporothrix causes delayed nodular lymphangitis following plant inoculation, rather than an acute red streak within 24–48 hours.
Exam pearl: Streptococcus pyogenes — Plant-thorn history alone does not prove sporotrichosis
Q139. A psoas-region abscess compresses a nerve supplying skin over the lateral thigh, producing burning paraesthesia. Which nerve is involved?
Recall paper: January 2024; Anatomy
A. Lateral femoral cutaneous nerve
B. Femoral nerve motor branches
C. Obturator nerve
D. Common fibular nerve
Answer and explanation
A. Lateral femoral cutaneous nerve
The lateral femoral cutaneous nerve arises from L2–L3 and runs close to the iliacus and anterior superior iliac spine before passing beneath or through the inguinal ligament. Compression causes meralgia paraesthetica without motor weakness.
B. Femoral nerve motor branches: Femoral nerve motor branches supplies or refers to a different anatomical region from the tissue or pathway described in the question.
C. Obturator nerve: Obturator nerve supplies or refers to a different anatomical region from the tissue or pathway described in the question.
D. Common fibular nerve: Common fibular nerve supplies or refers to a different anatomical region from the tissue or pathway described in the question.
Exam pearl: Lateral femoral cutaneous nerve — Pure lateral-thigh sensory loss without weakness suggests lateral femoral cutaneous neuropathy.
Q140. A patient has laboratory-supported invasive Entamoeba histolytica colitis with bloody diarrhoea. Which drug treats the invasive tissue stage?
Recall paper: January 2024; Microbiology
A. Metronidazole
B. Mebendazole
C. Penicillin V
D. Vancomycin
Answer and explanation
A. Metronidazole
Metronidazole treats invasive amoebic infection by acting on trophozoites in tissues. It must be followed by a luminal amoebicide where available to eradicate cyst carriage and prevent relapse.
B. Mebendazole: Mebendazole is an antihelminthic effective against intestinal nematodes such as pinworm, not the process in this question.
C. Penicillin V: Penicillin V may be used for asplenia prophylaxis or susceptible streptococci but not for this particular indication.
D. Vancomycin: Vancomycin is a glycopeptide used systemically against serious susceptible Gram-positive infections and orally for C. difficile.
Exam pearl: Metronidazole — Metronidazole alone does not reliably eliminate intestinal luminal cysts.
Q141. For recurrent otitis externa with obstructing debris, what local management is useful to permit topical therapy?
Recall paper: January 2024; Microbiology
A. Aural toilet with appropriately selected topical treatment
B. Routine oral vancomycin
C. Immediate tonsillectomy
D. No inspection of the external canal
Answer and explanation
A. Aural toilet with appropriately selected topical treatment
Otitis externa commonly responds to careful ear-canal cleaning where appropriate and topical antimicrobial or acidifying therapy, sometimes with topical steroid. Selection depends on tympanic membrane integrity, microbiology, severity and contraindications.
B. Routine oral vancomycin: Routine oral vancomycin has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
C. Immediate tonsillectomy: Surgical tonsil removal is not the first step for suspected acute diphtheria or supraglottic airway compromise.
D. No inspection of the external canal: This omits necessary evaluation or infection control and does not address the clinical risk described.
Exam pearl: Aural toilet with appropriately selected topical treatment — Recurrent otitis externa differs from acute otitis media
Q142. An immunocompromised patient develops chronic weight loss, cough and haemoptysis, raising concern for tuberculosis. Which organism must be excluded?
Recall paper: January 2024; Microbiology
A. Staphylococcus epidermidis
B. Enterobius vermicularis
C. Bartonella henselae
D. Mycobacterium tuberculosis
Answer and explanation
D. Mycobacterium tuberculosis
Pulmonary tuberculosis is caused by M. tuberculosis and may produce chronic constitutional symptoms, cavitation and haemoptysis. In HIV-associated advanced immunosuppression, imaging may be atypical or disseminated rather than apical.
A. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
B. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
C. Bartonella henselae: Bartonella henselae classically causes regional cat-scratch lymphadenopathy, not this condition.
Exam pearl: Mycobacterium tuberculosis — Steroids plus weight loss and haemoptysis should trigger a TB evaluation.
Q143. Which vaccine combination specifically targets major encapsulated bacteria in asplenic patients?
Recall paper: September 2024; Microbiology
A. BCG alone
B. Hepatitis A vaccine alone
C. Pneumococcal, meningococcal and Hib vaccination
D. Rotavirus vaccine alone
Answer and explanation
C. Pneumococcal, meningococcal and Hib vaccination
Splenectomy increases susceptibility to rapidly progressive infection by encapsulated pathogens, notably S. pneumoniae, N. meningitidis and H. influenzae type b. Vaccinate according to current age- and history-based schedules.
A. BCG alone: BCG protects primarily against severe tuberculosis in childhood and does not replace encapsulated-bacterium vaccines.
B. Hepatitis A vaccine alone: Hepatitis A vaccine alone concerns a different cell, inflammatory mechanism or immune component from the one directly implicated here.
D. Rotavirus vaccine alone: Rotavirus vaccination prevents selected gastroenteritis outcomes, not invasive pneumococcal or meningococcal disease.
Exam pearl: Pneumococcal, meningococcal and Hib vaccination — Vaccination lowers but does not eliminate overwhelming post-splenectomy infection risk.
Q144. Which fastidious Gram-negative organism is characteristic of infected human bite wounds?
Recall paper: September 2024; Microbiology
A. Pasteurella multocida
B. Eikenella corrodens
C. Bartonella henselae
D. Clostridium tetani
Answer and explanation
B. Eikenella corrodens
Eikenella corrodens is a constituent of human oral flora and can infect clenched-fist injuries or other human bite wounds. Such wounds may penetrate joints or tendon sheaths despite small skin openings.
A. Pasteurella multocida: Pasteurella multocida is associated with rapidly progressive animal-bite infection, especially cat bites.
C. Bartonella henselae: Bartonella henselae classically causes regional cat-scratch lymphadenopathy, not this condition.
D. Clostridium tetani: Clostridium tetani produces tetanospasmin, causing spastic paralysis rather than this manifestation.
Exam pearl: Eikenella corrodens — Fight-bite injury = suspect Eikenella and deep structural penetration.
Q145. Which antihypertensive drug class may increase serum calcium?
Recall paper: September 2024; Pharmacology
A. Loop diuretics
B. Thiazide diuretics
C. Beta-blockers
D. ACE inhibitors
Answer and explanation
B. Thiazide diuretics
Thiazide diuretics increase renal distal-tubule calcium reabsorption and can raise serum calcium or unmask underlying hyperparathyroidism. Loop diuretics generally increase urinary calcium excretion.
A. Loop diuretics: Loop diuretics increase urinary calcium excretion, unlike thiazides which can raise serum calcium.
C. Beta-blockers: Beta-blockers lower heart rate and blood pressure but are not a typical drug cause of hypercalcaemia.
D. ACE inhibitors: ACE inhibitors target the renin–angiotensin system and are not typical causes of hypercalcaemia.
Exam pearl: Thiazide diuretics — Thiazides retain calcium
Q146. A breastfeeding woman develops tender erythema and a fluctuant breast collection. What organism is a frequent cause?
Recall paper: September 2024; Microbiology
A. Streptococcus pneumoniae
B. Enterococcus faecalis
C. Clostridium difficile
D. Staphylococcus aureus
Answer and explanation
D. Staphylococcus aureus
S. aureus is a common cause of lactational mastitis and associated breast abscess. Ultrasound is useful when an abscess is suspected, with drainage and appropriate antibiotics according to clinical assessment.
A. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
B. Enterococcus faecalis: Enterococcus faecalis may cause urinary or endovascular infection but is not the most characteristic answer here.
C. Clostridium difficile: Clostridium difficile is the former name of C. difficile, a cause of antibiotic-associated colitis rather than this presentation.
Exam pearl: Staphylococcus aureus — Lactational abscess = frequently S. aureus
Q147. A breastfeeding woman develops tender erythema and a fluctuant breast collection. What organism is a frequent cause?
Recall paper: April 2025; Microbiology
A. Streptococcus pneumoniae
B. Enterococcus faecalis
C. Clostridium difficile
D. Staphylococcus aureus
Answer and explanation
D. Staphylococcus aureus
S. aureus is a common cause of lactational mastitis and associated breast abscess. Ultrasound is useful when an abscess is suspected, with drainage and appropriate antibiotics according to clinical assessment.
A. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
B. Enterococcus faecalis: Enterococcus faecalis may cause urinary or endovascular infection but is not the most characteristic answer here.
C. Clostridium difficile: Clostridium difficile is the former name of C. difficile, a cause of antibiotic-associated colitis rather than this presentation.
Exam pearl: Staphylococcus aureus — Lactational abscess = frequently S. aureus
Q148. Several people develop vomiting two hours after a shared meal. Which pathogen causes classically rapid food poisoning through preformed toxin?
Recall paper: April 2025; Microbiology
A. Campylobacter jejuni
B. Salmonella Typhi
C. Clostridioides difficile
D. Staphylococcus aureus
Answer and explanation
D. Staphylococcus aureus
Staphylococcal enterotoxin formed in contaminated food can produce abrupt vomiting within about 1–6 hours of ingestion. Illness is usually self-limited and is treated with supportive fluids.
A. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
B. Salmonella Typhi: Salmonella Typhi causes enteric fever, generally a systemic febrile illness rather than the condition in this stem.
C. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Vomiting within hours suggests preformed toxin.
Q149. A child develops microangiopathic haemolysis, thrombocytopenia and acute kidney injury following diarrhoeal illness. Which pathogen is classically implicated?
Recall paper: April 2025; Microbiology
A. Streptococcus pyogenes
B. Shiga toxin-producing Escherichia coli
C. Clostridioides difficile
D. Bacteroides fragilis
Answer and explanation
B. Shiga toxin-producing Escherichia coli
Shiga toxin-producing E. coli, classically O157:H7 or other toxin-producing strains, causes typical diarrhoea-associated haemolytic uraemic syndrome by endothelial injury. The key triad is haemolytic anaemia, thrombocytopenia and acute kidney injury.
A. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
C. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
D. Bacteroides fragilis: B. fragilis is a colonic anaerobe associated with intra-abdominal abscess, not the characteristic organism in this vignette.
Exam pearl: Shiga toxin-producing Escherichia coli — Haematuria after a sore throat alone is not sufficient to diagnose HUS
Q150. A patient develops fever, abdominal pain and bloody diarrhoea after undercooked poultry. Which pathogen is classically involved?
Recall paper: April 2025; Microbiology
A. Staphylococcus aureus
B. Clostridioides difficile
C. Bordetella pertussis
D. Campylobacter jejuni
Answer and explanation
D. Campylobacter jejuni
Campylobacter jejuni is a curved, motile, Gram-negative organism transmitted especially through contaminated poultry. It causes inflammatory gastroenteritis and can cause ileocolitis resembling an acute surgical abdomen.
A. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
B. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
C. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
Exam pearl: Campylobacter jejuni — Campylobacter is a curved bacillus, not a flagellated diplococcus as one corrupted recall claims.
Q151. A contaminated traumatic wound rapidly develops malodour, gas and extensive muscle necrosis. What is the essential management principle?
Recall paper: April 2025; Microbiology
A. Topical antiseptic alone
B. Urgent surgical debridement plus broad-spectrum antibiotics
C. Delay surgery until all cultures return
D. Oral doxycycline monotherapy
Answer and explanation
B. Urgent surgical debridement plus broad-spectrum antibiotics
Clostridial myonecrosis and necrotising wound infection are surgical emergencies requiring immediate exploration and radical debridement. Empirical antimicrobials must cover Gram-positive, Gram-negative and anaerobic organisms, then be refined by cultures; targeted clostridial therapy usually includes penicillin plus clindamycin.
A. Topical antiseptic alone: Surface antisepsis cannot provide definitive therapy for deep established infection or replace necessary systemic therapy and source control.
C. Delay surgery until all cultures return: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
D. Oral doxycycline monotherapy: Doxycycline alone may lack the anaerobic or Gram-negative breadth necessary for necrotising or mixed traumatic infection.
Exam pearl: Urgent surgical debridement plus broad-spectrum antibiotics — No antibiotic substitutes for prompt surgical source control.
Q152. A Meckel diverticulum receives arterial supply from a persistent branch of which artery?
Recall paper: April 2026; Anatomy
A. Inferior mesenteric artery
B. Coeliac trunk
C. Superior mesenteric artery
D. Internal iliac artery
Answer and explanation
C. Superior mesenteric artery
The persistent vitelline artery supplying a Meckel diverticulum generally originates from the superior mesenteric arterial system. Meckel diverticulum is a true congenital diverticulum of the antimesenteric ileal border.
A. Inferior mesenteric artery: Inferior mesenteric artery supplies or refers to a different anatomical region from the tissue or pathway described in the question.
B. Coeliac trunk: The coeliac trunk supplies foregut derivatives, unlike the embryonic vitelline supply associated with the ileal diverticulum.
