CHARACTERISTICS: Vibrio cholerae is a gram negative, non-spore forming, curved rod that is oxidase positive. It is very motile and has a single polar flagellum. The bacterium is 1- 3 µm by 0.5-0.8 µm, is a facultative anaerobe and is part of the Vibronaceae family. Serogroups O1 (classical and El Tor biotypes) and O139 are primarily responsible for cholera outbreaks. Pathogenic serogroups produce cholera toxin (CT) while non pathogenic strains may or may not produce this toxin. Recently,V. cholerae serougroup O75 strains possessing the cholera toxin gene were isolated from patients with severe diarrhoea, and serogroup O141 has been associated with sporadic cholera-like diarrhoea and bloodstream infections in the United States. Some serotypes may serve as a reservoir for the cholera toxin phage genome. Serotypes that do not produce cholera toxin can still cause illness in humans (i.e. enteritis).