The members of the genus Aeromonas are Gram-negative fac-ultative anaerobic bacilli that morphologically resemble other members of the family Vibrionaceae. At least 16 species of Aeromonas have been described, of which 11 species are asso-ciated with human disease. Aeromonas hydrophila, Aeromonascaviae, Aeromonas veronii, Aeromonas schubertii, and Aeromonas jandaii are most important species. Aeromonas spp. are Gram-negative motile bacilli with the presence of polar flagella. Few strains are nonmotile. They are catalase positive, oxidase posi-tive, and nitrate positive. They ferment sugars with production of both acid and gas. They grow at an optimum temperature of 32°C and at a pH of 7.
Aeromonas spp. are widely distributed in brackish water andin soil. Aeromonas species produce many virulence factors, such as enterotoxin, endotoxins, hemolysin, protease, siderophores, and adherence factors. However, the exact role of these virulence factors in the pathogenesis of illness is not known. Aeromonas spp. in humans cause gastroenteritis and wound infections.
· Gastroenteritis occurs following ingestion of contaminated food or water. The condition in adults manifests as chronic diarrhea, while in children it presents as acute and severe illness manifested by dysentery with presence of blood and mucus in the stool. Acute diarrhea is a self-limiting condition.
· Wound infection is caused by exposure of the broken skin to contaminated water. Aeromonas spp. also cause opportunis-tic skin diseases in immunocompromised patients, such as patients with malignancy or hepatobiliary disease.
Aeromonas species are known to colonize intestinal tractof humans in approximately 3% of individuals. Therefore, isolation of the bacteria from stool by culture does not indi-cate disease by Aeromonas species. It needs careful interpreta-tion by taking into consideration clinical presentation of the illness.
Aeromonas species are susceptible to chloramphenicol, gen-tamicin, and trimethoprim–sulfamethoxazole. They are resis-tant to penicillins, most cephalosporins, and erythromycin.