DAO 31:197-208 (1997)  -  doi:10.3354/dao031197

Characterization of isolates of Flavobacterium psychrophilum associated with coldwater disease or rainbow trout fry syndrome I: phenotypic and genomic studies

Ellen Lorenzen1,*, Inger Dalsgaard2, Jean-Francois Bernardet3

1Danish Veterinary Laboratory, Hangøvej 2, DK-8200 Århus N, Denmark
2Danish Institute for Fisheries Research, Fish Disease Laboratory, Royal Veterinary and Agricultural University, Bülowsvej 13, DK-1870 Frederiksberg C, Denmark
3Laboratoire de Virologie et d'Immunologie Moléculaires, Centre de Recherches INRA, F-78352 Jouy-en-Josas cedex, France
*E-mail:

Isolates of Flavobacterium psychrophilum (formerly Cytophaga psychrophila and Flexibacter psychrophilus) mainly originating from clinical outbreaks of either coldwater disease (CWD) or rainbow trout fry syndrome (RTFS) were studied for selected biochemical, physiological, morphological and genomic characteristics, and compared with previously characterized French and American strains. DNA hybridization studies showed that the Danish isolates were highly related to the type strain, F. psychrophilum NCIMB 1947T. Plasmid profiling of Danish isolates and those from other European countries revealed differences, which might be related to differences in pathogenicity. European isolates originating from clinical outbreaks of either RTFS or CWD usually harboured one plasmid of 3.2 kb, whereas isolates originating from fish with different or no disease signs had other profiles. Phenotypically, the Danish isolates appeared very homogeneous and shared most characteristics with the type strain, and with French and American strains studied by other authors. Further studies on the importance of the plasmids and the proteolytic activities of the bacterium might help in elucidating possible virulence factors.


Flavobacterium psychrophilum · Coldwater disease · Rainbow trout fry syndrome · Phenotype · Haemagglutination · DNA-DNA hybridization · Plasmids


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