Vibrio cholerae: biotype differentiation: 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 · Vibrio cholerae: biotype differentiation

Sample item

During a cholera outbreak, a Vibrio cholerae isolate agglutinates with O1 antiserum, is Voges-Proskauer positive and grows around a 50 unit polymyxin B disc. Which type is it?

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

The answer and the reasoning

D. Vibrio cholerae O1, El Tor biotype

The El Tor biotype is polymyxin B resistant, Voges-Proskauer positive and usually haemolytic, unlike the classical biotype. Agglutination with O1 antiserum places it in serogroup O1 rather than O139. El Tor caused the seventh cholera pandemic.

Option by option

  • A. Non-O1, non-O139 Vibrio cholerae

    Non-O1 strains do not agglutinate with O1 antiserum.

  • B. Vibrio cholerae O1, classical biotype

    The classical biotype is inhibited by polymyxin B and is Voges-Proskauer negative.

  • C. Vibrio cholerae O139

    O139 would not agglutinate with O1 antiserum.

  • D. Vibrio cholerae O1, El Tor biotype (correct)

    Correct. Polymyxin resistance and a positive Voges-Proskauer test identify El Tor.

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 D, Vibrio cholerae O1, El Tor biotype. The El Tor biotype is polymyxin B resistant, Voges-Proskauer positive and usually haemolytic, unlike the classical biotype.

Why is "Non-O1, non-O139 Vibrio cholerae" not the answer?

Non-O1 strains do not agglutinate with O1 antiserum.

Why is "Vibrio cholerae O1, classical biotype" not the answer?

The classical biotype is inhibited by polymyxin B and is Voges-Proskauer negative.

Why is "Vibrio cholerae O139" not the answer?

O139 would not agglutinate with O1 antiserum.

What concept does this question test?

It tests Vibrio cholerae: biotype differentiation in Microbiology. Agglutination with O1 antiserum places it in serogroup O1 rather than O139. El Tor caused the seventh cholera pandemic.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Vibrio cholerae: biotype differentiation?

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.