Clinical microbiology and hospital infection control: molecular typing in outbreaks: 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 · Clinical microbiology and hospital infection control: molecular typing in outbreaks

Sample item

Four MRSA isolates from different patients in one ward have identical antibiograms. Which method best shows whether they belong to a single clone?

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

The answer and the reasoning

B. Whole-genome sequencing or pulsed-field gel electrophoresis

Identical antibiograms do not prove relatedness because many unrelated strains share a resistance pattern. Molecular typing, such as whole-genome sequencing, PFGE or MLST, determines clonal relationship in outbreak investigation.

Option by option

  • A. Gram stain morphology of each isolate

    All S. aureus look alike on Gram stain.

  • B. Whole-genome sequencing or pulsed-field gel electrophoresis (correct)

    Correct. Genome-based typing resolves strain relatedness.

  • C. Repeating the disc diffusion test

    Repeating the antibiogram only reproduces the same pattern.

  • D. Catalase test on each isolate

    Every S. aureus isolate is catalase positive, so it cannot discriminate strains.

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, Whole-genome sequencing or pulsed-field gel electrophoresis. Identical antibiograms do not prove relatedness because many unrelated strains share a resistance pattern.

Why is "Gram stain morphology of each isolate" not the answer?

All S. aureus look alike on Gram stain.

Why is "Repeating the disc diffusion test" not the answer?

Repeating the antibiogram only reproduces the same pattern.

Why is "Catalase test on each isolate" not the answer?

Every S. aureus isolate is catalase positive, so it cannot discriminate strains.

What concept does this question test?

It tests Clinical microbiology and hospital infection control: molecular typing in outbreaks in Microbiology. Molecular typing, such as whole-genome sequencing, PFGE or MLST, determines clonal relationship in outbreak investigation.

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 Clinical microbiology and hospital infection control: molecular typing in outbreaks?

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.