D. Internal iliac artery: Internal iliac artery supplies or refers to a different anatomical region from the tissue or pathway described in the question.
Exam pearl: Superior mesenteric artery — Meckel diverticulum is a midgut structure supplied by the SMA.
Q153. Which facultative Gram-negative organism is a common member of enteric flora encountered in appendicitis?
Recall paper: April 2026; Microbiology
A. Staphylococcus epidermidis
B. Clostridioides difficile
C. Escherichia coli
D. Corynebacterium diphtheriae
Answer and explanation
C. Escherichia coli
The appendix harbours polymicrobial enteric flora. Escherichia coli is a common aerobic or facultative Gram-negative organism, while Bacteroides fragilis-group organisms represent important anaerobes, particularly in complicated disease.
A. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
B. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
D. Corynebacterium diphtheriae: Corynebacterium diphtheriae produces pharyngeal pseudomembranes and an exotoxin associated with myocarditis and neuropathy.
Exam pearl: Escherichia coli — E. coli is a common enteric component
Q154. A household develops nocturnal pruritus ani and characteristic eggs on the perianal tape test. Which helminth is implicated?
Recall paper: April 2026; Microbiology
A. Ascaris lumbricoides
B. Trichinella spiralis
C. Enterobius vermicularis
D. Schistosoma haematobium
Answer and explanation
C. Enterobius vermicularis
Enterobius vermicularis is a nematode that deposits ova around the anus at night, provoking itching and household transmission. Diagnosis is commonly made using an early-morning adhesive-tape sample.
A. Ascaris lumbricoides: Ascaris lumbricoides is an intestinal nematode associated with obstruction or biliary migration in heavy infection.
B. Trichinella spiralis: Trichinella spiralis is acquired from infected meat and can cause myalgia, periorbital oedema and eosinophilia.
D. Schistosoma haematobium: Schistosoma haematobium produces urinary schistosomiasis, haematuria and increased squamous bladder-cancer risk.
Exam pearl: Enterobius vermicularis — Pinworm = nighttime perianal itch + adhesive-tape eggs.
Q155. Which CSF white-cell pattern is typical of acute pyogenic bacterial meningitis?
Recall paper: Paper/session not recorded in source; Microbiology
A. Marked eosinophilia
B. Pure basophilia
C. Lymphocytes exclusively in all cases
D. Neutrophilic predominance
Answer and explanation
D. Neutrophilic predominance
Acute bacterial meningitis usually causes neutrophil-rich CSF with raised protein and reduced CSF-to-serum glucose ratio. Prior antibiotics or organism-specific factors can alter the picture.
A. Marked eosinophilia: Eosinophilic CSF points toward selected parasites or nonstandard meningitis patterns, not usual acute bacterial meningitis.
B. Pure basophilia: Basophils are not the predominant CSF cell type in typical acute bacterial meningitis.
C. Lymphocytes exclusively in all cases: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
Exam pearl: Neutrophilic predominance — Pyogenic meningitis classically produces polymorphonuclear CSF predominance.
Q156. Which organ converts circulating lactate to glucose as part of the Cori cycle?
Recall paper: Paper/session not recorded in source; Physiology
A. Lung
B. Bone
C. Spleen
D. Liver
Answer and explanation
D. Liver
In the Cori cycle, lactate generated by anaerobic glycolysis in skeletal muscle and erythrocytes is converted into glucose by hepatic gluconeogenesis. Glucose can then re-enter peripheral circulation.
A. Lung: The lungs perform gas exchange, not the dominant hepatic conversion of lactate back to glucose.
B. Bone: Bone serves structural and mineral-homeostasis functions, not the principal Cori-cycle glucose-regeneration pathway.
C. Spleen: The spleen filters blood and mounts immune responses; it is not a major gluconeogenic organ.
Exam pearl: Liver — Cori cycle: lactate to liver, glucose back to peripheral tissues.
Q157. Which skin finding is characteristic of polyarteritis nodosa?
Recall paper: Paper/session not recorded in source; Pathology
A. Livedo reticularis
B. Koebner phenomenon
C. Target lesions of erythema multiforme
D. Dermatomal vesicular rash
Answer and explanation
A. Livedo reticularis
Polyarteritis nodosa is a necrotising medium-vessel vasculitis that may produce livedo reticularis, tender nodules, ulcers, neuropathy and visceral ischaemia. Clinical and tissue or angiographic evidence guide diagnosis.
B. Koebner phenomenon: Koebnerisation is lesion development after trauma, not the hallmark vascular skin morphology of polyarteritis nodosa.
C. Target lesions of erythema multiforme: Target lesions of erythema multiforme is a different morphological finding and is not the distinctive clinical feature requested.
D. Dermatomal vesicular rash: Dermatomal vesicular rash is a different morphological finding and is not the distinctive clinical feature requested.
Exam pearl: Livedo reticularis — PAN = medium-vessel vasculitis, livedo and mononeuritis multiplex.
Q158. The original recall is irretrievably fragmented and cannot be reconstructed reliably. What is the correct editorial action?
Recall paper: January 2026; Source Integrity
UNSCORED SOURCE HOLD: The original recall is insufficient to support a scored question.
Q159. A patient with sickle-cell disease develops osteomyelitis. Which bacterium has a particularly well-known association?
Recall paper: May 2024; Microbiology
A. Clostridioides difficile
B. Streptococcus pyogenes
C. Salmonella species
D. Neisseria meningitidis
Answer and explanation
C. Salmonella species
Sickle-cell disease predisposes to Salmonella osteomyelitis, probably through intestinal vaso-occlusion, transient bacteraemia and bone infarction. Staphylococcus aureus remains a common cause, so the exact wording “classically associated” matters.
A. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
B. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
D. Neisseria meningitidis: Neisseria meningitidis is a Gram-negative diplococcus causing meningococcal meningitis and sepsis.
Exam pearl: Salmonella species — Sickle-cell osteomyelitis: Salmonella is the classic examination association.
Q160. A breastfeeding woman develops tender erythema and a fluctuant breast collection. What organism is a frequent cause?
Recall paper: May 2024; Microbiology
A. Streptococcus pneumoniae
B. Enterococcus faecalis
C. Clostridium difficile
D. Staphylococcus aureus
Answer and explanation
D. Staphylococcus aureus
S. aureus is a common cause of lactational mastitis and associated breast abscess. Ultrasound is useful when an abscess is suspected, with drainage and appropriate antibiotics according to clinical assessment.
A. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
B. Enterococcus faecalis: Enterococcus faecalis may cause urinary or endovascular infection but is not the most characteristic answer here.
C. Clostridium difficile: Clostridium difficile is the former name of C. difficile, a cause of antibiotic-associated colitis rather than this presentation.
Exam pearl: Staphylococcus aureus — Lactational abscess = frequently S. aureus
Q161. Which organism is most commonly associated with haematogenous native pyogenic vertebral osteomyelitis in adults?
Recall paper: May 2024; Microbiology
A. Clostridioides difficile
B. Staphylococcus epidermidis
C. Staphylococcus aureus
D. Campylobacter jejuni
Answer and explanation
C. Staphylococcus aureus
Staphylococcus aureus is the leading cause of adult native vertebral osteomyelitis or pyogenic discitis. Blood cultures, inflammatory markers and MRI help establish the diagnosis and define the extent of infection.
A. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
B. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
Exam pearl: Staphylococcus aureus — Native pyogenic discitis = S. aureus until proved otherwise
Q162. Which immune process coats bacteria to improve recognition and engulfment by phagocytes?
Recall paper: May 2024; Immunology
A. Apoptosis
B. Chemotaxis alone
C. Opsonisation
D. Complement-mediated membrane attack alone
Answer and explanation
C. Opsonisation
Opsonisation deposits opsonins such as IgG and C3b on microbial surfaces, allowing efficient binding to phagocyte Fc and complement receptors. This enhances uptake and killing.
A. Apoptosis: Apoptosis describes regulated cell death rather than coating pathogens to enhance phagocytic uptake.
B. Chemotaxis alone: Chemotaxis recruits immune cells along chemical gradients but does not itself coat bacteria for receptor binding.
D. Complement-mediated membrane attack alone: Membrane attack complexes lyse susceptible organisms rather than performing the opsonin-tagging step asked.
Exam pearl: Opsonisation — Opsonins = IgG and C3b
Q163. A patient develops a deep intra-abdominal infection following perforated appendicitis. Which flora are typically implicated?
Recall paper: January 2025; Microbiology
A. Streptococcus pneumoniae alone
B. Bordetella pertussis alone
C. Staphylococcus epidermidis alone
D. Enteric Gram-negative organisms and anaerobes
Answer and explanation
D. Enteric Gram-negative organisms and anaerobes
Perforation releases bowel organisms including E. coli and anaerobic species such as Bacteroides fragilis group. Superficial incisional infection may be due to skin flora, but deep organ-space infection is commonly polymicrobial.
A. Streptococcus pneumoniae alone: Pneumococcus can cause invasive infection but cannot alone account for the usual mixed flora of this deep abscess.
B. Bordetella pertussis alone: A single respiratory pathogen cannot account for an infection that is usually polymicrobial or involves a different tissue.
C. Staphylococcus epidermidis alone: Coagulase-negative staphylococci can infect devices, but this clinical syndrome cannot be assumed to arise from that organism alone.
Exam pearl: Enteric Gram-negative organisms and anaerobes — Distinguish superficial incisional SSI from an intra-abdominal abscess after appendicectomy.
Q164. An immunocompromised patient develops chronic weight loss, cough and haemoptysis, raising concern for tuberculosis. Which organism must be excluded?
Recall paper: January 2025; Microbiology
A. Staphylococcus epidermidis
B. Mycobacterium tuberculosis
C. Enterobius vermicularis
D. Bartonella henselae
Answer and explanation
B. Mycobacterium tuberculosis
Pulmonary tuberculosis is caused by M. tuberculosis and may produce chronic constitutional symptoms, cavitation and haemoptysis. In HIV-associated advanced immunosuppression, imaging may be atypical or disseminated rather than apical.
A. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
C. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
D. Bartonella henselae: Bartonella henselae classically causes regional cat-scratch lymphadenopathy, not this condition.
Exam pearl: Mycobacterium tuberculosis — Steroids plus weight loss and haemoptysis should trigger a TB evaluation.
Q165. A child has a tenacious grey pharyngeal membrane that bleeds when disturbed. Which organism should be suspected?
Recall paper: January 2025; Microbiology
A. Candida albicans
B. Streptococcus pneumoniae
C. Corynebacterium diphtheriae
D. Epstein–Barr virus
Answer and explanation
C. Corynebacterium diphtheriae
Toxigenic C. diphtheriae produces an adherent pseudomembrane, local tissue injury and potentially systemic myocarditis or neuropathy. Prompt airway assessment, antitoxin when indicated and antibiotic treatment are essential.
A. Candida albicans: Candida albicans is a yeast causing thrush and opportunistic mucosal or invasive candidiasis, rather than this syndrome.
B. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
D. Epstein–Barr virus: Epstein–Barr virus causes infectious mononucleosis and is linked to several lymphomas and nasopharyngeal carcinoma.
Exam pearl: Corynebacterium diphtheriae — Do not forcefully strip a suspected diphtheritic membrane
Q166. How does Clostridium perfringens usually appear on Gram staining?
Recall paper: January 2025; Microbiology
A. Gram-positive rods
B. Gram-negative diplococci
C. Gram-positive cocci in clusters
D. Gram-negative curved bacilli
Answer and explanation
A. Gram-positive rods
C. perfringens is a large anaerobic Gram-positive bacillus capable of toxin-mediated soft-tissue infection. Sporulation may be difficult to demonstrate in tissue specimens.
B. Gram-negative diplococci: This staining and morphology pattern fits organisms such as Neisseria, rather than Gram-positive Clostridium rods.
C. Gram-positive cocci in clusters: Cocci in clusters suggest staphylococci, whereas the organism discussed is rod-shaped.
D. Gram-negative curved bacilli: Curved Gram-negative rods suggest Vibrio or Campylobacter, not this Gram-positive anaerobe.
Exam pearl: Gram-positive rods — Clostridium perfringens = anaerobic Gram-positive rod.
Q167. A child has a tenacious grey pharyngeal membrane that bleeds when disturbed. Which organism should be suspected?
Recall paper: January 2025; Microbiology
A. Candida albicans
B. Corynebacterium diphtheriae
C. Streptococcus pneumoniae
D. Epstein–Barr virus
Answer and explanation
B. Corynebacterium diphtheriae
Toxigenic C. diphtheriae produces an adherent pseudomembrane, local tissue injury and potentially systemic myocarditis or neuropathy. Prompt airway assessment, antitoxin when indicated and antibiotic treatment are essential.
A. Candida albicans: Candida albicans is a yeast causing thrush and opportunistic mucosal or invasive candidiasis, rather than this syndrome.
C. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
D. Epstein–Barr virus: Epstein–Barr virus causes infectious mononucleosis and is linked to several lymphomas and nasopharyngeal carcinoma.
