Aeromonas spp. are natural inhabitants of aquatic environments worldwide. These Gram-negative, nonspore-forming facultatively anaerobic, glucose-fermenting organisms have been isolated from groundwater, treated drinking water, surface waters, wastewater, sludge, and sediment. Their populations are seasonal in all natural waters, though the highest numbers are present in warmer months. Aeromonads cause serious diseases of aquatic animals and represent an economic threat to the aquaculture industry. Some species among the motile aeromonads have emerged as a potential microbial threat to human populations, especially the immunocompromised.1
As a result of taxonomic studies, Aeromonas bacteria were removed from the family Vibrionaceae and established as a genus of the new family Aeromonadaceae. The genus Aeromonas comprises 22 phenospecies and 18 genomospecies, 3 of which are unnamed.2 Phenotypic characterization of genomospecies has advanced via incorporation of nontraditional substrates into biochemical identification schema. Environmental microbiologists usually combine all motile, mesophilic aeromonads into the Aeromonas hydrophila complex, or simply report isolates as A. hydrophila. These practices obscure understanding of the medical and public health significance of aeromonads isolated from clinical specimens, environmental samples, and public water supplies; identification of Aeromonas isolates according to established taxonomic principles is preferable.3 Aeromonas hydrophila (HG-1), caviae (HG-4), veronii (HG-8), jandaei (HG-9), schubertii (HG-12), and trota (HG-14) are most frequently associated with clinical specimens.2