Clostridia are prokaryotic bacteria of the phylum Firmicutes, which are large, anaerobic, spore-forming, rod-shaped, gram-positive organisms. They can be living cells (vegetative forms) or dormant spores. Their natural habitats are soils and intestinal tracts of animals, including humans.
Dormant spores of several clostridial species have been found in healthy muscular tissue of horses and cows. The endospores are oval, sometimes spherical, and are located centrally, subterminally, or terminally. The vegetative forms of clostridia in tissue fluids of infected animals occur singly, in pairs, or rarely in chains.
Differentiation of the various pathogenic and related species is based on morphological characteristics in culture including spore shape and position, biochemical testing, and the antigenic specificity of toxins or surface antigens. The genomes of many clostridial spp have been sequenced and published. Pathogenic strains or their toxins may be acquired by susceptible animals via either wound contamination or ingestion. Diseases thus produced are a constant threat to successful food animal production worldwide.
Clostridial diseases can be divided into two categories:
Clostridial diseases are not spread from animal to animal or from animals to humans. They have been classified into three forms: