Clostridia

Pathogenic Clostridia

Clostridium botulinum

Clostridia 

The genus Clostridium consists of relatively large, Gram-positive, rod-shaped bacteria in the Phylum Firmicutes (Clostridia is actually a Class in the Phylum). All species form endospores and have a strictly fermentative type of metabolism. Most clostridia will not grow under aerobic conditions and vegetative cells are killed by exposure to O₂, but their spores are able to survive long periods of exposure to air.

The clostridia are ancient organisms that live in virtually all of the anaerobic habitats of nature where organic compounds are present, including soils, aquatic sediments and the intestinal tracts of animals.

Clostridia are able to ferment a wide variety of organic compounds. They produce end products such as butyric acid, acetic acid, butanol and acetone, and large amounts of gas (CO₂ and H₂) during fermentation of sugars. A variety of foul smelling compounds are formed during the fermentation of amino acids and fatty acids. The clostridia also produce a wide variety of extracellular enzymes to degrade large biological molecules (e.g. proteins, lipids, collagen, cellulose, etc.) in the environment into fermentable components. Hence, the clostridia play an important role in nature in biodegradation and the carbon cycle. In anaerobic clostridial infections, these enzymes play a role in invasion and pathology.

Most of the clostridia are saprophytes, but a few are pathogenic for humans, primarily Clostridium perfringens, C. difficile, C. tetani and C. botulinum. Those that are pathogens have primarily a saprophytic existence in nature and, in a sense, are opportunistic pathogens. Clostridium tetani and Clostridium botulinumproduce the most potent biological toxins known to affect humans. As pathogens of tetanus and food-borne botulism, they owe their virulence almost entirely to their toxigenicity. Other clostridia, however, are highly invasive under certain circumstances.

Stained pus from a mixed anaerobic infection. At least three different clostridia are apparent.