n. a false membrane, consisting of a layer of exudate on the surface of the skin or a mucous membrane. In diphtheria a pseudomembrane forms in the throat. In pseudomembranous colitis, a disease caused by *Clostridium difficile that usually follows antibiotic therapy, pseudomembranes develop in the colon, resulting in profuse diarrhoea.
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. Many species cause disease and produce extremely potent *exotoxins. C. botulinum grows freely in badly preserved canned foods, producing a toxin causing serious food poisoning (*botulism); an extremely dilute form of this toxin is now used to treat muscle spasm (see botulinum toxin). C. histolyticum, C. oedematiens, and C. septicum all cause *gas gangrene when they infect wounds. C. tetani lives as a harmless *commensal in the intestine but causes *tetanus on contamination of wounds (with manured soil). The species C. perfringens – Welch’s bacillus – causes blood poisoning, *food poisoning, and gas gangrene. Overgrowth of Clostridium difficile (often shortened to C. diff), a normal inhabitant of the human large intestine, is not uncommon as a complication of some antibiotic therapy and produces a specific condition – pseudomembranous colitis (see pseudomembrane) – which is life-threatening unless treated promptly and is becoming more common as a hospital-acquired infection.... clostridium
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