Vibrio parahaemolyticus: Kanagawa phenomenon: 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 parahaemolyticus: Kanagawa phenomenon

Sample item

A man develops watery diarrhoea and abdominal cramps after eating raw shellfish. A halophilic Vibrio from stool causes beta-haemolysis on Wagatsuma agar containing human red cells. Which factor causes this Kanagawa phenomenon?

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

The answer and the reasoning

B. Thermostable direct haemolysin

Pathogenic strains of Vibrio parahaemolyticus produce thermostable direct haemolysin, which lyses human red cells on Wagatsuma agar, the Kanagawa phenomenon. Most clinical isolates are Kanagawa positive, whereas most environmental isolates are negative. The organism grows green on TCBS agar.

Option by option

  • A. Cholera toxin

    Cholera toxin is produced by Vibrio cholerae and not responsible for haemolysis.

  • B. Thermostable direct haemolysin (correct)

    Correct. Thermostable direct haemolysin accounts for the Kanagawa phenomenon.

  • C. Heat-labile enterotoxin

    Heat-labile enterotoxin belongs to ETEC and does not cause the Kanagawa reaction.

  • D. Shiga toxin

    Shiga toxin is produced by Shigella dysenteriae and EHEC.

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, Thermostable direct haemolysin. Pathogenic strains of Vibrio parahaemolyticus produce thermostable direct haemolysin, which lyses human red cells on Wagatsuma agar, the Kanagawa phenomenon.

Why is "Cholera toxin" not the answer?

Cholera toxin is produced by Vibrio cholerae and not responsible for haemolysis.

Why is "Heat-labile enterotoxin" not the answer?

Heat-labile enterotoxin belongs to ETEC and does not cause the Kanagawa reaction.

Why is "Shiga toxin" not the answer?

Shiga toxin is produced by Shigella dysenteriae and EHEC.

What concept does this question test?

It tests Vibrio parahaemolyticus: Kanagawa phenomenon in Microbiology. Most clinical isolates are Kanagawa positive, whereas most environmental isolates are negative. The organism grows green on TCBS agar.

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 Vibrio parahaemolyticus: Kanagawa phenomenon?

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.