Botulisme

Botulism is a severe neuroparalytic illness caused by the botulinum toxin, which is produced by Clostridium botulinum.

In adults, it occurs either after consuming food contaminated with preformed toxin or when the bacterium infects a wound and produces the toxin locally.

In localized infection, the bacterium synthesizes an inactive form of the botulinum toxin, composed of a heavy and a light chain linked by a disulfide bond.

When the toxin is ingested, it crosses intestinal epithelial cells through transcytosis and enters the bloodstream.

From there, it spreads into neuromuscular junctions and targets nerve endings that release acetylcholine.

The toxin enters the nerve cell through endocytosis.

Endosome acidification triggers cleavage of the disulfide bond, releasing the catalytically active light chain into the cytosol.

The light chain acts as a protease that cuts SNARE proteins needed for synaptic vesicle fusion and acetylcholine release.

Blocking acetylcholine release prevents muscle contraction, leading to weakness and flaccid paralysis.