Neurotoxin-producing group of Clostridium spp.

Two clostridial species, Clostridium botulinum and Clostridium tetani, make up this group of organisms. Both are typical members of the genus, have strict anaerobic growth requirements, and their vegetative forms produce a toxin or toxins, which, in the case of C. botulinum, are among the most toxic biological substances known. Although botulism and tetanus are both caused by neurotoxins, the diseases differ markedly in respect of their epidemiology, pathogenesis and clinical signs. Both affect humans and livestock in many parts of the world, are almost invariably fatal, and may have grave economic effects on properties where outbreaks occur.

Clostridium botulinum comprises a group of metabolically diverse bacilli that produce seven pharmacologically similar, but serologically distinct, neurotoxins, collectively referred to as botulinum toxin. Except in cases of the rare toxic-infectious form of botulism in which the toxin is produced by bacteria proliferating in the live animal or human body, it is ingested in feed or water contaminated by decomposing carcass or organic material in which it has been produced. Of the livestock species cattle, sheep, goats and horses are susceptible to the effects of the toxin while pigs are almost totally resistant.

The disease, which is really an intoxication, is characterized by the development of a profound, usually fatal, flaccid paralysis which is the consequence of the irreversible binding of botulinum toxin to peripheral nerve endings, and blocking of neurotransmission by acetylcholine.

Clostridium tetani, on the other hand, proliferates in necrotic foci, most often in deep, penetrating wounds in which the redox potential is low enough to allow growth of the anaerobic organism. Tetanus toxin, also known as tetanospasmin, produced at these sites is absorbed by nerve endings and transported to the central nervous system, where it exterts its effects. Tetanus toxin irreversibly blocks inhibitory neurons (where the neurotransmitters are glycine or gamma-aminobutyric acid) in the spinal cord and prevents the contraction of antagonistic muscles, thus causing a state of constant muscular spasticity. Death is usually the result of asphyxiation. Sheep and horses are the livestock species most commonly affected by tetanus.

Both botulism and tetanus can be effectively controlled by immunization.