Because infections originating in the intestine usually include Bacteroides fragilis, which is resistant to penicillin, other antibiotics are used. Many anaerobic infections are caused by clostridia, which produce various toxins that damage tissue or the nervous system. The most common clostridial infections are short-lived and relatively mild food poisonings. In addition, clostridia may cause inflammation that sometimes destroys the walls of the large and small intestine, a condition called necrotizing enteritis. Although this infection can occur as an isolated case, it may also occur in outbreaks caused by eating contaminated meat.
Clostridia also infect wounds.
Botulism occurs from eating food contaminated with a toxin produced by some clostridia. Severe illness often results from clostridial infections, which can be complicated by deep tissue destruction. The risk of death is high, especially in people with cancer and the elderly. Spasm of the jaw muscles accounts for the name lockjaw. Although it is becoming rare in the United States, tetanus occurs in many parts of the world, especially in developing countries.