Antigenic and molecular characterization of Vibrio ordalii strains isolated from Atlantic salmon Salmo salar in Chile.

Biochemical, serological and molecular properties of a group of 14 Vibrio ordalii strains isolated from cultured Atlantic salmon Salmo salar in Chile in recent years were studied. The charac- teristics of isolates were compared with the type strain V. ordalii ATCC 33509 T. The Chilean V. ordalii represented a biochemically homogenous group; however, some minor differences with the type strain were observed. The serological relationships among isolates, as well as the study of their anti- genic determinant (LPS) revealed a strong reaction with antisera raised against Atlantic salmon strains and the antiserum raised against Listonella anguillarum serotype O2. However, LPS elec- trophoretic patterns were completely different from the V. ordalii type strain, regardless of the serum employed, suggesting the possibility that the Chilean strains constitute a new serological subgroup within this bacterial species. Genetic analyses by PFGE, RAPD, REP-PCR and ERIC-PCR demon- strated that all V. ordalii strains were genetically homogenous, displaying similar DNA patterns, regardless of the techniques used. Moreover, the analysis of DNA banding patterns generated by ERIC-PCR and REP-PCR also clearly separated the type strain from the Chilean strains. This is the first report of characterization of V. ordalii strains from the Southeastern Pacific area, the results of which should facilitate the development of vaccines for protecting cultured Atlantic salmon against vibriosis in this area.