Evaluation of different assay systems for identification of environmental Aeromonas strains

Important biochemical reactions in conventional tests were compared with counterpart reactions in two multiple test systems, API-20E (Analytab Products, Plainview, N.Y.) and Aeromonas hydrophila medium, to evaluate their accuracy for the identification of motile Aeromonas spp. isolated from fish. In a total of 49 Aeromonas spp. isolates and 10 A. hydrophila reference strains, false-negative or -positive reactions were detected in the Voges-Proskauer test, indole production, gelatinase activity, production of gas, fermentation of arabinose, and lysine decarboxylase reaction. A good correlation was found, among the three identification systems, for the fermentation of mannitol and inositol as well as for the arginine dihydrolase and ornithine decarboxylase tests. The failure of A. hydrophila medium in the detection of gas indicates that this medium is not entirely suitable for defining aerogenic or anaerogenic strains. From the results of the present study, we consider that of the identification method and taxonomic scheme to be adopted for environmental Aeromonas spp. must be standardized.