A Comparative Study on the Properties and Pathogenicities of β-Hemolytic Streptococcus sp. Isolated from Marine and Freshwater Fishes

Abstract

A comparative taxonomical studies were performed between 14 β-hemolytic Streptococcus strains isolated from diseased cultured yellowtail, Seriola quinqueradiata, Japanese flounder, Paralichthys olivaceus, ayu, Plecoglossus altivelis, and natural common mackerel, Scomber japonicas and strains of S. iniae and S. equisimilis. The phenotypic characteristics of the fish isolates agreed well with each other, and were identical to those of S. iniae ATCC 29178. According to the result obtained from slide agglutination tests, the surface antigens of these fish isolates were found to be homologous. However, serotypes of these fish isolates were different from that of S. iniae ATCC 29178. From the results of experimental infection tests against yellowtail and ayu, it was observed that all the strains isolated from cultured marine and freshwater fish, and natural fish possessed the same pathogenicity. The results of the present study suggest that the distribution of β hemolytic Streptococcus in marine and freshwater environment is ubiquitous and they are the same strains as S. iniae.