Exam pearl: Corynebacterium diphtheriae — Do not forcefully strip a suspected diphtheritic membrane
Q168. An immunocompromised patient develops chronic weight loss, cough and haemoptysis, raising concern for tuberculosis. Which organism must be excluded?
Recall paper: January 2025; Microbiology
A. Staphylococcus epidermidis
B. Enterobius vermicularis
C. Mycobacterium tuberculosis
D. Bartonella henselae
Answer and explanation
C. Mycobacterium tuberculosis
Pulmonary tuberculosis is caused by M. tuberculosis and may produce chronic constitutional symptoms, cavitation and haemoptysis. In HIV-associated advanced immunosuppression, imaging may be atypical or disseminated rather than apical.
A. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
B. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
D. Bartonella henselae: Bartonella henselae classically causes regional cat-scratch lymphadenopathy, not this condition.
Exam pearl: Mycobacterium tuberculosis — Steroids plus weight loss and haemoptysis should trigger a TB evaluation.
Q169. Several postoperative ward patients develop C. difficile diarrhoea. What is the typical transmission pathway?
Recall paper: September 2016; Microbiology
A. Faecal–oral spread of environmentally persistent spores via contact
B. Inhalation of airborne toxin
C. Mosquito-borne transmission
D. Haematogenous transmission from other infected patients
Answer and explanation
A. Faecal–oral spread of environmentally persistent spores via contact
C. difficile is mainly transmitted when spores from faeces contaminate hands, equipment or surfaces and are ingested. The disease is toxin mediated within the colon; preformed toxin is not usually passed directly between patients as an airborne agent.
B. Inhalation of airborne toxin: The relevant infection is not mainly spread through inhalation of an airborne agent; the exposure pathway in the question differs.
C. Mosquito-borne transmission: This is a different vector or environmental exposure pathway and is not the transmission mechanism described.
D. Haematogenous transmission from other infected patients: This infection is spread by ingesting spores from the environment, not by sharing blood circulation.
Exam pearl: Faecal–oral spread of environmentally persistent spores via contact — It is C. difficile spores, not airborne toxin, that spread between patients.
Q170. An inpatient develops profuse diarrhoea and colonic pseudomembranes after antimicrobial treatment. Which pathogen is responsible?
Recall paper: September 2016; Microbiology
A. Clostridioides difficile
B. Campylobacter jejuni
C. Shigella dysenteriae
D. Clostridium perfringens
Answer and explanation
A. Clostridioides difficile
Antibiotic disruption of the gut microbiota permits toxin-producing C. difficile proliferation. Toxins A and B produce epithelial injury, inflammation and pseudomembranous colitis.
B. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
C. Shigella dysenteriae: Shigella dysenteriae causes invasive bacillary dysentery and can produce Shiga toxin.
D. Clostridium perfringens: Clostridium perfringens is associated with clostridial myonecrosis, not this organism-specific diagnosis.
Exam pearl: Clostridioides difficile — Do not treat a positive colonisation test without compatible clinical illness.
Q171. Which bacterium is a common cause of infected arterial aneurysm?
Recall paper: January 2017; Microbiology
A. Candida albicans
B. Bordetella pertussis
C. Clostridioides difficile
D. Staphylococcus aureus
Answer and explanation
D. Staphylococcus aureus
S. aureus can cause bloodstream infection and infectious arteritis with aneurysmal degeneration. Salmonella is another classic and important cause of infected aortic aneurysm, especially in vulnerable hosts.
A. Candida albicans: Candida albicans is a yeast causing thrush and opportunistic mucosal or invasive candidiasis, rather than this syndrome.
B. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
C. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Infected aneurysm: remember S. aureus and Salmonella
Q172. Several postoperative ward patients develop C. difficile diarrhoea. What is the typical transmission pathway?
Recall paper: April 2017; Microbiology
A. Inhalation of airborne toxin
B. Faecal–oral spread of environmentally persistent spores via contact
C. Mosquito-borne transmission
D. Haematogenous transmission from other infected patients
Answer and explanation
B. Faecal–oral spread of environmentally persistent spores via contact
C. difficile is mainly transmitted when spores from faeces contaminate hands, equipment or surfaces and are ingested. The disease is toxin mediated within the colon; preformed toxin is not usually passed directly between patients as an airborne agent.
A. Inhalation of airborne toxin: The relevant infection is not mainly spread through inhalation of an airborne agent; the exposure pathway in the question differs.
C. Mosquito-borne transmission: This is a different vector or environmental exposure pathway and is not the transmission mechanism described.
D. Haematogenous transmission from other infected patients: This infection is spread by ingesting spores from the environment, not by sharing blood circulation.
Exam pearl: Faecal–oral spread of environmentally persistent spores via contact — It is C. difficile spores, not airborne toxin, that spread between patients.
Q173. A puncture injury to the fingertip is followed by a tender, tense, fluctuant pulp-space infection. Which pathogen is most likely?
Recall paper: April 2017; Microbiology
A. Staphylococcus aureus
B. Streptococcus pneumoniae
C. Escherichia coli
D. Clostridioides difficile
Answer and explanation
A. Staphylococcus aureus
S. aureus commonly causes a felon, an abscess within the fibrous septa of the digital pulp. Closed compartment pressure can threaten perfusion and necessitate timely drainage.
B. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
C. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Felon = closed-space pulp infection, most often Staphylococcus aureus.
Q174. An intra-abdominal abscess develops following perforated appendicitis. Which microbiological combination is expected?
Recall paper: April 2017; Microbiology
A. Only Staphylococcus epidermidis
B. Only Clostridioides difficile
C. Enteric Gram-negative rods with anaerobes such as Bacteroides fragilis
D. Only Corynebacterium diphtheriae
Answer and explanation
C. Enteric Gram-negative rods with anaerobes such as Bacteroides fragilis
Perforation releases colonic polymicrobial contents into the peritoneum. Escherichia coli and anaerobes, particularly the Bacteroides fragilis group, are important causes of intra-abdominal infection.
A. Only Staphylococcus epidermidis: This device-associated organism is not the universal sole cause of perforated intra-abdominal infection.
B. Only Clostridioides difficile: C. difficile produces colitis after dysbiosis rather than causing typical polymicrobial appendiceal peritonitis.
D. Only Corynebacterium diphtheriae: C. diphtheriae produces respiratory or cutaneous diphtheria, not routine perforated appendiceal abscess.
Exam pearl: Enteric Gram-negative rods with anaerobes such as Bacteroides fragilis — A perforated appendix has mixed enteric flora
Q175. A puncture injury to the fingertip is followed by a tender, tense, fluctuant pulp-space infection. Which pathogen is most likely?
Recall paper: September 2017; Microbiology
A. Streptococcus pneumoniae
B. Escherichia coli
C. Clostridioides difficile
D. Staphylococcus aureus
Answer and explanation
D. Staphylococcus aureus
S. aureus commonly causes a felon, an abscess within the fibrous septa of the digital pulp. Closed compartment pressure can threaten perfusion and necessitate timely drainage.
A. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
B. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
C. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Felon = closed-space pulp infection, most often Staphylococcus aureus.
Q176. A patient with a prosthetic cardiac valve develops indolent infective endocarditis. Which organism has a characteristic prosthetic-surface biofilm association?
Recall paper: September 2017; Microbiology
A. Streptococcus pyogenes
B. Vibrio cholerae
C. Bordetella pertussis
D. Staphylococcus epidermidis
Answer and explanation
D. Staphylococcus epidermidis
Coagulase-negative staphylococci, especially S. epidermidis, adhere to artificial material and form biofilms. This makes prosthetic-device infections more persistent and difficult to eradicate.
A. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
B. Vibrio cholerae: Vibrio cholerae causes profuse watery secretory diarrhoea rather than the syndrome specified.
C. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
Exam pearl: Staphylococcus epidermidis — The most likely organism depends on timing and clinical syndrome
Q177. A child with neonatal meconium ileus and recurrent Pseudomonas pneumonia is investigated for cystic fibrosis. Which sweat measurement is diagnostic?
Recall paper: September 2017; Microbiology
A. Elevated sweat creatinine
B. Elevated sweat chloride
C. Elevated sweat alanine aminotransferase
D. Elevated sweat urea
Answer and explanation
B. Elevated sweat chloride
CFTR dysfunction impairs epithelial chloride transport and produces increased sweat chloride concentration. Chloride testing is interpreted alongside genotype and clinical findings using standardised protocols.
A. Elevated sweat creatinine: Sweat creatinine is not the standard diagnostic abnormality in cystic fibrosis.
C. Elevated sweat alanine aminotransferase: Alanine aminotransferase is a marker of hepatocellular injury, not the characteristic CF sweat test measurement.
D. Elevated sweat urea: Sweat urea is not the diagnostic sweat-electrolyte marker used for cystic fibrosis.
Exam pearl: Elevated sweat chloride — Meconium ileus + recurrent Pseudomonas = cystic fibrosis
Q178. A traumatic wound develops clostridial myonecrosis with gas and rapid tissue destruction. Which organism is classic?
Recall paper: January 2018; Microbiology
A. Clostridium perfringens
B. Clostridioides difficile
C. Staphylococcus epidermidis
D. Neisseria gonorrhoeae
Answer and explanation
A. Clostridium perfringens
C. perfringens is an anaerobic Gram-positive spore-forming rod. Its alpha toxin (phospholipase C) causes muscle injury, haemolysis and severe toxemia in gas gangrene.
B. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
C. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Neisseria gonorrhoeae: Neisseria gonorrhoeae causes sexually transmitted urethritis and sometimes epididymitis or disseminated arthritis.
Exam pearl: Clostridium perfringens — Toxin production explains why clostridial myonecrosis can progress extremely quickly.
Q179. A livestock-associated painless ulcer develops a characteristic black eschar and extensive oedema. Which organism should be suspected?
Recall paper: January 2018; Microbiology
A. Streptococcus pyogenes
B. Staphylococcus aureus
C. Bacillus anthracis
D. Clostridium difficile
Answer and explanation
C. Bacillus anthracis
Cutaneous anthrax may begin as a papule and progress to a painless ulcer with black eschar, sometimes with substantial surrounding oedema. B. anthracis is a spore-forming Gram-positive bacillus.
A. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
B. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
D. Clostridium difficile: Clostridium difficile is the former name of C. difficile, a cause of antibiotic-associated colitis rather than this presentation.
Exam pearl: Bacillus anthracis — Characteristic painless eschar and animal exposure matter more than eschar colour alone.
Q180. A sexually active young man has fever, dysuria, urethral discharge and gradual unilateral epididymal pain. Which organism is a common cause?
Recall paper: January 2018; Microbiology
A. Escherichia coli
B. Staphylococcus epidermidis
C. Chlamydia trachomatis
D. Mumps virus
Answer and explanation
C. Chlamydia trachomatis
C. trachomatis is a frequent cause of epididymitis in younger sexually active men, often with associated urethritis. Gonorrhoea is another important STI cause; testing and empirical treatment should address relevant pathogens.
A. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
B. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Mumps virus: Mumps can cause viral orchitis, usually associated with parotitis, rather than typical sexually transmitted urethritis with discharge.
Exam pearl: Chlamydia trachomatis — Never allow a presumed diagnosis of epididymitis to delay evaluation of possible testicular torsion.
Q181. Several postoperative ward patients develop C. difficile diarrhoea. What is the typical transmission pathway?
Recall paper: April 2018; Microbiology
A. Inhalation of airborne toxin
B. Mosquito-borne transmission
C. Haematogenous transmission from other infected patients
D. Faecal–oral spread of environmentally persistent spores via contact
Answer and explanation
D. Faecal–oral spread of environmentally persistent spores via contact
C. difficile is mainly transmitted when spores from faeces contaminate hands, equipment or surfaces and are ingested. The disease is toxin mediated within the colon; preformed toxin is not usually passed directly between patients as an airborne agent.
A. Inhalation of airborne toxin: The relevant infection is not mainly spread through inhalation of an airborne agent; the exposure pathway in the question differs.
B. Mosquito-borne transmission: This is a different vector or environmental exposure pathway and is not the transmission mechanism described.
C. Haematogenous transmission from other infected patients: This infection is spread by ingesting spores from the environment, not by sharing blood circulation.
Exam pearl: Faecal–oral spread of environmentally persistent spores via contact — It is C. difficile spores, not airborne toxin, that spread between patients.
Q182. A traumatic wound develops clostridial myonecrosis with gas and rapid tissue destruction. Which organism is classic?
Recall paper: April 2018; Microbiology
A. Clostridioides difficile
B. Clostridium perfringens
C. Staphylococcus epidermidis
D. Neisseria gonorrhoeae
Answer and explanation
B. Clostridium perfringens
C. perfringens is an anaerobic Gram-positive spore-forming rod. Its alpha toxin (phospholipase C) causes muscle injury, haemolysis and severe toxemia in gas gangrene.
A. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
C. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Neisseria gonorrhoeae: Neisseria gonorrhoeae causes sexually transmitted urethritis and sometimes epididymitis or disseminated arthritis.
Exam pearl: Clostridium perfringens — Toxin production explains why clostridial myonecrosis can progress extremely quickly.
