Serotyping of Aeromonas Species Isolated from Polish Fish Farms in Relation to Species and Virulence Phenotype of the Bacteria

The aim of the study was to determine the relationship between serogroups, species, and virulence of Aeromonas sp. Isolates from common carp and rainbow trout were tested for species designation and virulence phenotype and then serogrouped. A total of 558 isolates were tested. The bacteria were identified to species level using PCR-RFLP method. The β-haemolysin, gelatinase, and caseinase activities were selected for virulence determination. The following species were dominant: A. hydrophila (35), A. bestiarum (103), A. salmonicida (98), A. sobria (101), A. veronii bt. sobria (171), and A. encheleia (30). 380 isolates were classified as virulent for fish. The isolates were serogrouped by agglutination tests according to the scheme of Sakazaki and Shimada. 478 isolates were serologically typeable (they did not show R type antigen or autoagglutination) and for 419 (87.6%) O-antigen was identified. The dominant serogroups among both carp and trout isolates were: O:11, O:16, O:18, O:33, PGO1, and PGO2. Groups O:3, O:6 O:41, PGO4, and PGO6 dominated among carp isolates and groups O:21, O:29, PGO5, and PGO9 were only represented by trout isolates. The relationship between Aeromonas serogroups and species was not found. Of the 15 dominant serogroups, eight groups included only isolates with virulence phenotype and two groups included only non-pathogenic isolates. The remaining groups were represented by virulent, as well as non-virulent isolates. Agglutination test can be used as alternative or complementary method to differentiate pathogenic and non-pathogenic isolates from carp and trout cultured in Poland.