PHENOTYPIC AND MOLECULAR CHARACTERISTICS OF AEROMONAS-SALMONICIDA SUBSP SALMONICIDA ISOLATED IN SOUTHERN AND NORTHERN FINLAND

Aeromonas salmonicida subsp. salmonicida causes outbreaks of furunculo sis in salmonid fish. Furunculosis was first detected in Finland in 19 86 on fish farms located on the Finnish coast of the Bothnian Bay. Mol ecular methods, SDS-PAGE, ribotyping, randomly amplified polymorphic D NA (RAPD) and plasmid profile analysis as well as phenotypic character istics (biochemical characteristics, maximum growth temperature, pigme nt and elastase production) were used both for typing the strains and to study the possible routes of transmission of the organism to Finlan d and the spread of infection within Finland from 1986 to 1993. Ribopa ttern analysis of chromosomal DNA digested with SmaI, Bg/I, PstI and C LI of 28 Finnish strains and eight foreign strains (Denmark, Sweden, N orway or Canada) showed that ail Finnish strains and the Swedish strai n originating from the Swedish coast of the Bothnian Bay had identical ribopatterns. All other foreign strains had distinct, unique ribotype s except for the second Swedish strain studied, the ribotype of which was identical with that of one Danish strain. RAPD typing, based on th e results of two arbitrary primers, yielded 15 types for the Finnish s trains, Except for both Danish strains, which had the RAPD type which was identical with that of one Finnish strain, the foreign strains had RAPD patterns differing from those of the Finnish strains. Plasmid pr ofile typing and RAPD profile typing did not correlate. Ribotyping wit h four different enzymes proved to be the most sensitive method for st udying genetically homogeneous Aer. salmonicida subsp. salmonicida. Ri bopattern analysis showed that the infection which first started in 19 84/1985 on the Swedish coast of the Bothnian Bay may have been transmi tted to Finland where the first outbreaks occurred in 1986. The strain s infecting Finnish fish farms were very homogeneous, with most differ ences seen, for example, in maximum growth temperature, plasmid profil es and the RAPD profiles of the strains.