Clostridium, genus of rod-shaped, usually gram-positive bacteria, members of which are found in soil, water, and the intestinal tracts of humans and other animals. Most species grow only in the complete absence of oxygen. Dormant cells are highly resistant to heat, desiccation, and toxic chemicals and detergents. The species are variable in size. A typical species, C. butyricum, ranges from 0.6 micrometre across by 3 to 7 micrometres long. The toxins produced by C. botulinum, the causative agent of botulism, are the most potent poisons known. The toxin of C. tetani causes tetanus when introduced into damaged or dead tissue. C. perfringens, C. novyi, and C. septicum can cause gangrene in humans. Other forms of acute clostridial infection commonly occur in livestock and waterfowl.
— Botulinum neurotoxins (BoNTs) are the most potent natural toxins known. The family of BoNTs comprises of seven antigenically distinct serotypes (A to G) that are produced by various toxigenic strains of spore-forming anaerobic Clostridium botulinum. They act as metalloproteinases that enter peripheral cholinergic nerve terminals and cleave proteins that are crucial components of the neuroexocytosis apparatus, causing a persistent but reversible inhibition of neurotransmitter release resulting in flaccid muscle paralysis.