Abstract

The biochemical, serological and molecular characteristics of 8-pigmented isolates phenotypically related to Flavobacterium psychrophilum were determined. The bacteria were isolated in 2006 from diseased Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) cultured in the South of Chile. The F. psychrophilum type strain ATCC 49418T and isolate B97026, obtained from rainbow trout in UK, were included in the study as a comparison. Their potential to cause pathology in Atlantic salmon was also investigated. The 8 isolates were biochemically identical, however were completely different to F. psychrophilum. Slide agglutination and Dot blot allowed us to confirm that the isolates constituted a homogeneous, but distinctive serological group to the F. psychrophilum isolates. Similar homogeneity was observed using RAPD-PCR with identical DNA patterns obtained, regardless of the source of isolation or geographic origin. Therefore, any of the above tests can be used to discriminate these pigmented bacteria from F. psychrophilum. Virulence studies suggest that these isolates could be considered as a potential pathogen for salmonids, mainly in mixed cultures with F. psychrophilum. These fish showed typical signs of flavobacteriosis. Recent studies on the sequencing of the 16S rRNA gene, together with the phenotypic and biochemical properties obtained in this study permitted us classify these 8 isolates in the genus Chryseobacterium. Further molecular studies are in progress in order to know the species of these pigmented bacteria and determine the real risk for the salmonid culture.