Cholera bacteria. Petri dish containing colonies of Vibrio cholerae bacteria. These water-borne pathogens are the cause of the disease cholera in humans. The bacteria are transmitted to humans in contaminated water and food. The bacteria infect the small intestine and produce a toxin that causes diarrhoea, leading to severe dehydration which may be fatal if untreated. Outbreaks are associated with poor sanitary conditions and are often epidemic. These bacteria have been cultured in a general purpose nutrient medium called tryptic soy agar (TSA).