Protective Efficacy of Formalin-killed Serotype I and II Vaccines for Streptococcus parauberis Infection in Japanese Flounder Paralichthys olivaceus

Abstract

Japanese flounder Paralichthys olivaceus were immunized intraperitoneally with formalin-killed cells (FKC) prepared from serotype I or II of Streptococcus parauberis.　Three weeks after immunization, the fish were challenged with the homologous or heterologous serotype by subcutaneous or intravascular injection. Both serotype FKCs proved to be effective against the challenges with the homologous isolate [relative percent survival (RPS) values: 100%], whereas RPS values in the fish challenged with the heterologous serotype isolates varied from 0% to 100%. These results suggested that each serotype FKC has insufficient cross-protective efficacy against the other serotype.