Q183. A patient has rapidly spreading perineal necrosis and systemic toxicity (Fournier gangrene). What microbiological pattern is classically associated?
Recall paper: September 2018; Microbiology
A. Only Candida albicans
B. Only Streptococcus pneumoniae
C. Polymicrobial aerobic and anaerobic flora
D. Only Mycobacterium tuberculosis
Answer and explanation
C. Polymicrobial aerobic and anaerobic flora
Fournier gangrene is a necrotising fasciitis of the genital and perineal fascial compartments, often caused by a synergy of enteric Gram-negative organisms, streptococci and anaerobes. Monomicrobial infection is possible but not the classic pattern.
A. Only Candida albicans: Candida alone is not the usual explanation for rapidly destructive mixed perineal bacterial infection.
B. Only Streptococcus pneumoniae: Pneumococcus is not the sole cause of necrotising perineal or intra-abdominal infection.
D. Only Mycobacterium tuberculosis: Tuberculosis is generally indolent and is not the classic sole cause of rapid polymicrobial soft-tissue necrosis.
Exam pearl: Polymicrobial aerobic and anaerobic flora — Clinical priority is operative source control, not obtaining a single-organism culture.
Q184. A patient develops fever, abdominal pain and bloody diarrhoea after undercooked poultry. Which pathogen is classically involved?
Recall paper: September 2018; Microbiology
A. Staphylococcus aureus
B. Clostridioides difficile
C. Campylobacter jejuni
D. Bordetella pertussis
Answer and explanation
C. Campylobacter jejuni
Campylobacter jejuni is a curved, motile, Gram-negative organism transmitted especially through contaminated poultry. It causes inflammatory gastroenteritis and can cause ileocolitis resembling an acute surgical abdomen.
A. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
B. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
D. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
Exam pearl: Campylobacter jejuni — Campylobacter is a curved bacillus, not a flagellated diplococcus as one corrupted recall claims.
Q185. Which organism is most commonly associated with haematogenous native pyogenic vertebral osteomyelitis in adults?
Recall paper: January 2019; Microbiology
A. Clostridioides difficile
B. Staphylococcus epidermidis
C. Campylobacter jejuni
D. Staphylococcus aureus
Answer and explanation
D. Staphylococcus aureus
Staphylococcus aureus is the leading cause of adult native vertebral osteomyelitis or pyogenic discitis. Blood cultures, inflammatory markers and MRI help establish the diagnosis and define the extent of infection.
A. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
B. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
C. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
Exam pearl: Staphylococcus aureus — Native pyogenic discitis = S. aureus until proved otherwise
Q186. Which encapsulated bacterium is historically associated with severe childhood epiglottitis?
Recall paper: January 2019; Microbiology
A. Bordetella pertussis
B. Haemophilus influenzae type b
C. Clostridium perfringens
D. Staphylococcus epidermidis
Answer and explanation
B. Haemophilus influenzae type b
Hib historically caused childhood epiglottitis, classically with fever, drooling, dysphagia and stridor. Widespread Hib vaccination has markedly reduced its incidence, and other organisms cause modern cases.
A. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
C. Clostridium perfringens: Clostridium perfringens is associated with clostridial myonecrosis, not this organism-specific diagnosis.
D. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
Exam pearl: Haemophilus influenzae type b — Epiglottitis = airway emergency
Q187. A patient with advanced dental disease develops a deep odontogenic abscess. Which bacterial component is characteristic?
Recall paper: January 2019; Microbiology
A. Anaerobic oral flora including Bacteroides/Prevotella species
B. Salmonella Typhi
C. Neisseria meningitidis
D. Bordetella pertussis
Answer and explanation
A. Anaerobic oral flora including Bacteroides/Prevotella species
Odontogenic infection is generally polymicrobial, with viridans streptococci and anaerobes such as Prevotella, Fusobacterium and related Bacteroides groups. Drainage and removal of the dental source are central.
B. Salmonella Typhi: Salmonella Typhi causes enteric fever, generally a systemic febrile illness rather than the condition in this stem.
C. Neisseria meningitidis: Neisseria meningitidis is a Gram-negative diplococcus causing meningococcal meningitis and sepsis.
D. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
Exam pearl: Anaerobic oral flora including Bacteroides/Prevotella species — Dental abscesses are mixed flora
Q188. Purulent erythema develops around a surgical incision or orthopaedic fixation pin site. Which bacterium is frequently responsible?
Recall paper: January 2019; Microbiology
A. Staphylococcus aureus
B. Streptococcus pneumoniae
C. Enterobius vermicularis
D. Clostridioides difficile
Answer and explanation
A. Staphylococcus aureus
S. aureus is common in purulent superficial surgical-site and skin infections and in infections associated with open fractures or fixation. Deep/organ-space infection may involve different or mixed flora.
B. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
C. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Staph aureus is a common incisional infection organism
Q189. Which organism is most commonly associated with haematogenous native pyogenic vertebral osteomyelitis in adults?
Recall paper: January 2019; Microbiology
A. Clostridioides difficile
B. Staphylococcus aureus
C. Staphylococcus epidermidis
D. Campylobacter jejuni
Answer and explanation
B. Staphylococcus aureus
Staphylococcus aureus is the leading cause of adult native vertebral osteomyelitis or pyogenic discitis. Blood cultures, inflammatory markers and MRI help establish the diagnosis and define the extent of infection.
A. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
C. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
Exam pearl: Staphylococcus aureus — Native pyogenic discitis = S. aureus until proved otherwise
Q190. Purulent erythema develops around a surgical incision or orthopaedic fixation pin site. Which bacterium is frequently responsible?
Recall paper: January 2019; Microbiology
A. Streptococcus pneumoniae
B. Enterobius vermicularis
C. Staphylococcus aureus
D. Clostridioides difficile
Answer and explanation
C. Staphylococcus aureus
S. aureus is common in purulent superficial surgical-site and skin infections and in infections associated with open fractures or fixation. Deep/organ-space infection may involve different or mixed flora.
A. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
B. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Staph aureus is a common incisional infection organism
Q191. Which encapsulated bacterium is historically associated with severe childhood epiglottitis?
Recall paper: January 2019; Microbiology
A. Bordetella pertussis
B. Haemophilus influenzae type b
C. Clostridium perfringens
D. Staphylococcus epidermidis
Answer and explanation
B. Haemophilus influenzae type b
Hib historically caused childhood epiglottitis, classically with fever, drooling, dysphagia and stridor. Widespread Hib vaccination has markedly reduced its incidence, and other organisms cause modern cases.
A. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
C. Clostridium perfringens: Clostridium perfringens is associated with clostridial myonecrosis, not this organism-specific diagnosis.
D. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
Exam pearl: Haemophilus influenzae type b — Epiglottitis = airway emergency
Q192. A patient with advanced dental disease develops a deep odontogenic abscess. Which bacterial component is characteristic?
Recall paper: January 2019; Microbiology
A. Anaerobic oral flora including Bacteroides/Prevotella species
B. Salmonella Typhi
C. Neisseria meningitidis
D. Bordetella pertussis
Answer and explanation
A. Anaerobic oral flora including Bacteroides/Prevotella species
Odontogenic infection is generally polymicrobial, with viridans streptococci and anaerobes such as Prevotella, Fusobacterium and related Bacteroides groups. Drainage and removal of the dental source are central.
B. Salmonella Typhi: Salmonella Typhi causes enteric fever, generally a systemic febrile illness rather than the condition in this stem.
C. Neisseria meningitidis: Neisseria meningitidis is a Gram-negative diplococcus causing meningococcal meningitis and sepsis.
D. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
Exam pearl: Anaerobic oral flora including Bacteroides/Prevotella species — Dental abscesses are mixed flora
Q193. A patient with sickle-cell disease has an acutely inflamed joint suggesting septic arthritis. Which organism is a leading general cause of septic arthritis?
Recall paper: September 2019; Microbiology
A. Salmonella species
B. Staphylococcus aureus
C. Enterobius vermicularis
D. Clostridioides difficile
Answer and explanation
B. Staphylococcus aureus
S. aureus remains a major cause of septic arthritis across patient groups. Although Salmonella is classically associated with osteomyelitis in sickle-cell disease, the same association should not automatically override the usual septic arthritis differential.
A. Salmonella species: Salmonella species are associated with enteric fever, gastroenteritis and a classic sickle-cell osteomyelitis association.
C. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Sickle-cell osteomyelitis and sickle-cell septic arthritis are not identical questions.
Q194. A household develops nocturnal pruritus ani and characteristic eggs on the perianal tape test. Which helminth is implicated?
Recall paper: September 2019; Microbiology
A. Ascaris lumbricoides
B. Trichinella spiralis
C. Enterobius vermicularis
D. Schistosoma haematobium
Answer and explanation
C. Enterobius vermicularis
Enterobius vermicularis is a nematode that deposits ova around the anus at night, provoking itching and household transmission. Diagnosis is commonly made using an early-morning adhesive-tape sample.
A. Ascaris lumbricoides: Ascaris lumbricoides is an intestinal nematode associated with obstruction or biliary migration in heavy infection.
B. Trichinella spiralis: Trichinella spiralis is acquired from infected meat and can cause myalgia, periorbital oedema and eosinophilia.
D. Schistosoma haematobium: Schistosoma haematobium produces urinary schistosomiasis, haematuria and increased squamous bladder-cancer risk.
Exam pearl: Enterobius vermicularis — Pinworm = nighttime perianal itch + adhesive-tape eggs.
Q195. A livestock-associated painless ulcer develops a characteristic black eschar and extensive oedema. Which organism should be suspected?
Recall paper: September 2019; Microbiology
A. Streptococcus pyogenes
B. Bacillus anthracis
C. Staphylococcus aureus
D. Clostridium difficile
Answer and explanation
B. Bacillus anthracis
Cutaneous anthrax may begin as a papule and progress to a painless ulcer with black eschar, sometimes with substantial surrounding oedema. B. anthracis is a spore-forming Gram-positive bacillus.
A. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
C. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
D. Clostridium difficile: Clostridium difficile is the former name of C. difficile, a cause of antibiotic-associated colitis rather than this presentation.
Exam pearl: Bacillus anthracis — Characteristic painless eschar and animal exposure matter more than eschar colour alone.
Q196. Several catheterised inpatients develop healthcare-associated Gram-negative urinary infection. Which opportunistic pathogen is a classic outbreak concern?
Recall paper: January 2020; Microbiology
A. Bordetella pertussis
B. Clostridioides difficile
C. Pseudomonas aeruginosa
D. Streptococcus pneumoniae
Answer and explanation
C. Pseudomonas aeruginosa
Pseudomonas is associated with instrumentation, moist healthcare environments and catheter-associated urinary tract infection. However E. coli and other Enterobacterales remain frequent causes, so cultures and local epidemiology are essential.
A. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
B. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
D. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
Exam pearl: Pseudomonas aeruginosa — Pseudomonas is a classic catheterised-ward organism, not the universal commonest CAUTI pathogen.
Q197. A sexually active young man has fever, dysuria, urethral discharge and gradual unilateral epididymal pain. Which organism is a common cause?
Recall paper: January 2020; Microbiology
A. Escherichia coli
B. Staphylococcus epidermidis
C. Mumps virus
D. Chlamydia trachomatis
Answer and explanation
D. Chlamydia trachomatis
C. trachomatis is a frequent cause of epididymitis in younger sexually active men, often with associated urethritis. Gonorrhoea is another important STI cause; testing and empirical treatment should address relevant pathogens.
A. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
B. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
C. Mumps virus: Mumps can cause viral orchitis, usually associated with parotitis, rather than typical sexually transmitted urethritis with discharge.
Exam pearl: Chlamydia trachomatis — Never allow a presumed diagnosis of epididymitis to delay evaluation of possible testicular torsion.
Q198. A recent traveller develops crampy bloody diarrhoea; investigation supports invasive amoebic colitis. What organism is responsible?
Recall paper: January 2020; Microbiology
A. Campylobacter jejuni
B. Enterobius vermicularis
C. Hepatitis A virus
D. Entamoeba histolytica
Answer and explanation
D. Entamoeba histolytica
Entamoeba histolytica invades colonic mucosa and can cause bloody diarrhoea, flask-shaped ulcers and extraintestinal liver abscess. Specific stool antigen or molecular testing is more discriminatory than cyst microscopy alone.
A. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
B. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
C. Hepatitis A virus: Hepatitis A virus causes faecal–oral acute hepatitis rather than this bacterial or parasitic disease.
Exam pearl: Entamoeba histolytica — Bloody diarrhoea after travel alone is not diagnostic of amoebiasis
Q199. A patient develops indurated cervicofacial swelling and draining sinuses containing sulphur granules after dental disease. Which organism is most likely?
Recall paper: January 2020; Microbiology
A. Actinomyces israelii
B. Nocardia asteroides
C. Histoplasma capsulatum
D. Staphylococcus aureus
Answer and explanation
A. Actinomyces israelii
Actinomyces is a branching, filamentous, Gram-positive anaerobic bacterium that causes chronic invasive actinomycosis. Sulphur granules are bacterial colonies and are particularly characteristic in dental and cervicofacial disease.
