Phenotypic methods for speciating clinical Aeromonas isolates.

AIMS To establish the suitability of currently available phenotypic methods for speciation of clinical Aeromonas isolates in diagnostic microbiology laboratories. METHODS Using 62 Aeromonas spp, three schemes based on biochemical reactions were compared: a series of conventional tests; a system based on the suicide phenomenon, comprising two tubes in total; and a commercially available test, API 20 NE, augmented with a plate assay for beta haemolysin production. The whole cell and outer membrane protein (OMP) profiles of strains were examined by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS PAGE), according to the results of the above schemes, to determine the intra-species homogeneity. RESULTS Ninety per cent of strains were identified satisfactorily according to conventional criteria. For these strains, agreement was obtained using the suicide phenomenon and API schemes in 93% and 88% of cases, respectively. The three schemes concurred for 82% of strains. Whole cell protein profiles were unsuitable for comparing strains within a species. However, OMP patterns were similar for 89% of A caviae and 63% of A hydrophila. CONCLUSION Phenospeciation of clinical Aeromonas isolates by the scheme based on the suicide phenomenon is simple to perform and accurate, and suitable for use in the diagnostic laboratory. OMP profiles are potentially useful for confirming the identity of A caviae and most A hydrophila, but not A sobria.