MOLECULAR AND PHENOTYPIC METHODS FOR THE CHARACTERIZATION OF ATYPICALAEROMONAS-SALMONICIDA

Atypical Aeromonas salmonicida form a taxonomically diverse group amon g the psychrophilic A. salmonicida. Characteristics of 53 atypical A. salmonicida strains originating from Finland, Denmark, Norway and Swed en were studied using 60 phenotypic tests, Ribopattern analysis and pl asmid profiles were used as genetic methods. The production of brown p igment on the furunculosis agar containing L-tyrosine divided the atyp ical oxidase-positive strains into two groups: pigment-producing (n = 35) and achromogenic (n = 16), PstI differentiated all the atypical A, salmonicida from A, salmonicida subsp. salmonicida. Combined ribopatt erns ClaI/PstI divided pigment producing atypical strains into four ma jor groups B/B, G/G, G/T, F/F. Most of the achromogenic oxidase-positi ve strains belonged to two major groups H/H or U/U, Cluster analysis o f ribopatterns and plasmid profile analysis also supported the divisio n of atypical oxidase-positive A. salmonicida into pigment-producing a nd achromogenic groups. The oxidase-negative strains formed a distinct group which differed from oxidase-positive atypical A. salmonicida ty pe biochemically and in terms of ribopatterns. Our results also suppor t the use of ribopattern analysis as a valid method to study the epide miology of infections caused by atypical A. salmonicida on fish farms. (C) 1997 Elsevier Science B.V.