CHARACTERIZATION OF ISOLATES OF FLAVOBACTERIUM-PSYCHROPHILUM ASSOCIATED WITH COLDWATER DISEASE OR RAINBOW-TROUT FRY SYNDROME I - PHENOTYPICAND GENOMIC STUDIES

Isolates of Flavobacterium psychrophilum (formerly Cytophaga psychroph ila and Flexibacter psychrophilus) mainly originating from clinical ou tbreaks of either coldwater disease (CWD) or rainbow trout fry syndrom e (RTFS) were studied for selected biochemical, physiological, morphol ogical and genomic characteristics, and compared with previously chara cterized French and American strains. DNA hybridization studies showed that the Danish isolates were highly related to the type strain, F. p sychrophilum NCIMB 1947(T). Plasmid profiling of Danish isolates and t hose from other European countries revealed differences, which might b e related to differences in pathogenicity. European isolates originati ng from clinical outbreaks of either RTFS or CND usually harboured one plasmid of 3.2 kb, whereas isolates originating from fish with differ ent or no disease signs had other profiles. Phenotypically, the Danish isolates appeared very homogeneous and shared most characteristics wi th the type strain, and with French and American strains studied by ot her authors. Further studies on the importance of the plasmids and the proteolytic activities of the bacterium might help in elucidating pos sible virulence factors.