IDENTIFICATION OF ATYPICAL AEROMONAS-SALMONICIDA - INTER-LABORATORY EVALUATION AND HARMONIZATION OF METHODS

The atypical isolates of Aeromonas salmonicida are becoming increasing ly important as the frequency of isolation of bacteria belonging to th is group continues to rise. The primary object of this study was to co mpare and evaluate the results obtained in various laboratories concer ning the biochemical identification of atypical Aer. salmonicida befor e and after standardization of media and methods. Five laboratories ex amined 25 isolates of Aer. salmonicida from diverse fish species and g eographical locations including the reference strains of Aer. salmonic ida subsp, salmonicida (NCMB 1102) and Aer. salmonicida subsp. achromo genes (NCMB 1110), Without standardization of the methods, 100% agreem ent was obtained only for two tests: motility and ornithine decarboxyl ase. The main reason for the discrepancies found was the variation of the incubation time prior to reading the biochemical reactions. After standardization, improvement was obtained with the identification; how ever, disagreement was still observed between the different laboratori es. These findings demonstrate the difficulties involved in a proper i dentification of atypical Aer. salmonicida and also that data presente d in the literature on various strains of Aer. salmonicida are not rea dily comparable. This paper seems to be the first on standardization o f microbiological tests for identification of fish pathogens and the r esults obtained show the need for standardization of methods both with in and between laboratories.