A recombinant truncated surface immunogenic protein (tSip) plus adjuvant FIA confers active protection against Group B streptococcus infection in tilapia.

Tilapia is an important agricultural fish that has been plagued by Group B streptococcus (GBS) infections in recent years, some of them severe. It is well-known that surface immunogenicity protein (Sip) is an effective vaccine against GBS. Since Sip was not expressed in either E. coli BL21 or E. coli Rosetta, we removed the N-terminal signal peptide and LysM of the virus to produce purified truncated Sip (tSip(1)), which multiplied easily in an E. coli host. The antibody's ability to recognize and combine with GBS was determined by Western-blot and specific staining in vitro. The relative percentage of survival (RPS), antibody titers, bacterial recovery, and pathologic morphology were monitored in vivo to evaluate the immune effects. Freund's incomplete adjuvant (FIA) plus tSip and aluminum hydroxide gel (AH) plus tSip were also evaluated. It revealed that tSip mixed with FIA was an effective vaccine against GBS in tilapia, while AH is toxic to tilapia.