B. Nocardia asteroides: Nocardia asteroides is an aerobic branching, weakly acid-fast bacterium more often affecting lungs, CNS or skin.
C. Histoplasma capsulatum: Histoplasma capsulatum is a dimorphic fungus often acquired from contaminated soil or bird/bat-dropping exposure.
D. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
Exam pearl: Actinomyces israelii — Nocardia is typically aerobic and weakly acid-fast
Q200. In a long-term catheterised patient, which pathogen is especially associated with complicated healthcare-acquired urinary infection?
Recall paper: January 2020; Microbiology
A. Pseudomonas aeruginosa
B. Clostridium perfringens
C. Bordetella pertussis
D. Corynebacterium diphtheriae
Answer and explanation
A. Pseudomonas aeruginosa
P. aeruginosa is an important complicated urinary pathogen where devices, resistant organisms and environmental reservoirs are involved. It is not necessarily the most common organism in all catheterised patients.
B. Clostridium perfringens: Clostridium perfringens is associated with clostridial myonecrosis, not this organism-specific diagnosis.
C. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
D. Corynebacterium diphtheriae: Corynebacterium diphtheriae produces pharyngeal pseudomembranes and an exotoxin associated with myocarditis and neuropathy.
Exam pearl: Pseudomonas aeruginosa — Pseudomonas is associated with instrumentation
Q201. A prosthetic hip develops indolent deep infection. Which biofilm-producing organism is classically associated?
Recall paper: January 2020; Microbiology
A. Salmonella Typhi
B. Staphylococcus epidermidis
C. Neisseria meningitidis
D. Vibrio cholerae
Answer and explanation
B. Staphylococcus epidermidis
Coagulase-negative S. epidermidis is an important cause of low-grade prosthetic joint infection because it forms biofilm on implant surfaces. S. aureus is also a major cause and can produce acute aggressive infection.
A. Salmonella Typhi: Salmonella Typhi causes enteric fever, generally a systemic febrile illness rather than the condition in this stem.
C. Neisseria meningitidis: Neisseria meningitidis is a Gram-negative diplococcus causing meningococcal meningitis and sepsis.
D. Vibrio cholerae: Vibrio cholerae causes profuse watery secretory diarrhoea rather than the syndrome specified.
Exam pearl: Staphylococcus epidermidis — Both S. aureus and coagulase-negative staphylococci cause prosthetic joint infection
Q202. After several days of invasive mechanical ventilation, a surgical ICU patient develops new pulmonary infiltrates with fever and purulent secretions. Which pathogen is a recognised cause?
Recall paper: September 2020; Microbiology
A. Pseudomonas aeruginosa
B. Salmonella Typhi
C. Enterobius vermicularis
D. Corynebacterium diphtheriae
Answer and explanation
A. Pseudomonas aeruginosa
Pseudomonas is a major Gram-negative cause of ventilator-associated pneumonia, particularly with prolonged ICU stay, prior antibiotics or resistant hospital flora. Staphylococcus aureus and other Gram-negative bacilli are also important and no single pathogen is universally predominant.
B. Salmonella Typhi: Salmonella Typhi causes enteric fever, generally a systemic febrile illness rather than the condition in this stem.
C. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
D. Corynebacterium diphtheriae: Corynebacterium diphtheriae produces pharyngeal pseudomembranes and an exotoxin associated with myocarditis and neuropathy.
Exam pearl: Pseudomonas aeruginosa — Ventilator-associated pneumonia has multiple likely organisms
Q203. A person with freshwater exposure in an endemic African region develops terminal haematuria. Which parasite is characteristic?
Recall paper: September 2020; Microbiology
A. Schistosoma haematobium
B. Schistosoma mansoni
C. Wuchereria bancrofti
D. Enterobius vermicularis
Answer and explanation
A. Schistosoma haematobium
S. haematobium deposits eggs in the urinary tract, producing haematuria, fibrosis and long-term risk of squamous-cell carcinoma of the bladder. Transmission is through freshwater cercarial penetration.
B. Schistosoma mansoni: Schistosoma mansoni affects mesenteric venules and is associated with intestinal and hepatosplenic disease.
C. Wuchereria bancrofti: Wuchereria bancrofti causes lymphatic filariasis and can produce hydrocele, lymphoedema and chyluria.
D. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
Exam pearl: Schistosoma haematobium — Schistosoma haematobium = haematuria and bladder squamous carcinoma.
Q204. A person with freshwater exposure in an endemic African region develops terminal haematuria. Which parasite is characteristic?
Recall paper: September 2020; Microbiology
A. Schistosoma haematobium
B. Schistosoma mansoni
C. Wuchereria bancrofti
D. Enterobius vermicularis
Answer and explanation
A. Schistosoma haematobium
S. haematobium deposits eggs in the urinary tract, producing haematuria, fibrosis and long-term risk of squamous-cell carcinoma of the bladder. Transmission is through freshwater cercarial penetration.
B. Schistosoma mansoni: Schistosoma mansoni affects mesenteric venules and is associated with intestinal and hepatosplenic disease.
C. Wuchereria bancrofti: Wuchereria bancrofti causes lymphatic filariasis and can produce hydrocele, lymphoedema and chyluria.
D. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
Exam pearl: Schistosoma haematobium — Schistosoma haematobium = haematuria and bladder squamous carcinoma.
Q205. A patient from a lymphatic-filariasis endemic region has a massive hydrocele and chyluria. What is the classic parasite?
Recall paper: September 2020; Microbiology
A. Schistosoma haematobium
B. Wuchereria bancrofti
C. Taenia solium
D. Enterobius vermicularis
Answer and explanation
B. Wuchereria bancrofti
W. bancrofti is a mosquito-borne nematode that inhabits lymphatic vessels. Lymphatic obstruction can produce hydrocele, lymphoedema and leakage of lymph into urine (chyluria).
A. Schistosoma haematobium: Schistosoma haematobium produces urinary schistosomiasis, haematuria and increased squamous bladder-cancer risk.
C. Taenia solium: Taenia solium causes intestinal taeniasis or cysticercosis, not the hallmark syndrome here.
D. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
Exam pearl: Wuchereria bancrofti — Chyluria signifies lymphatic–urinary communication, not simply blood in the urine.
Q206. A person with freshwater exposure in an endemic African region develops terminal haematuria. Which parasite is characteristic?
Recall paper: September 2020; Microbiology
A. Schistosoma haematobium
B. Schistosoma mansoni
C. Wuchereria bancrofti
D. Enterobius vermicularis
Answer and explanation
A. Schistosoma haematobium
S. haematobium deposits eggs in the urinary tract, producing haematuria, fibrosis and long-term risk of squamous-cell carcinoma of the bladder. Transmission is through freshwater cercarial penetration.
B. Schistosoma mansoni: Schistosoma mansoni affects mesenteric venules and is associated with intestinal and hepatosplenic disease.
C. Wuchereria bancrofti: Wuchereria bancrofti causes lymphatic filariasis and can produce hydrocele, lymphoedema and chyluria.
D. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
Exam pearl: Schistosoma haematobium — Schistosoma haematobium = haematuria and bladder squamous carcinoma.
Q207. An ischiorectal abscess contains necrotic surrounding tissue. Which microbiological pattern is characteristic?
Recall paper: September 2020; Microbiology
A. Mixed enteric aerobes and anaerobes
B. Bordetella pertussis alone
C. Mycobacterium leprae alone
D. Rhinovirus alone
Answer and explanation
A. Mixed enteric aerobes and anaerobes
Anorectal abscesses, especially complex or necrotising infections, commonly involve mixed enteric flora including Gram-negative bacilli and anaerobes. Necrotising spread needs urgent debridement and broad antimicrobial cover.
B. Bordetella pertussis alone: A single respiratory pathogen cannot account for an infection that is usually polymicrobial or involves a different tissue.
C. Mycobacterium leprae alone: Leprosy causes slow nerve and cutaneous disease, not acute widespread necrotising sepsis.
D. Rhinovirus alone: Rhinovirus primarily causes upper respiratory illness and is not a typical sole cause of bacterial lobar pneumonia.
Exam pearl: Mixed enteric aerobes and anaerobes — Perineal necrosis suggests polymicrobial anaerobic/aerobic infection and urgent surgery.
Q208. An elderly patient has an MRSA-positive swab from a chronic venous ulcer but no cellulitis, fever or other infection signs. What is the appropriate antibiotic decision?
Recall paper: January 2021; Microbiology
A. No systemic antibiotics for colonisation alone
B. Intravenous vancomycin automatically
C. Oral metronidazole automatically
D. Routine intramuscular gentamicin
Answer and explanation
A. No systemic antibiotics for colonisation alone
A positive superficial swab often represents colonisation rather than clinically relevant tissue infection. In the absence of infection, systemic antibiotics add toxicity and resistance without reliably improving ulcer healing.
B. Intravenous vancomycin automatically: Intravenous vancomycin automatically has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
C. Oral metronidazole automatically: Oral metronidazole automatically has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
D. Routine intramuscular gentamicin: Routine intramuscular gentamicin has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
Exam pearl: No systemic antibiotics for colonisation alone — Culture positivity is not equivalent to infection.
Q209. Several catheterised inpatients develop healthcare-associated Gram-negative urinary infection. Which opportunistic pathogen is a classic outbreak concern?
Recall paper: January 2021; Microbiology
A. Bordetella pertussis
B. Pseudomonas aeruginosa
C. Clostridioides difficile
D. Streptococcus pneumoniae
Answer and explanation
B. Pseudomonas aeruginosa
Pseudomonas is associated with instrumentation, moist healthcare environments and catheter-associated urinary tract infection. However E. coli and other Enterobacterales remain frequent causes, so cultures and local epidemiology are essential.
A. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
C. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
D. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
Exam pearl: Pseudomonas aeruginosa — Pseudomonas is a classic catheterised-ward organism, not the universal commonest CAUTI pathogen.
Q210. A traveller develops an acute hepatitis syndrome after a visit to a region with faecal–oral exposure risk. Which virus is a classic cause?
Recall paper: January 2021; Microbiology
A. Hepatitis A virus
B. Hepatitis C virus
C. Human papillomavirus
D. Human herpesvirus 8
Answer and explanation
A. Hepatitis A virus
HAV spreads by the faecal–oral route and causes acute hepatitis with jaundice, malaise and raised aminotransferases. It does not cause chronic viral hepatitis.
B. Hepatitis C virus: Hepatitis C virus causes blood-borne chronic hepatitis and is not the organism associated with this particular presentation.
C. Human papillomavirus: Human papillomavirus causes epithelial papillomas and is associated with selected anogenital and oropharyngeal carcinomas.
D. Human herpesvirus 8: Human herpesvirus 8 is the Kaposi sarcoma-associated herpesvirus rather than this condition.
Exam pearl: Hepatitis A virus — Clinical HAV typically elevates liver enzymes
Q211. A child with neonatal meconium ileus and recurrent Pseudomonas pneumonia is investigated for cystic fibrosis. Which sweat measurement is diagnostic?
Recall paper: January 2021; Microbiology
A. Elevated sweat creatinine
B. Elevated sweat alanine aminotransferase
C. Elevated sweat urea
D. Elevated sweat chloride
Answer and explanation
D. Elevated sweat chloride
CFTR dysfunction impairs epithelial chloride transport and produces increased sweat chloride concentration. Chloride testing is interpreted alongside genotype and clinical findings using standardised protocols.
A. Elevated sweat creatinine: Sweat creatinine is not the standard diagnostic abnormality in cystic fibrosis.
B. Elevated sweat alanine aminotransferase: Alanine aminotransferase is a marker of hepatocellular injury, not the characteristic CF sweat test measurement.
C. Elevated sweat urea: Sweat urea is not the diagnostic sweat-electrolyte marker used for cystic fibrosis.
Exam pearl: Elevated sweat chloride — Meconium ileus + recurrent Pseudomonas = cystic fibrosis
Q212. An elderly patient has an MRSA-positive swab from a chronic venous ulcer but no cellulitis, fever or other infection signs. What is the appropriate antibiotic decision?
Recall paper: January 2021; Microbiology
A. Intravenous vancomycin automatically
B. No systemic antibiotics for colonisation alone
C. Oral metronidazole automatically
D. Routine intramuscular gentamicin
Answer and explanation
B. No systemic antibiotics for colonisation alone
A positive superficial swab often represents colonisation rather than clinically relevant tissue infection. In the absence of infection, systemic antibiotics add toxicity and resistance without reliably improving ulcer healing.
A. Intravenous vancomycin automatically: Intravenous vancomycin automatically has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
C. Oral metronidazole automatically: Oral metronidazole automatically has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
D. Routine intramuscular gentamicin: Routine intramuscular gentamicin has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
Exam pearl: No systemic antibiotics for colonisation alone — Culture positivity is not equivalent to infection.
Q213. Several catheterised inpatients develop healthcare-associated Gram-negative urinary infection. Which opportunistic pathogen is a classic outbreak concern?
