Botulinum toxin

A toxin produced by the bacterium Clostridium botulinum that is the most poisonous

biological substance known. Botulinum toxin acts as a neurotoxin. It binds to the nerve

ending at the point where the nerve joins a muscle, blocking the release by the nerve

of the chemical acetylcholine (the principal neurotransmitter at the neuromuscular

junction), preventing the muscle from contracting. The result is weakness and paralysis

of the muscle. The muscle atrophies. The blockage of acetylcholine release is

irreversible. Very small amounts of botulinum toxin can cause botulism in one of two

ways. One way is by ingesting the toxin itself (food borne botulism), as in canned

foods. The other way is by infection with the bacterial spores that produce and release

the toxin in the body (infectious botulism). The infection may occur in the intestine

(intestinal botulism), as in a newborn (infant botulism), or deep within a wound (wound

botulism). There is more than one type of botulinum toxin. Different strains of the

bacteria produce eight distinct neurotoxins. All eight types have a similar molecular

weight and structure, consisting of a heavy chain and a light chain joined by a disulfide

bond (most publications recognize only seven types; there are eight if the subtypes of

C, C1 and C2, are counted as separate types). All eight types act in a similar manner.

Only types A, B, E and F are known to cause botulism in humans. Botulinum toxin is

Bioterrorism agent category A.