Clonality of Vibrio anguillarum strains isolated from fish from the Scandinavian countries, Sweden, Finland and Denmark

In order to investigate whether outbreaks of vibriosis in the Baltic region were caused by the spread of certain pathogenic clones, 291 Vibrio anguill arum isolates from Finland (n = 156), Sweden (n = 88) and Denmark (n = 47) were studied with respect to serogroup, ribotype, plasmid content, and bioc hemical phenotypes as expressed with the PhenePlate (PhP) typing system. Fo r comparison, 54 V. anguillarum serogroup O1 from other countries worldwide were included. Most isolates from Finland, Sweden and Denmark belonged to serogroup O1 (255), followed by O2 (30). Four Finnish isolates cross-reacte d strongly with antisera against two new serogroups VaNT2 and VaNT4, wherea s two strains were non-typeable. The serogroup O1 isolates displayed ten di fferent ribotype patterns, whereas the other strains were considerably more diverse with respect to ribotypes. Most of the O1 isolates carried the 67 kb virulence plasmid and a group of Finnish isolates, in addition, carried an 86 kb plasmid. Additional plasmids with molecular weights of 63, 76, 135 or 260-290 kb were found in single O1 isolates. With few exceptions, strai ns of serogroup O2 either had no plasmids or carried one or two Small plasm ids. PhenePlate typing revealed considerable diversity within the species, serogroup O1 being the most homogeneous. A few PhP types were dominant, whe reas other types were observed only in one to four isolates. The prevalence of the different types changed significantly from one year to another but in Finland, one clonal lineage became increasingly important from 1992 (20% of isolates) to 1996 (80%). Remaining clones were mostly restricted to spe cific geographic areas. By cluster analysis, it was demonstrated that most of the isolates from Finland, Sweden and Denmark belonged to two clusters, and most of the strains from Southern Europe fell into two other, distinct clusters. Most isolates from the UK, North America, Chile and Tasmania grou ped together in a distinct cluster. For the typing of V. anguillarum, O-ser otyping should be the primary method. For isolates belonging to serogroups other than O1, plasmid profiling in combination with ribotyping gives a ver y good discrimination between strains, whereas for serogroup O1, another me thod is required. It is concluded that PhP typing is a tool that provides a good discrimination between O1 isolates.