Clostridium species are gram-positive or gram-variable, spore-forming, catalase-negative anaerobic bacilli. More than 100 species are currently recognized, though relatively few are encountered in properly collected clinical specimens from humans. There are three types of infection associated with Clostridium species:
- Non-invasive: Toxin-mediated
- Invasive: Progressive infection with tissue destruction
- Purulent disease: Closed space (e.g., in the peritoneal cavity) mixed infection with multiple organisms
Clostridium species are well known as the agents of these classic toxin-mediated diseases listed in Table 9.
Table 9. Toxin-Mediated Diseases Caused by Clostridium species.| Disease | Toxin Involved | Causative Organism |
| Tetanus or "lockjaw" | Tetanospasmin | Clostridium tetani |
| Myonecrosis/gas gangrene | Exotoxins | Clostridium perfringens |
| Botulism (severe food poisoning) | Botulin | Clostridium botulinum |
