Which toxin is produced by Clostridium botulinum and causes paralysis by blocking acetylcholine release?

• A. Diphtheria toxin
• B. Cholera toxin
• C. Tetanus toxin
• D. Botulinum toxin

Answer: (D)

Blocking acetylcholine release at the neuromuscular junction is the key idea. Botulinum toxin, produced by Clostridium botulinum, does exactly this: it cleaves SNARE proteins needed for synaptic vesicle fusion, so acetylcholine-containing vesicles cannot fuse with the presynaptic membrane and release ACh into the synaptic cleft. Without acetylcholine signaling, muscles can’t contract, leading to flaccid paralysis.

This differs from other toxins in the list. Diphtheria toxin inhibits protein synthesis by inactivating elongation factor EF-2. Cholera toxin increases cAMP in intestinal cells, causing secretory diarrhea. Tetanus toxin causes a different problem: it blocks inhibitory neurotransmitter release in the central nervous system, producing spastic, rigid paralysis.