Clostridia are anaerobic, spore-forming, gram-positive bacilli that exist widely in nature, being found in dust, soil, vegetation, and the gastrointestinal tracts of humans and animals. Though nearly 100 Clostridium spp have been identified, only 25 to 30 are recognized as relatively commonly inducing disease in humans or animals. The pathogenic species, in the vegetative form, produce various tissue-destructive and neural exotoxins that have been biochemically and serologically delineated.