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.

Try it

Microbiology · Bacterial toxins

Sample item

A farmer with a deep soil-contaminated wound develops trismus, risus sardonicus and painful spasms. What is the mechanism of the toxin responsible?

AActivates adenylate cyclase through ADP-ribosylation of a G proteinBInactivates elongation factor 2CBlocks release of acetylcholine at the neuromuscular junctionDBlocks release of the inhibitory neurotransmitters glycine and GABA

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

The answer and the reasoning

D. Blocks release of the inhibitory neurotransmitters glycine and GABA

Tetanospasmin of Clostridium tetani travels by retrograde axonal transport to the spinal cord and cleaves synaptobrevin, preventing release of glycine and GABA from inhibitory interneurons. Motor neurons are then unopposed, causing spastic paralysis.

Option by option

A. Activates adenylate cyclase through ADP-ribosylation of a G protein
Raising cAMP through G protein modification is the action of cholera toxin.
B. Inactivates elongation factor 2
Inactivating elongation factor 2 is the action of diphtheria toxin.
C. Blocks release of acetylcholine at the neuromuscular junction
Blocking acetylcholine release is the action of botulinum toxin, producing flaccid paralysis.
D. Blocks release of the inhibitory neurotransmitters glycine and GABA (correct)
Correct. Loss of inhibition produces rigidity and spasms.

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.

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is D, Blocks release of the inhibitory neurotransmitters glycine and GABA. Tetanospasmin of Clostridium tetani travels by retrograde axonal transport to the spinal cord and cleaves synaptobrevin, preventing release of glycine and GABA from inhibitory interneurons.

Why is "Activates adenylate cyclase through ADP-ribosylation of a G protein" not the answer?

Raising cAMP through G protein modification is the action of cholera toxin.

Why is "Inactivates elongation factor 2" not the answer?

Inactivating elongation factor 2 is the action of diphtheria toxin.

Why is "Blocks release of acetylcholine at the neuromuscular junction" not the answer?

Blocking acetylcholine release is the action of botulinum toxin, producing flaccid paralysis.

What concept does this question test?

It tests Bacterial toxins in Microbiology. Motor neurons are then unopposed, causing spastic paralysis.

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.