VIBRIO-ANGUILLARUM SEROGROUP O3 AND V-ANGUILLARUM-LIKE SEROGROUP O3 CROSS-REACTIVE SPECIES - COMPARISON AND CHARACTERIZATION

Forty-five Vibrio anguillarum-like isolates reacting with V. anguillar um serogroup O3 antiserum were examined in 30 characters to clarify th eir phenotypical properties, while their genotype was examined by ribo typing. The strains were isolated from diseased and dead fish or from environmental sources such as water, sediment, plankton, and faeces an d gills of healthy fish. Phenotypically, the similarity of all the str ains was more than 90%. However, significant differences between the f ish-associated and environmental strains were detected, Biochemically, deviations were found in the Voges-Proskauer test and lysine decarbox ylase reaction. Clustering analysis of the ribotypes showed two distin ct clusters with a similarity of only 32%. Two strains representing ea ch of these groups were used in a LD(50) study, which showed some diff erence also in the pathogenicity between environmental and fish strain s. It is suggested that the environmental strains belong to another sp ecies than V. anguillarum, but serologically cross-reacting with the V . anguillarum serogroup O3. The ribotyping as well as biochemical resu lts indicated that the environmental strains possibly belong to Vibrio aestuarianus. The bona fide V. anguillarum serogroup O3 strains prove d to be very homogeneous both phenotypically and genotypically, and th e similarity of ribotypes was more than 96%. The V. anguillarum-like, serogroup O3-reactive strains from the environment were more heterogen eous in their biochemical behaviour,and showed an approximately 70% si milarity in ribotypes.