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the etiologic agent of human cholera, found in the intestinal tract of normal and diseased humans and animals and in water. The species is divided into serogroups on the basis of somatic (O) antigens; serogroups are further divided into serovars and biogroups. Only serogroups O1 and O139 cause clinical disease, producing an enterotoxin that promotes secretion of fluid and electrolytes by the small intestine.Medical dictionary. 2011.