Serogrouping of motile Aeromonas species isolated from healthy and moribund fish

A total of 195 strains of motile Aeromonas isolated from fish were characterized as Aeromonas hydrophila and Aeromonas sobria. In view of the frequency of isolation and the importance of motile Aeromonas species as fish pathogens, a serological classificaton of these organisms was attempted. Antisera were prepared in rabbits against formalinized whole cell suspensions and against boiled cells of 12 different isolates. Seventy-six strains could be grouped by tube agglutination with whole cells as antigen and anti-whole cell antiserum. However, only 39 strains were typable with anti-O serum. Differentiation was made between heat-stable antigens and heat-labile antigens which did not block the O agglutination reaction. The same heat-labile antigen could be associated with different heat-stable particulate antigens, and a relationship was observed between the heat-stable particulate antigens and the virulence of A. hydrophila for fish. In addition to these two types of antigen, motile Aeromonas possessed heat-stable soluble antigens which could be detected by indirect hemagglutination. One strain seemed to possess various heat-stable soluble antigens; so far, however, it does not appear to be feasible to use these antigens for serology. Finally, we also observed cross-reactions between some A. hydrophila and A. sobria strains.