CLASSIFICATION OF FISH-PATHOGENIC VIBRIOS BASED ON COMPARATIVE 16S RIBOSOMAL-RNA ANALYSIS

No systematic classification of fish-pathogenic vibrios has been accom plished previously despite the use of serological, physiological, and genetical classification systems. In this study, a comparative 16S rRN A analysis of 34 strains (representing seven species) of fish-pathogen ic vibrios was performed, The 16S rRNA sequences were obtained by usin g; reverse transcriptase, Nearly complete sequences were obtained for nine strains, On the basis of the results of this analysis, the remain ing strains were investigated by analyzing selected stretches containi ng a total of 560 nucleotides. With the exception of a few strains, in cluding ATCC 43313 (serovar 09), our comparative 16S rRNA analysis con firmed that strains preliminarily identified as Vibrio anguillarum wer e phylogenetically closely related, Strains of V, anguillarum could be divided into groups, with the main group containing serotype 01 and 0 2 strains isolated from Atlantic salmon, rainbow trout, turbot, cod, a nd saithe, The other distinctive group was represented by type strain NCMB 6, This strain was nearly indistinguishable from the type strains of Vibrio ordalii and Vibrio damsela on the basis of the 16S rRNA str etches compared. The results of a comparative 16S rRNA analysis justif ied the status of Vibrio salmonicida as a distinct species. Originally , this species was characterized biochemically as a very homogeneous s pecies, However, two strains, which were isolated from diseased halibu t and from the intestines of healthy cod, could not be distinguished f rom V. salmonicida strains phylogenetically, although they differed fr om the original species description in several phenotypic traits, Our results indicate that V, salmonicida and Vibrio fischeri form a cluste r that is clearly separated from the cluster that includes V. anguilla rum.