Bacteriology: Shigella: 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: Shigella

Sample item

A 5-year-old child has fever, tenesmus and blood-and-mucus stools. Stool culture on MacConkey agar grows pale non-lactose-fermenting colonies. The isolate is non-motile, produces no gas from glucose, and produces no hydrogen sulphide on triple sugar iron agar. Which organism is most likely?

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

The answer and the reasoning

D. Shigella species

Shigella are non-motile, non-lactose-fermenting, anaerogenic (no gas) and H2S-negative Enterobacterales that invade the colonic mucosa via M cells and cause bacillary dysentery. Salmonella and Proteus are motile, and Proteus is also a swarmer. Vibrio cholerae is a curved, motile, oxidase-positive organism that causes watery diarrhoea.

Option by option

  • A. Vibrio cholerae

    Vibrio cholerae is motile, oxidase-positive and causes painless watery stools rather than dysentery.

  • B. Salmonella Typhi

    Salmonella Typhi is motile and produces a small amount of hydrogen sulphide on triple sugar iron agar.

  • C. Proteus mirabilis

    Proteus mirabilis is motile, swarms on blood agar and is a strong H2S producer; it is a urinary pathogen.

  • D. Shigella species (correct)

    Correct. Non-motile, gas-negative and H2S-negative with pale colonies on MacConkey fits Shigella.

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 D, Shigella species. Shigella are non-motile, non-lactose-fermenting, anaerogenic (no gas) and H2S-negative Enterobacterales that invade the colonic mucosa via M cells and cause bacillary dysentery.

Why is "Vibrio cholerae" not the answer?

Vibrio cholerae is motile, oxidase-positive and causes painless watery stools rather than dysentery.

Why is "Salmonella Typhi" not the answer?

Salmonella Typhi is motile and produces a small amount of hydrogen sulphide on triple sugar iron agar.

Why is "Proteus mirabilis" not the answer?

Proteus mirabilis is motile, swarms on blood agar and is a strong H2S producer; it is a urinary pathogen.

What concept does this question test?

It tests Bacteriology: Shigella in Microbiology. Salmonella and Proteus are motile, and Proteus is also a swarmer. Vibrio cholerae is a curved, motile, oxidase-positive organism that causes watery diarrhoea.

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: Shigella?

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.