clostridium, (genusClostridium), any of agenus of rod-shaped, usually gram-positivebacteria, 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, andtoxic chemicals and detergents. The species are variable in size. A typical species,Clostridium butyricum, ranges from 0.6μm across by 3 to 7 μm long.

Several species ofClostridium are important causes ofillness in humans and other animals.C. botulinum is the causative agent ofbotulism, which results from eating improperly sterilized canned foods that have become contaminated with thebotulinum toxin or which sometimes occurs as awound infection. Toxins produced byC. botulinum are the most potent poisons known. The toxin ofC. tetani causestetanus when introduced into damaged or dead tissue.C. perfringens,C. novyi, andC. septicum can causegangrene in humans.C. perfringens is also a source offoodborne illness, occurring on raw meat andpoultry. Other forms ofacuteclostridial infection commonly occur inlivestock andwaterfowl.