Bacteriology: Clostridioides difficile: 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: Clostridioides difficile

Sample item

Watery diarrhoea and pseudomembranes develop after clindamycin treatment. Which test best supports infection by toxigenic Clostridioides difficile?

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

The answer and the reasoning

B. Detection of toxin genes or toxin in unformed stool

C. difficile diagnosis is made in symptomatic patients using an assay for toxigenic organisms or toxin on unformed stool. Colonisation is common, so testing formed stool or asymptomatic patients can mislead.

Option by option

  • A. Urease testing of stool

    Urease testing is not used for C. difficile diagnosis.

  • B. Detection of toxin genes or toxin in unformed stool (correct)

    Correct. The clinically relevant diagnosis is toxin-producing C. difficile in diarrhoeal stool.

  • C. Serum antistreptolysin O titre

    ASO indicates recent streptococcal exposure.

  • D. Culture of a formed stool sample alone

    Culture alone does not establish toxin production or disease.

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.

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Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is B, Detection of toxin genes or toxin in unformed stool. C.

Why is "Urease testing of stool" not the answer?

Urease testing is not used for C. difficile diagnosis.

Why is "Serum antistreptolysin O titre" not the answer?

ASO indicates recent streptococcal exposure.

Why is "Culture of a formed stool sample alone" not the answer?

Culture alone does not establish toxin production or disease.

What concept does this question test?

It tests Bacteriology: Clostridioides difficile in Microbiology. difficile diagnosis is made in symptomatic patients using an assay for toxigenic organisms or toxin on unformed stool. Colonisation is common, so testing formed stool or asymptomatic patients can mislead.

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: Clostridioides difficile?

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.