General microbiology and sterilisation: phage typing: 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 · General microbiology and sterilisation: phage typing

Sample item

Several cases of typhoid appear in one hostel, and the public health laboratory wants to know whether all isolates come from a single source. Which typing method, classically used for Salmonella Typhi, compares isolates by their pattern of susceptibility to a standard panel of Vi-specific agents?

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

The answer and the reasoning

C. Bacteriophage typing

Vi phage typing divides Salmonella Typhi into types and helps trace the source of an outbreak or a carrier. It is an epidemiological marker, not a diagnostic test for the patient. Newer molecular typing has largely replaced it.

Option by option

  • A. Kauffmann-White serotyping

    Kauffmann-White serotyping classifies Salmonella by O, H and Vi antigens, not by phage lysis.

  • B. Disc diffusion susceptibility

    Disc diffusion tests antibiotic susceptibility and is not a source-tracing tool.

  • C. Bacteriophage typing (correct)

    Correct. Phage typing compares isolates by their pattern of lysis by a phage panel.

  • D. Widal agglutination

    Widal detects patient antibodies and does not compare isolates.

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 C, Bacteriophage typing. Vi phage typing divides Salmonella Typhi into types and helps trace the source of an outbreak or a carrier.

Why is "Kauffmann-White serotyping" not the answer?

Kauffmann-White serotyping classifies Salmonella by O, H and Vi antigens, not by phage lysis.

Why is "Disc diffusion susceptibility" not the answer?

Disc diffusion tests antibiotic susceptibility and is not a source-tracing tool.

Why is "Widal agglutination" not the answer?

Widal detects patient antibodies and does not compare isolates.

What concept does this question test?

It tests General microbiology and sterilisation: phage typing in Microbiology. It is an epidemiological marker, not a diagnostic test for the patient. Newer molecular typing has largely replaced it.

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 General microbiology and sterilisation: phage typing?

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.