A bacterial genus in the family Vibrionaceae comprising oxidase-positive, facultatively anaerobic, monotrichously flagellated gram-negative rods. The mesophilic species are A. hydrophila, A. caviae and A. sobria; the psychrophilic one is A. salmonicida. Aeromonads are of aquatic origin and are found in surface and waste water but not in seawater. They infect chiefly cold-blooded animals such as fishes, reptiles, and amphibians and only occasionally warm-blooded animals and humans.