Recall paper: January 2021; Microbiology
A. Pseudomonas aeruginosa
B. Bordetella pertussis
C. Clostridioides difficile
D. Streptococcus pneumoniae
Answer and explanation
A. Pseudomonas aeruginosa
Pseudomonas is associated with instrumentation, moist healthcare environments and catheter-associated urinary tract infection. However E. coli and other Enterobacterales remain frequent causes, so cultures and local epidemiology are essential.
B. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
C. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
D. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
Exam pearl: Pseudomonas aeruginosa — Pseudomonas is a classic catheterised-ward organism, not the universal commonest CAUTI pathogen.
Q214. A child with neonatal meconium ileus and recurrent Pseudomonas pneumonia is investigated for cystic fibrosis. Which sweat measurement is diagnostic?
Recall paper: January 2021; Microbiology
A. Elevated sweat creatinine
B. Elevated sweat alanine aminotransferase
C. Elevated sweat chloride
D. Elevated sweat urea
Answer and explanation
C. Elevated sweat chloride
CFTR dysfunction impairs epithelial chloride transport and produces increased sweat chloride concentration. Chloride testing is interpreted alongside genotype and clinical findings using standardised protocols.
A. Elevated sweat creatinine: Sweat creatinine is not the standard diagnostic abnormality in cystic fibrosis.
B. Elevated sweat alanine aminotransferase: Alanine aminotransferase is a marker of hepatocellular injury, not the characteristic CF sweat test measurement.
D. Elevated sweat urea: Sweat urea is not the diagnostic sweat-electrolyte marker used for cystic fibrosis.
Exam pearl: Elevated sweat chloride — Meconium ileus + recurrent Pseudomonas = cystic fibrosis
Q215. A traveller develops an acute hepatitis syndrome after a visit to a region with faecal–oral exposure risk. Which virus is a classic cause?
Recall paper: January 2021; Microbiology
A. Hepatitis A virus
B. Hepatitis C virus
C. Human papillomavirus
D. Human herpesvirus 8
Answer and explanation
A. Hepatitis A virus
HAV spreads by the faecal–oral route and causes acute hepatitis with jaundice, malaise and raised aminotransferases. It does not cause chronic viral hepatitis.
B. Hepatitis C virus: Hepatitis C virus causes blood-borne chronic hepatitis and is not the organism associated with this particular presentation.
C. Human papillomavirus: Human papillomavirus causes epithelial papillomas and is associated with selected anogenital and oropharyngeal carcinomas.
D. Human herpesvirus 8: Human herpesvirus 8 is the Kaposi sarcoma-associated herpesvirus rather than this condition.
Exam pearl: Hepatitis A virus — Clinical HAV typically elevates liver enzymes
Q216. An individual with chronic limb lymphoedema develops a hot, poorly demarcated, nonpurulent cellulitis. What organism is classically responsible?
Recall paper: January 2021; Microbiology
A. Streptococcus pyogenes
B. Pseudomonas aeruginosa
C. Candida albicans
D. Clostridioides difficile
Answer and explanation
A. Streptococcus pyogenes
Beta-haemolytic streptococci commonly cause spreading nonpurulent cellulitis, and lymphoedema markedly increases recurrence risk. Management includes treatment of infection and attention to skin integrity and underlying oedema.
B. Pseudomonas aeruginosa: Pseudomonas aeruginosa is prominent in burns, catheter-related infection and healthcare-associated pneumonia, not the hallmark being asked.
C. Candida albicans: Candida albicans is a yeast causing thrush and opportunistic mucosal or invasive candidiasis, rather than this syndrome.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Streptococcus pyogenes — Streptococci predominate in typical nonpurulent cellulitis
Q217. An individual with chronic limb lymphoedema develops a hot, poorly demarcated, nonpurulent cellulitis. What organism is classically responsible?
Recall paper: Mixed Jan/Sep 2021; Microbiology
A. Pseudomonas aeruginosa
B. Candida albicans
C. Streptococcus pyogenes
D. Clostridioides difficile
Answer and explanation
C. Streptococcus pyogenes
Beta-haemolytic streptococci commonly cause spreading nonpurulent cellulitis, and lymphoedema markedly increases recurrence risk. Management includes treatment of infection and attention to skin integrity and underlying oedema.
A. Pseudomonas aeruginosa: Pseudomonas aeruginosa is prominent in burns, catheter-related infection and healthcare-associated pneumonia, not the hallmark being asked.
B. Candida albicans: Candida albicans is a yeast causing thrush and opportunistic mucosal or invasive candidiasis, rather than this syndrome.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Streptococcus pyogenes — Streptococci predominate in typical nonpurulent cellulitis
Q218. A patient with recurrent UTIs develops a branching staghorn renal calculus. Which bacterium is classically associated?
Recall paper: Mixed Jan/Sep 2021; Microbiology
A. Escherichia coli
B. Staphylococcus epidermidis
C. Streptococcus pyogenes
D. Proteus mirabilis
Answer and explanation
D. Proteus mirabilis
Proteus mirabilis expresses urease, which splits urea into ammonia, increases urinary pH and promotes magnesium ammonium phosphate (struvite) and carbonate apatite crystallisation. Recurrent urease-producing urinary infection is associated with large branching calculi.
A. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
B. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
C. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
Exam pearl: Proteus mirabilis — Commonest UTI organism is E. coli
Q219. An adult has symptomatic non-fulminant C. difficile infection after clindamycin. What is an accepted targeted oral treatment?
Recall paper: April 2021; Microbiology
A. Intravenous vancomycin alone
B. Routine oral amoxicillin
C. Intravenous gentamicin
D. Oral vancomycin
Answer and explanation
D. Oral vancomycin
Oral vancomycin reaches high intraluminal colonic concentrations and is effective for C. difficile colitis. Current guidelines favour fidaxomicin where feasible, but oral vancomycin remains an accepted alternative.
A. Intravenous vancomycin alone: Intravenous vancomycin alone has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
B. Routine oral amoxicillin: Oral amoxicillin has restricted coverage for some Gram-negative or beta-lactamase-producing pathogens and may not fit this syndrome.
C. Intravenous gentamicin: Intravenous gentamicin has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
Exam pearl: Oral vancomycin — IV vancomycin alone does not adequately treat colonic C. difficile infection.
Q220. An intravenous drug user develops a hot swollen joint with Gram-positive cocci on aspirate. What organism is a leading cause?
Recall paper: April 2021; Microbiology
A. Staphylococcus aureus
B. Campylobacter jejuni
C. Candida albicans
D. Clostridioides difficile
Answer and explanation
A. Staphylococcus aureus
S. aureus is the leading cause of native-joint septic arthritis in most adult populations and is strongly associated with bacteraemia. Joint aspiration and early drainage/antimicrobial therapy are important.
B. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
C. Candida albicans: Candida albicans is a yeast causing thrush and opportunistic mucosal or invasive candidiasis, rather than this syndrome.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Staph aureus remains the principal septic arthritis organism even in high-risk hosts.
Q221. In a patient on clindamycin who develops confirmed C. difficile colitis, which modern oral agent is an accepted targeted alternative to fidaxomicin?
Recall paper: April 2021; Microbiology
A. Oral amoxicillin
B. Intravenous ceftriaxone alone
C. Oral erythromycin
D. Oral vancomycin
Answer and explanation
D. Oral vancomycin
Oral vancomycin is an accepted treatment for symptomatic C. difficile infection and is preferred over historical metronidazole-only strategies when fidaxomicin is not used. The original recall offers metronidazole but not oral vancomycin, illustrating guideline drift.
A. Oral amoxicillin: Amoxicillin lacks reliable activity against many beta-lactamase-producing complicated-infection isolates and may be inadequate here.
B. Intravenous ceftriaxone alone: Intravenous ceftriaxone alone has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
C. Oral erythromycin: Oral erythromycin has a different antimicrobial spectrum, route or clinical role; the defined syndrome calls for a specifically indicated or culture-directed approach.
Exam pearl: Oral vancomycin — A historical source answer can be outdated even if correctly recalled.
Q222. Why do inflamed wound edges become swollen and oedematous during acute inflammation?
Recall paper: April 2021; Pathology
A. Reduced capillary blood flow with no leakage
B. Failure of all neutrophil migration
C. Increased vascular permeability with exudation
D. Complete occlusion of lymphatic channels in every case
Answer and explanation
C. Increased vascular permeability with exudation
Mediators such as histamine and inflammatory cytokines enhance microvascular permeability, allowing protein-rich exudate to move into interstitial tissue. Vasodilation contributes erythema and warmth.
A. Reduced capillary blood flow with no leakage: This omits necessary evaluation or infection control and does not address the clinical risk described.
B. Failure of all neutrophil migration: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
D. Complete occlusion of lymphatic channels in every case: Inflammatory swelling can arise from increased microvascular leakage without complete mechanical lymphatic obstruction.
Exam pearl: Increased vascular permeability with exudation — Permeability explains oedema
Q223. A puncture injury to the fingertip is followed by a tender, tense, fluctuant pulp-space infection. Which pathogen is most likely?
Recall paper: April 2021; Microbiology
A. Streptococcus pneumoniae
B. Escherichia coli
C. Staphylococcus aureus
D. Clostridioides difficile
Answer and explanation
C. Staphylococcus aureus
S. aureus commonly causes a felon, an abscess within the fibrous septa of the digital pulp. Closed compartment pressure can threaten perfusion and necessitate timely drainage.
A. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
B. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Felon = closed-space pulp infection, most often Staphylococcus aureus.
Q224. An intravenous drug user develops a hot swollen joint with Gram-positive cocci on aspirate. What organism is a leading cause?
Recall paper: April 2021; Microbiology
A. Campylobacter jejuni
B. Candida albicans
C. Staphylococcus aureus
D. Clostridioides difficile
Answer and explanation
C. Staphylococcus aureus
S. aureus is the leading cause of native-joint septic arthritis in most adult populations and is strongly associated with bacteraemia. Joint aspiration and early drainage/antimicrobial therapy are important.
A. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
B. Candida albicans: Candida albicans is a yeast causing thrush and opportunistic mucosal or invasive candidiasis, rather than this syndrome.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Staph aureus remains the principal septic arthritis organism even in high-risk hosts.
Q225. A patient taking steroids and azathioprine develops painful swallowing and dysphagia after antibiotics. Which opportunistic infection is likely?
Recall paper: April 2021; Microbiology
A. Pneumocystis jirovecii
B. Candida albicans
C. Toxoplasma gondii
D. Clostridioides difficile
Answer and explanation
B. Candida albicans
Immunosuppression and antibacterial exposure predispose to oral and oesophageal candidiasis, which can cause dysphagia and odynophagia. Other causes, particularly CMV or HSV, remain possible depending on immune status and findings.
A. Pneumocystis jirovecii: Pneumocystis jirovecii is an opportunistic fungal cause of subacute diffuse pneumonia, especially with impaired cellular immunity.
C. Toxoplasma gondii: Toxoplasma causes opportunistic cerebral disease or systemic protozoal infection rather than Candida-type oesophagitis.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Candida albicans — Steroids + antibiotics + odynophagia = consider Candida oesophagitis.
Q226. A traumatic wound develops clostridial myonecrosis with gas and rapid tissue destruction. Which organism is classic?
Recall paper: September 2021; Microbiology
A. Clostridioides difficile
B. Clostridium perfringens
C. Staphylococcus epidermidis
D. Neisseria gonorrhoeae
Answer and explanation
B. Clostridium perfringens
C. perfringens is an anaerobic Gram-positive spore-forming rod. Its alpha toxin (phospholipase C) causes muscle injury, haemolysis and severe toxemia in gas gangrene.
A. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
C. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Neisseria gonorrhoeae: Neisseria gonorrhoeae causes sexually transmitted urethritis and sometimes epididymitis or disseminated arthritis.
Exam pearl: Clostridium perfringens — Toxin production explains why clostridial myonecrosis can progress extremely quickly.
Q227. An adult with sickle-cell disease develops lobar bacterial pneumonia. Which encapsulated organism is an important classic cause?
Recall paper: September 2021; Microbiology
A. Streptococcus pneumoniae
B. Pneumocystis jirovecii
C. Aspergillus fumigatus
D. Respiratory syncytial virus
Answer and explanation
A. Streptococcus pneumoniae
Patients with sickle-cell disease may develop functional asplenia, increasing susceptibility to invasive infection with encapsulated organisms such as S. pneumoniae. Pneumonia must also be assessed for acute chest syndrome.
B. Pneumocystis jirovecii: Pneumocystis jirovecii is an opportunistic fungal cause of subacute diffuse pneumonia, especially with impaired cellular immunity.
C. Aspergillus fumigatus: Aspergillus fumigatus is an opportunistic mould associated with pulmonary aspergillosis rather than the tested bacterial cause.
D. Respiratory syncytial virus: The relevant infection is not mainly spread through inhalation of an airborne agent; the exposure pathway in the question differs.
Exam pearl: Streptococcus pneumoniae — Sickle cell + lobar pneumonia = think pneumococcus and acute chest syndrome.
