Clostridium (klo-strid-iŭm) n. a genus of mostly Gram-positive anaerobic spore-forming rodlike bacteria commonly found in soil and in the intestinal tract of humans and animals. C. botulinum a species that grows freely in badly preserved canned foods, producing a toxin causing serious food poisoning (see botulism). C. difficile (C. diff.) a species found in the intestine that causes pseudomembranous colitis, an increasingly common hospital-acquired infection. C. tetani a species that causes tetanus on contamination of wounds. C. perfringens (Welch's bacillus) a species that causes blood poisoning, food poisoning, and gas gangrene.
www.dh.gov.uk/en/Policyandguidance/Healthandsocialcaretopics/Healthcareacquiredinfection/Healthcareacquiredgeneralinformation/DH_4115800 A guide to Clostridium difficile from the Department of Health, including the ways in which it can cause infection

Clostridium A genus of endospore-forming, typically Gram-positive bacteria in which the cells are rod-shaped and usually motile. They are chemo-organotrophic, and most species can grow only in the absence of air. There are many species, found in soil, in aquatic habitats, in animal intestines, etc. The genus includes some important pathogens, e.g. the causal agents of botulism, tetanus, and gas gangrene.

Clostridium A genus of bacteria, of which C. botulinum is responsible for botulism, a rare but often fatal form of food poisoning. It is found widely distributed in soil; during growth on favourable food materials, the organism synthesizes an extremely potent neurotoxin which is released into the food when the cell dies. The spores are extremely heat‐resistant and their thermal death time is used as a minimum standard for processing foods with pH values higher than 4.5.