Random amplified polymorphic DNA analysis provides rapid differentiation among isolates of the fish pathogen Flavobacterium psychrophilum and among Flavobacterium species

Flavobacterium psychrophilum is the agent of cold-water disease and rainbow trout fry syndrome in salmonid fish. Originally isolated in North America only, the bacterium is now also responsible for severe mortalities in many salmonid hatcheries in Europe, as well as in Japan, Chile and Tasmania. The random amplified polymorphic DNA (RAPD) technique was used to analyze the genetic diversity among a collection of 177 F. psychrophilum strains isolated from different fish species and in different geographical areas. Forty 10-mer primers were tested and 5 of them were selected for further analysis of the bacterial DNAs. The primers OPH 06, OPH 08, OPG 08, OPG 14, and OPG 16 generated several reproducible profiles during a preliminary screening of the whole collection of strains. Based on these results, the polymerase chain reaction (PCR) products of a selection of 60 bacterial DNAs were submitted to slow agarose gel electrophoresis for numerical analysis of the DNA fingerprintings. No correlation occurred between the combined RAPD profiles of the primers and the geographical origin of the strains, while some profiles were clearly associated with the fish species from which the strains were isolated. Another primer, OPG 10, yielded a unique RAPD profile common to all F. psychrophilum strains whereas the 9 other valid Flavobacterium species, several of which coexist in freshwater environments and may also be isolated from fish, displayed other profiles. Thus, depending on the primer used, both the typing of F, psychrophilum strains for epidemiology studies as well as the identification of this fish pathogen and its differentiation from related bacterial species could be achieved by using RAPD.