Bacteriology: enteric pathogens: 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: enteric pathogens

Sample item

A 4-year-old child develops bloody diarrhoea after eating undercooked beef. Five days later he has pallor, reduced urine output, a raised creatinine and schistocytes with thrombocytopenia. Which organism and which culture medium help identify it?

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

The answer and the reasoning

C. Escherichia coli O157:H7, which does not ferment sorbitol on sorbitol MacConkey agar

Shiga toxin-producing E. coli O157:H7 causes haemorrhagic colitis and haemolytic uraemic syndrome through Shiga toxin acting on the endothelium. Unlike most E. coli it does not ferment sorbitol, so it forms colourless colonies on sorbitol MacConkey agar. Antibiotics are avoided because they may increase toxin release.

Option by option

  • A. Vibrio cholerae, which grows on TCBS agar

    Vibrio cholerae causes watery diarrhoea, not bloody diarrhoea with HUS.

  • B. Shigella dysenteriae, which forms lactose-fermenting colonies on MacConkey agar

    Shigella is a non-lactose fermenter; HUS can follow S. dysenteriae type 1 infection, but the undercooked-beef history points to E. coli O157:H7.

  • C. Escherichia coli O157:H7, which does not ferment sorbitol on sorbitol MacConkey agar (correct)

    Correct. Sorbitol non-fermentation is the screening feature of this pathogen.

  • D. Salmonella Typhi, which grows on bismuth sulphite agar

    Salmonella Typhi causes enteric fever.

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 C, Escherichia coli O157:H7, which does not ferment sorbitol on sorbitol MacConkey agar. Shiga toxin-producing E.

Why is "Vibrio cholerae, which grows on TCBS agar" not the answer?

Vibrio cholerae causes watery diarrhoea, not bloody diarrhoea with HUS.

Why is "Shigella dysenteriae, which forms lactose-fermenting colonies on MacC…" not the answer?

Shigella is a non-lactose fermenter; HUS can follow S. dysenteriae type 1 infection, but the undercooked-beef history points to E. coli O157:H7.

Why is "Salmonella Typhi, which grows on bismuth sulphite agar" not the answer?

Salmonella Typhi causes enteric fever.

What concept does this question test?

It tests Bacteriology: enteric pathogens in Microbiology. coli O157:H7 causes haemorrhagic colitis and haemolytic uraemic syndrome through Shiga toxin acting on the endothelium. Unlike most E. coli it does not ferment sorbitol, so it forms colourless colonies on sorbitol MacConkey agar. Antibiotics are avoided because they may increase toxin release.

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 Bacteriology: enteric pathogens?

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.