Bacterial toxins: 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 · Bacterial toxins

Sample item

A patient has profuse painless watery diarrhoea resembling rice water. Which action of cholera toxin explains the fluid loss?

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

The answer and the reasoning

C. ADP-ribosylation of the Gs protein, raising intracellular cAMP in enterocytes

The A subunit of cholera toxin ADP-ribosylates Gs, locking adenylate cyclase on and raising cAMP. This opens chloride channels in crypt cells, so chloride and water pour into the lumen without mucosal destruction.

Option by option

  • A. Cleavage of SNARE proteins

    SNARE cleavage describes botulinum and tetanus toxins.

  • B. Inhibition of the 60S ribosomal subunit

    Inhibition of the 60S subunit describes Shiga toxin, which causes bloody diarrhoea.

  • C. ADP-ribosylation of the Gs protein, raising intracellular cAMP in enterocytes (correct)

    Correct. Persistent adenylate cyclase activation drives secretion of chloride and water.

  • D. Pore formation in the cell membrane

    Pore formation is the mode of action of toxins such as staphylococcal alpha toxin.

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, ADP-ribosylation of the Gs protein, raising intracellular cAMP in enterocytes. The A subunit of cholera toxin ADP-ribosylates Gs, locking adenylate cyclase on and raising cAMP.

Why is "Cleavage of SNARE proteins" not the answer?

SNARE cleavage describes botulinum and tetanus toxins.

Why is "Inhibition of the 60S ribosomal subunit" not the answer?

Inhibition of the 60S subunit describes Shiga toxin, which causes bloody diarrhoea.

Why is "Pore formation in the cell membrane" not the answer?

Pore formation is the mode of action of toxins such as staphylococcal alpha toxin.

What concept does this question test?

It tests Bacterial toxins in Microbiology. This opens chloride channels in crypt cells, so chloride and water pour into the lumen without mucosal destruction.

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 Bacterial toxins?

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.