Aeromonas hydrophila: a type of bacteria commonly found in freshwater or brackish water and in some fish and shellfish. It may cause stomach upset, diarrhea, and vomiting in some individuals if swallowed. It is more likely to cause intestinal symptoms in people with a suppressed immune system, such as people with cancer or those who are receiving immune-suppressing medications. The bacteria may also enter the body through an open wound that becomes contaminated with the organisms. In 2012, a severe case of necrotizing fasciitis occurred in a young woman due to Aeromonas hydrophila infection, resulting in the loss of one leg.