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 therelease by the nerve of the chemical acetylcholine, preventing the muscle from contracting. The result is weakness andparalysis of the muscle. The muscle atrophies. The blockage of acetylcholine release is irreversible. Function can berecovered by the sprouting of nerve terminals and the formation of new synaptic contacts, which usually takes 2 to 3months. Very small amounts of botulinum toxin can cause botulism in one of two ways. One way is by ingesting the toxinitself (food borne botulism), as in canned foods. The other way is by infection with the bacterial spores that produce andrelease the toxin in the body (infectious botulism). The infection may occur in the intestine (intestinal botulism), as in anewborn, or deep within a wound (wound botulism). There is more than one type of botulinum toxin. Different strains of thebacteria produce seven distinct neurotoxins designated A through G. All seven types have a similar molecular weight andstructure, consisting of a heavy chain and a light chain joined by a disulphide bond. All seven types act in a similarmanner. Only types A, B, E and F are known to cause botulism in humans. The toxin is heat labile and can be destroyedheated at 80 °C for 10 minutes or longer. See: Botox.