Clostridium botulinum: A group of gram-positive, rod-shaped bacteria commonly found in the soil that grow best in anaerobic (in the absence of oxygen) conditions. The bacteria form heat-resistant spores which allow them to survive in a dormant state until exposed to conditions that can support their growth. Clostridium botulinum produces botulinum toxin, a highly potent neurotoxin and the cause of the disease botulism.
Clostridium botulinum and its spores are widely distributed in nature. They occur in both cultivated and forest soils, bottom sediments of streams, lakes, and coastal waters, and in the intestinal tracts of fish and mammals, and in the gills and viscera of crabs and other shellfish. They may be present on the surface of fruits and vegetables.
See also: botulinum toxin, botulism