Bacteriology: practice question

A Microbiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Microbiology · Bacteriology

Sample item

A man develops profuse watery diarrhoea with fever and abdominal pain, and colonoscopy shows yellow-white plaques on the mucosa, after a course of clindamycin. Which investigation is most appropriate?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Stool assay for Clostridioides difficile toxin or toxin gene

Antibiotic disruption of colonic flora allows C. difficile overgrowth. Toxins A (enterotoxin) and B (cytotoxin) cause pseudomembranous colitis. Diagnosis rests on detecting toxin in stool, usually with glutamate dehydrogenase screening and toxin or PCR confirmation. Oral vancomycin or fidaxomicin is used to treat.

Option by option

  • A. Stool culture on MacConkey agar

    MacConkey culture would grow coliforms and cannot detect an anaerobic toxin-producer.

  • B. Stool assay for Clostridioides difficile toxin or toxin gene (correct)

    Correct. The diagnosis rests on stool toxin or toxin gene detection.

  • C. Stool microscopy for ova and cysts

    Microscopy for ova and cysts diagnoses parasitic infection.

  • D. Blood culture for Salmonella typhi

    Blood culture is for enteric fever, which is not suggested after clindamycin.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

More Microbiology questions

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is B, Stool assay for Clostridioides difficile toxin or toxin gene. Antibiotic disruption of colonic flora allows C.

Why is "Stool culture on MacConkey agar" not the answer?

MacConkey culture would grow coliforms and cannot detect an anaerobic toxin-producer.

Why is "Stool microscopy for ova and cysts" not the answer?

Microscopy for ova and cysts diagnoses parasitic infection.

Why is "Blood culture for Salmonella typhi" not the answer?

Blood culture is for enteric fever, which is not suggested after clindamycin.

What concept does this question test?

It tests Bacteriology in Microbiology. difficile overgrowth. Toxins A (enterotoxin) and B (cytotoxin) cause pseudomembranous colitis. Diagnosis rests on detecting toxin in stool, usually with glutamate dehydrogenase screening and toxin or PCR confirmation. Oral vancomycin or fidaxomicin is used to treat.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Bacteriology?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.