Biochemical and Biological Properties of Motile Aeromonas Isolated from Aquatic Environments

A total of 97 strains of motile Aeromonas species were isolated from 42 (55.3%) out of 76 aquatic environmental samples. Sampling sites included rivers, wells and coastal sea. Fiftyeight strains from 10 samples, 17 from 11 and 11 from 10 samples were identified as Aeromonas caviae, A. hydrophila, and A. sobria, respectively. The species of the remaining 11 isolates from 10 samples have not been identified so far.All isolates of A. hydrophila and A. sobria, and 2 of A. caviae, were shown to be lysine decarboxylase-positive by means of the ninhydrin test. All isolates but one were sensitive to tetracycline, chloramphenicol, nalidixic acid and gentamicin, but the majority of isolates were resistant to ampicillin.All A. hydrophila isolates exhibited hemolytic activity, 94% were cytotoxic and 53% were found to be enterotoxic. For A. sobria, 82% were hemolytic, 91% were cytotoxic and 73% showed enterotoxic activity. These biological activities, however, were inactivated by heat treatment at 56°C for 10min. None of the isolated A. caviae showed these activities.SDS-PAGE profiles of whole-cell preparations of 62 Aeromonas isolates showed common major bands as well as specific bands within genus and species. This result suggests the possibility of distinguishing species by this method.