Review of Human Pathogenic Bacteria in Marine Animals with Emphasis on Sharks

Bacteria belonging to the genus Vibn'o were demonstrated as etiologic agents of disease in captive sharks, following their isolation from a dead sandbar shark, Carcharhinus plumbeus, and from experimentally infected lemon sharks, Negaprion brevirostris. Studies were expanded to healthy, freeranging sharks captured and sampled for bacteria at Bimini, Bahamas. The bacterial flora of 28 neritic sharks, comprising five species, were examined. All 28 sharks were colonized with bacteria, primarily the genus Vibrio. All tissues and organs sampled contained Vibrio spp .• including liver, spleen, kidney, eye, mouth, skin, pancreas, intestine, stomach, gall bladder, gill slits, and fetuses (from a pregnant sharpnose). The conclusion, based on over 300 bacterial isolates from over 50 healthy sharks, is that sharks contain an autochthonous flora in most tissues and organs. The bacteria typically number between 102 and 105 bacteria per gram of tissue except blood, which is free from both aerobic and anaerobic bacteria. Human pathogens among the isolates included V. alginolyticus, V. parahaemolyticus, Listonella damsela, and Clostridium spp. While their ecological niche remains an enigma, it is clear that bacteria in healthy sharks can derive nutrients from elasmobranchs and, under conditions of stress to the host, cause death. Equally clear is the fact that when used as food, shark meat must be thoroughly cooked to destroy potential pathogens. If not properly cooked, pathogens such as V. parahaemolyticus could initiate gastroenteritis.