Q228. A patient develops indurated cervicofacial swelling and draining sinuses containing sulphur granules after dental disease. Which organism is most likely?
Recall paper: May 2022; Microbiology
A. Nocardia asteroides
B. Histoplasma capsulatum
C. Actinomyces israelii
D. Staphylococcus aureus
Answer and explanation
C. Actinomyces israelii
Actinomyces is a branching, filamentous, Gram-positive anaerobic bacterium that causes chronic invasive actinomycosis. Sulphur granules are bacterial colonies and are particularly characteristic in dental and cervicofacial disease.
A. Nocardia asteroides: Nocardia asteroides is an aerobic branching, weakly acid-fast bacterium more often affecting lungs, CNS or skin.
B. Histoplasma capsulatum: Histoplasma capsulatum is a dimorphic fungus often acquired from contaminated soil or bird/bat-dropping exposure.
D. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
Exam pearl: Actinomyces israelii — Nocardia is typically aerobic and weakly acid-fast
Q229. A solid-organ transplant recipient in the intermediate post-transplant period develops unexplained pneumonitis and systemic symptoms. What opportunistic virus should be investigated?
Recall paper: May 2022; Microbiology
A. Epstein–Barr virus
B. Human papillomavirus
C. Hepatitis A virus
D. Cytomegalovirus
Answer and explanation
D. Cytomegalovirus
CMV can produce a viral syndrome and tissue-invasive disease including pneumonitis after transplantation. Risk is affected by donor/recipient serostatus, prophylaxis, immunosuppression and time since transplant.
A. Epstein–Barr virus: Epstein–Barr virus causes infectious mononucleosis and is linked to several lymphomas and nasopharyngeal carcinoma.
B. Human papillomavirus: Human papillomavirus causes epithelial papillomas and is associated with selected anogenital and oropharyngeal carcinomas.
C. Hepatitis A virus: Hepatitis A virus causes faecal–oral acute hepatitis rather than this bacterial or parasitic disease.
Exam pearl: Cytomegalovirus — A transplant patient’s pneumonia cannot be diagnosed as CMV from transplant status alone
Q230. A puncture injury to the fingertip is followed by a tender, tense, fluctuant pulp-space infection. Which pathogen is most likely?
Recall paper: May 2022; Microbiology
A. Streptococcus pneumoniae
B. Escherichia coli
C. Staphylococcus aureus
D. Clostridioides difficile
Answer and explanation
C. Staphylococcus aureus
S. aureus commonly causes a felon, an abscess within the fibrous septa of the digital pulp. Closed compartment pressure can threaten perfusion and necessitate timely drainage.
A. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
B. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Felon = closed-space pulp infection, most often Staphylococcus aureus.
Q231. A patient develops indurated cervicofacial swelling and draining sinuses containing sulphur granules after dental disease. Which organism is most likely?
Recall paper: September 2022; Microbiology
A. Nocardia asteroides
B. Actinomyces israelii
C. Histoplasma capsulatum
D. Staphylococcus aureus
Answer and explanation
B. Actinomyces israelii
Actinomyces is a branching, filamentous, Gram-positive anaerobic bacterium that causes chronic invasive actinomycosis. Sulphur granules are bacterial colonies and are particularly characteristic in dental and cervicofacial disease.
A. Nocardia asteroides: Nocardia asteroides is an aerobic branching, weakly acid-fast bacterium more often affecting lungs, CNS or skin.
C. Histoplasma capsulatum: Histoplasma capsulatum is a dimorphic fungus often acquired from contaminated soil or bird/bat-dropping exposure.
D. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
Exam pearl: Actinomyces israelii — Nocardia is typically aerobic and weakly acid-fast
Q232. An inpatient develops profuse diarrhoea and colonic pseudomembranes after antimicrobial treatment. Which pathogen is responsible?
Recall paper: September 2022; Microbiology
A. Clostridioides difficile
B. Campylobacter jejuni
C. Shigella dysenteriae
D. Clostridium perfringens
Answer and explanation
A. Clostridioides difficile
Antibiotic disruption of the gut microbiota permits toxin-producing C. difficile proliferation. Toxins A and B produce epithelial injury, inflammation and pseudomembranous colitis.
B. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
C. Shigella dysenteriae: Shigella dysenteriae causes invasive bacillary dysentery and can produce Shiga toxin.
D. Clostridium perfringens: Clostridium perfringens is associated with clostridial myonecrosis, not this organism-specific diagnosis.
Exam pearl: Clostridioides difficile — Do not treat a positive colonisation test without compatible clinical illness.
Q233. A household develops nocturnal pruritus ani and characteristic eggs on the perianal tape test. Which helminth is implicated?
Recall paper: Paper/session not recorded in source; Microbiology
A. Ascaris lumbricoides
B. Trichinella spiralis
C. Enterobius vermicularis
D. Schistosoma haematobium
Answer and explanation
C. Enterobius vermicularis
Enterobius vermicularis is a nematode that deposits ova around the anus at night, provoking itching and household transmission. Diagnosis is commonly made using an early-morning adhesive-tape sample.
A. Ascaris lumbricoides: Ascaris lumbricoides is an intestinal nematode associated with obstruction or biliary migration in heavy infection.
B. Trichinella spiralis: Trichinella spiralis is acquired from infected meat and can cause myalgia, periorbital oedema and eosinophilia.
D. Schistosoma haematobium: Schistosoma haematobium produces urinary schistosomiasis, haematuria and increased squamous bladder-cancer risk.
Exam pearl: Enterobius vermicularis — Pinworm = nighttime perianal itch + adhesive-tape eggs.
Q234. Several people develop vomiting two hours after a shared meal. Which pathogen causes classically rapid food poisoning through preformed toxin?
Recall paper: Paper/session not recorded in source; Microbiology
A. Campylobacter jejuni
B. Staphylococcus aureus
C. Salmonella Typhi
D. Clostridioides difficile
Answer and explanation
B. Staphylococcus aureus
Staphylococcal enterotoxin formed in contaminated food can produce abrupt vomiting within about 1–6 hours of ingestion. Illness is usually self-limited and is treated with supportive fluids.
A. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
C. Salmonella Typhi: Salmonella Typhi causes enteric fever, generally a systemic febrile illness rather than the condition in this stem.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Vomiting within hours suggests preformed toxin.
Q235. How does Clostridium perfringens usually appear on Gram staining?
Recall paper: Paper/session not recorded in source; Microbiology
A. Gram-negative diplococci
B. Gram-positive rods
C. Gram-positive cocci in clusters
D. Gram-negative curved bacilli
Answer and explanation
B. Gram-positive rods
C. perfringens is a large anaerobic Gram-positive bacillus capable of toxin-mediated soft-tissue infection. Sporulation may be difficult to demonstrate in tissue specimens.
A. Gram-negative diplococci: This staining and morphology pattern fits organisms such as Neisseria, rather than Gram-positive Clostridium rods.
C. Gram-positive cocci in clusters: Cocci in clusters suggest staphylococci, whereas the organism discussed is rod-shaped.
D. Gram-negative curved bacilli: Curved Gram-negative rods suggest Vibrio or Campylobacter, not this Gram-positive anaerobe.
Exam pearl: Gram-positive rods — Clostridium perfringens = anaerobic Gram-positive rod.
Q236. A patient develops a deep intra-abdominal infection following perforated appendicitis. Which flora are typically implicated?
Recall paper: Paper/session not recorded in source; Microbiology
A. Enteric Gram-negative organisms and anaerobes
B. Streptococcus pneumoniae alone
C. Bordetella pertussis alone
D. Staphylococcus epidermidis alone
Answer and explanation
A. Enteric Gram-negative organisms and anaerobes
Perforation releases bowel organisms including E. coli and anaerobic species such as Bacteroides fragilis group. Superficial incisional infection may be due to skin flora, but deep organ-space infection is commonly polymicrobial.
B. Streptococcus pneumoniae alone: Pneumococcus can cause invasive infection but cannot alone account for the usual mixed flora of this deep abscess.
C. Bordetella pertussis alone: A single respiratory pathogen cannot account for an infection that is usually polymicrobial or involves a different tissue.
D. Staphylococcus epidermidis alone: Coagulase-negative staphylococci can infect devices, but this clinical syndrome cannot be assumed to arise from that organism alone.
Exam pearl: Enteric Gram-negative organisms and anaerobes — Distinguish superficial incisional SSI from an intra-abdominal abscess after appendicectomy.
Q237. A household develops nocturnal pruritus ani and characteristic eggs on the perianal tape test. Which helminth is implicated?
Recall paper: January 2023; Microbiology
A. Ascaris lumbricoides
B. Enterobius vermicularis
C. Trichinella spiralis
D. Schistosoma haematobium
Answer and explanation
B. Enterobius vermicularis
Enterobius vermicularis is a nematode that deposits ova around the anus at night, provoking itching and household transmission. Diagnosis is commonly made using an early-morning adhesive-tape sample.
A. Ascaris lumbricoides: Ascaris lumbricoides is an intestinal nematode associated with obstruction or biliary migration in heavy infection.
C. Trichinella spiralis: Trichinella spiralis is acquired from infected meat and can cause myalgia, periorbital oedema and eosinophilia.
D. Schistosoma haematobium: Schistosoma haematobium produces urinary schistosomiasis, haematuria and increased squamous bladder-cancer risk.
Exam pearl: Enterobius vermicularis — Pinworm = nighttime perianal itch + adhesive-tape eggs.
Q238. Tender ascending red streaks develop from a recent skin puncture. What is the classic pathogen?
Recall paper: January 2023; Microbiology
A. Staphylococcus epidermidis
B. Streptococcus pyogenes
C. Escherichia coli
D. Sporothrix schenckii
Answer and explanation
B. Streptococcus pyogenes
Group A beta-haemolytic streptococci commonly cause rapidly advancing nonpurulent cellulitis and lymphangitis. The tender proximal erythematous streaks reflect inflammation of superficial lymphatic vessels.
A. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
C. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
D. Sporothrix schenckii: Sporothrix causes delayed nodular lymphangitis following plant inoculation, rather than an acute red streak within 24–48 hours.
Exam pearl: Streptococcus pyogenes — Plant-thorn history alone does not prove sporotrichosis
Q239. An organ transplant recipient develops pneumonia despite antibacterial therapy. Which statement best guides the infectious differential?
Recall paper: May 2023; Microbiology
A. Cytomegalovirus is necessarily the cause at every transplant time point
B. The transplant organ does not affect risk
C. Timing after transplantation and immunosuppressive status help distinguish bacterial, viral and fungal infections
D. Negative response to antibiotics proves a viral diagnosis
Answer and explanation
C. Timing after transplantation and immunosuppressive status help distinguish bacterial, viral and fungal infections
CMV pneumonitis is an important transplant infection, especially after the first month or when prophylaxis is stopped; early postoperative infections are often bacterial or donor/recipient derived. The original recall variants have discordant or missing postoperative timelines and cannot establish one pathogen from antibiotic nonresponse alone.
A. Cytomegalovirus is necessarily the cause at every transplant time point: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
B. The transplant organ does not affect risk: Heart, lung, kidney and other solid-organ transplants have different infection risks and immunosuppression regimens.
D. Negative response to antibiotics proves a viral diagnosis: Poor antibacterial response may reflect resistant bacteria, inadequate source control, fungal disease or a noninfectious diagnosis.
Exam pearl: Timing after transplantation and immunosuppressive status help distinguish bacterial, viral and fungal infections — Transplant pneumonia is time-dependent
Q240. A child with neonatal meconium ileus and recurrent Pseudomonas pneumonia is investigated for cystic fibrosis. Which sweat measurement is diagnostic?
Recall paper: May 2023; Microbiology
A. Elevated sweat chloride
B. Elevated sweat creatinine
C. Elevated sweat alanine aminotransferase
D. Elevated sweat urea
Answer and explanation
A. Elevated sweat chloride
CFTR dysfunction impairs epithelial chloride transport and produces increased sweat chloride concentration. Chloride testing is interpreted alongside genotype and clinical findings using standardised protocols.
B. Elevated sweat creatinine: Sweat creatinine is not the standard diagnostic abnormality in cystic fibrosis.
C. Elevated sweat alanine aminotransferase: Alanine aminotransferase is a marker of hepatocellular injury, not the characteristic CF sweat test measurement.
D. Elevated sweat urea: Sweat urea is not the diagnostic sweat-electrolyte marker used for cystic fibrosis.
Exam pearl: Elevated sweat chloride — Meconium ileus + recurrent Pseudomonas = cystic fibrosis
Q241. A child has febrile right iliac fossa pain and mesenteric adenitis after exposure to pigs, with a normal appendix. Which organism is characteristic?
Recall paper: January 2024; Microbiology
A. Staphylococcus aureus
B. Clostridioides difficile
C. Bordetella pertussis
D. Yersinia enterocolitica
Answer and explanation
D. Yersinia enterocolitica
Y. enterocolitica may cause ileitis and mesenteric adenitis, presenting as pseudoappendicitis. Exposure to pigs and contaminated pork is an important epidemiological clue.
A. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
B. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
C. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
Exam pearl: Yersinia enterocolitica — Pig exposure + mesenteric adenitis + normal appendix = Yersinia.
Q242. A patient develops fever and diarrhoea after consuming contaminated eggs or poultry. Which bacterium is classically associated?
Recall paper: January 2024; Microbiology
A. Campylobacter jejuni
B. Clostridioides difficile
C. Staphylococcus epidermidis
D. Nontyphoidal Salmonella
Answer and explanation
D. Nontyphoidal Salmonella
Nontyphoidal Salmonella is a classic foodborne pathogen associated with eggs, poultry and inadequately cooked meat. Incubation commonly ranges from hours to days and may include fever, abdominal cramping and diarrhoea.
A. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
B. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
C. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
Exam pearl: Nontyphoidal Salmonella — Source says “flagellated diplococci”, which is morphologically inconsistent with both Salmonella and Campylobacter
Q243. A diabetic patient has gallbladder wall gas on imaging with acute cholecystitis. What pathogen is a classic gas-producing cause?
Recall paper: January 2024; Microbiology
A. Campylobacter jejuni
B. Streptococcus pneumoniae
C. Clostridium perfringens
D. Enterobius vermicularis
Answer and explanation
C. Clostridium perfringens
Emphysematous cholecystitis is associated with gas-forming infection, including clostridia and Enterobacterales such as E. coli and Klebsiella. Clostridium perfringens is a classic possible organism, but no single pathogen is obligatory.
A. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
B. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
D. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
Exam pearl: Clostridium perfringens — Emphysematous cholecystitis is often polymicrobial
Q244. A household develops nocturnal pruritus ani and characteristic eggs on the perianal tape test. Which helminth is implicated?
Recall paper: September 2024; Microbiology
A. Ascaris lumbricoides
B. Trichinella spiralis
C. Schistosoma haematobium
D. Enterobius vermicularis
Answer and explanation
D. Enterobius vermicularis
Enterobius vermicularis is a nematode that deposits ova around the anus at night, provoking itching and household transmission. Diagnosis is commonly made using an early-morning adhesive-tape sample.
A. Ascaris lumbricoides: Ascaris lumbricoides is an intestinal nematode associated with obstruction or biliary migration in heavy infection.
B. Trichinella spiralis: Trichinella spiralis is acquired from infected meat and can cause myalgia, periorbital oedema and eosinophilia.
C. Schistosoma haematobium: Schistosoma haematobium produces urinary schistosomiasis, haematuria and increased squamous bladder-cancer risk.
Exam pearl: Enterobius vermicularis — Pinworm = nighttime perianal itch + adhesive-tape eggs.
Q245. Which organism is most commonly associated with haematogenous native pyogenic vertebral osteomyelitis in adults?
Recall paper: September 2024; Microbiology
A. Clostridioides difficile
B. Staphylococcus aureus
C. Staphylococcus epidermidis
D. Campylobacter jejuni
Answer and explanation
B. Staphylococcus aureus
Staphylococcus aureus is the leading cause of adult native vertebral osteomyelitis or pyogenic discitis. Blood cultures, inflammatory markers and MRI help establish the diagnosis and define the extent of infection.
A. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
C. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
Exam pearl: Staphylococcus aureus — Native pyogenic discitis = S. aureus until proved otherwise
Q246. A child has neutrophilic meningitis and Gram-positive diplococci in CSF. Which organism is likely?
Recall paper: September 2024; Microbiology
A. Neisseria meningitidis
B. Haemophilus influenzae
C. Escherichia coli
D. Streptococcus pneumoniae
Answer and explanation
D. Streptococcus pneumoniae
S. pneumoniae is an encapsulated Gram-positive lancet-shaped diplococcus that causes invasive bacterial meningitis. Neisseria meningitidis is also a diplococcus but Gram-negative.
A. Neisseria meningitidis: Neisseria meningitidis is a Gram-negative diplococcus causing meningococcal meningitis and sepsis.
B. Haemophilus influenzae: Haemophilus influenzae is a Gram-negative coccobacillus associated with respiratory infection and historically Hib epiglottitis.
C. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
Exam pearl: Streptococcus pneumoniae — Gram-positive diplococci in meningitis = pneumococcus.
Q247. A child has febrile right iliac fossa pain and mesenteric adenitis after exposure to pigs, with a normal appendix. Which organism is characteristic?
Recall paper: April 2025; Microbiology
A. Staphylococcus aureus
B. Clostridioides difficile
C. Bordetella pertussis
D. Yersinia enterocolitica
Answer and explanation
D. Yersinia enterocolitica
Y. enterocolitica may cause ileitis and mesenteric adenitis, presenting as pseudoappendicitis. Exposure to pigs and contaminated pork is an important epidemiological clue.
A. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
B. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
C. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
Exam pearl: Yersinia enterocolitica — Pig exposure + mesenteric adenitis + normal appendix = Yersinia.
Q248. Which organism is most commonly associated with haematogenous native pyogenic vertebral osteomyelitis in adults?
Recall paper: April 2025; Microbiology
A. Clostridioides difficile
B. Staphylococcus epidermidis
C. Campylobacter jejuni
D. Staphylococcus aureus
Answer and explanation
D. Staphylococcus aureus
Staphylococcus aureus is the leading cause of adult native vertebral osteomyelitis or pyogenic discitis. Blood cultures, inflammatory markers and MRI help establish the diagnosis and define the extent of infection.
A. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
B. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
C. Campylobacter jejuni: Campylobacter jejuni is a common poultry-associated cause of inflammatory diarrhoea, usually after a longer incubation than preformed toxin syndromes.
Exam pearl: Staphylococcus aureus — Native pyogenic discitis = S. aureus until proved otherwise
Q249. A breastfeeding woman develops tender erythema and a fluctuant breast collection. What organism is a frequent cause?
Recall paper: Paper/session not recorded in source; Microbiology
A. Streptococcus pneumoniae
B. Enterococcus faecalis
C. Staphylococcus aureus
D. Clostridium difficile
Answer and explanation
C. Staphylococcus aureus
S. aureus is a common cause of lactational mastitis and associated breast abscess. Ultrasound is useful when an abscess is suspected, with drainage and appropriate antibiotics according to clinical assessment.
A. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
B. Enterococcus faecalis: Enterococcus faecalis may cause urinary or endovascular infection but is not the most characteristic answer here.
D. Clostridium difficile: Clostridium difficile is the former name of C. difficile, a cause of antibiotic-associated colitis rather than this presentation.
Exam pearl: Staphylococcus aureus — Lactational abscess = frequently S. aureus
Q250. A patient develops indurated cervicofacial swelling and draining sinuses containing sulphur granules after dental disease. Which organism is most likely?
Recall paper: Paper/session not recorded in source; Microbiology
A. Nocardia asteroides
B. Actinomyces israelii
C. Histoplasma capsulatum
D. Staphylococcus aureus
Answer and explanation
B. Actinomyces israelii
Actinomyces is a branching, filamentous, Gram-positive anaerobic bacterium that causes chronic invasive actinomycosis. Sulphur granules are bacterial colonies and are particularly characteristic in dental and cervicofacial disease.
A. Nocardia asteroides: Nocardia asteroides is an aerobic branching, weakly acid-fast bacterium more often affecting lungs, CNS or skin.
C. Histoplasma capsulatum: Histoplasma capsulatum is a dimorphic fungus often acquired from contaminated soil or bird/bat-dropping exposure.
D. Staphylococcus aureus: Staphylococcus aureus commonly causes purulent skin infection, abscess, bacteraemia and pyogenic osteomyelitis, but not the specific process tested.
Exam pearl: Actinomyces israelii — Nocardia is typically aerobic and weakly acid-fast
Q251. Purulent erythema develops around a surgical incision or orthopaedic fixation pin site. Which bacterium is frequently responsible?
Recall paper: Paper/session not recorded in source; Microbiology
A. Staphylococcus aureus
B. Streptococcus pneumoniae
C. Enterobius vermicularis
D. Clostridioides difficile
Answer and explanation
A. Staphylococcus aureus
S. aureus is common in purulent superficial surgical-site and skin infections and in infections associated with open fractures or fixation. Deep/organ-space infection may involve different or mixed flora.
B. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
C. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Staph aureus is a common incisional infection organism
Q252. A burn wound develops characteristic opportunistic infection in a prolonged hospital stay. What organism is classically associated?
Recall paper: January 2026; Microbiology
A. Bordetella pertussis
B. Enterobius vermicularis
C. Pseudomonas aeruginosa
D. Clostridioides difficile
Answer and explanation
C. Pseudomonas aeruginosa
P. aeruginosa colonises moist environments and can infect burns or other compromised tissues, sometimes producing blue-green pigment. It is one of several organisms involved in burn wound infection.
A. Bordetella pertussis: Bordetella pertussis causes whooping cough, not the typical infectious process described.
B. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Pseudomonas aeruginosa — Pseudomonas is a classic burn wound pathogen, but it is not exclusive.
Q253. Recurrent infection has failed to improve with empiric antibiotics; the source does not specify site, cultures, dose or immune status. Which approach is most appropriate?
Recall paper: January 2025; Microbiology
A. Assume all failures are fungal infections
B. Escalate antibiotics without evaluating drainage or resistance
C. Reassess diagnosis, source control, microbiology and antimicrobial exposure
D. Attribute all failures to steroid exposure
Answer and explanation
C. Reassess diagnosis, source control, microbiology and antimicrobial exposure
Treatment failure has multiple causes: inaccurate diagnosis, inadequate drainage, resistant organisms, subtherapeutic dosing, poor penetration, poor adherence or host factors. The original abbreviated source cannot identify a single cause.
A. Assume all failures are fungal infections: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
B. Escalate antibiotics without evaluating drainage or resistance: This omits necessary evaluation or infection control and does not address the clinical risk described.
D. Attribute all failures to steroid exposure: The conclusion is too absolute for the clinical evidence provided; distinguishing clinical findings and investigations are required.
Exam pearl: Reassess diagnosis, source control, microbiology and antimicrobial exposure — Infection failing antibiotics is not necessarily antibiotic failure
Q254. Purulent erythema develops around a surgical incision or orthopaedic fixation pin site. Which bacterium is frequently responsible?
Recall paper: May 2024; Microbiology
A. Streptococcus pneumoniae
B. Staphylococcus aureus
C. Enterobius vermicularis
D. Clostridioides difficile
Answer and explanation
B. Staphylococcus aureus
S. aureus is common in purulent superficial surgical-site and skin infections and in infections associated with open fractures or fixation. Deep/organ-space infection may involve different or mixed flora.
A. Streptococcus pneumoniae: Streptococcus pneumoniae is an encapsulated Gram-positive diplococcus associated with pneumonia, meningitis and invasive asplenic infection.
C. Enterobius vermicularis: Enterobius vermicularis causes nocturnal perianal pruritus and is diagnosed with adhesive-tape sampling.
D. Clostridioides difficile: Clostridioides difficile produces toxin-mediated antibiotic-associated colitis rather than the syndrome specified.
Exam pearl: Staphylococcus aureus — Staph aureus is a common incisional infection organism
Q255. Which organism is the leading cause of uncomplicated community-acquired urinary tract infection?
Recall paper: January 2025; Microbiology
A. Escherichia coli
B. Proteus mirabilis
C. Pseudomonas aeruginosa
D. Staphylococcus epidermidis
Answer and explanation
A. Escherichia coli
Uropathogenic E. coli causes the majority of uncomplicated community-acquired UTIs because it adheres to uroepithelium using fimbrial adhesins and can ascend from periurethral flora.
B. Proteus mirabilis: Proteus mirabilis is urease-positive and particularly associated with infection stones, not every ordinary urinary infection.
C. Pseudomonas aeruginosa: Pseudomonas aeruginosa is prominent in burns, catheter-related infection and healthcare-associated pneumonia, not the hallmark being asked.
D. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
Exam pearl: Escherichia coli — Overall UTI leader: E. coli
Q256. A patient with recurrent UTIs develops a branching staghorn renal calculus. Which bacterium is classically associated?
Recall paper: May 2024; Microbiology
A. Escherichia coli
B. Staphylococcus epidermidis
C. Proteus mirabilis
D. Streptococcus pyogenes
Answer and explanation
C. Proteus mirabilis
Proteus mirabilis expresses urease, which splits urea into ammonia, increases urinary pH and promotes magnesium ammonium phosphate (struvite) and carbonate apatite crystallisation. Recurrent urease-producing urinary infection is associated with large branching calculi.
A. Escherichia coli: Escherichia coli commonly causes urinary and enteric infection, but the question tests a more characteristic alternative.
B. Staphylococcus epidermidis: Staphylococcus epidermidis forms biofilms on prostheses and lines but is less characteristic of this presentation.
D. Streptococcus pyogenes: Streptococcus pyogenes is group A beta-haemolytic streptococcus, classically linked to nonpurulent cellulitis, lymphangitis and pharyngitis.
Exam pearl: Proteus mirabilis — Commonest UTI organism is E. coli
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