What is the name of the toxin produced by Clostridium tetani?

The toxin produced by Clostridium tetani is tetanospasmin.

Tetanospasmin, also called tetanus toxin or tetanus neurotoxin, is made by growing C. tetani cells, especially in oxygen-poor wounds. The bacterium’s durable spores are common in soil and can enter the body through punctures, burns, or contaminated injuries. Not every strain produces the toxin: the gene is carried on a plasmid found in many strains.

The toxin travels through the nervous system and blocks the release of inhibitory neurotransmitters, chiefly glycine and GABA. Without those braking signals, motor neurons become overactive, producing painful muscle stiffness and spasms. Lockjaw, or trismus, is the classic early sign, but the spasms can spread throughout the body.

Tetanospasmin is often confused with tetanolysin, another toxin made by C. tetani whose role in disease is less clear. Botulinum toxin is related but has the opposite broad effect: it prevents muscle contraction and causes flaccid paralysis. Tetanus vaccines contain inactivated tetanospasmin, called tetanus toxoid, which trains immunity without causing the toxin’s effects.