Streptococcosis in Oreochromis sp.: is feed-based biofilm vaccine of Streptococcus agalactiae effective?

This study was carried out to determine the potential of a biofilm vaccine of Streptococcus agalactiae in protecting tilapia from streptococcocal infection. The tilapia were vaccinated orally using the biofilm vaccine with 10(9)10(10) CFU/g (FBV) incorporated in feed and killed whole-cell vaccine (FCV) of S. agalactiae also prepared in feed, and the unvaccinated control group (Cx) was fed with standard feed formulation. Throughout the study, serum, mucus and gut lavage fluid were collected to evaluate the antibody responses among the groups. The results showed that tilapia vaccinated with FBV exhibited significantly (p < 0.05) stronger immune response and high protection with the relative percentage survival (RPS) of more than 70% (85%) compared with the FCV group, which was only 56%. None of the tilapia in the Cx group survived (0%) post-challenge. Thus, the study revealed that the feed-based biofilm vaccine (FBV) significantly confers the immune protection against the high-dose challenge of S. agalactiae by secretion of the protective immunity in the mucosal and humoral in tilapia.