Immunogenicity of the LrrG protein encapsulated in PLGA microparticles in Nile tilapia (Oreochromis niloticus) vaccinated against Streptococcus agalactiae

Abstract

LrrG protein is one of the conserved surface proteins of Streptococcus agalactiae. It has been found exists in all kinds serotypes of S. agalactiae strains. Preliminary experimentation showed that LrrG protein of S. agalactiae isolated from tilapia protected tilapia from S. agalactiae infection. In order to investigate the immune protective effects of LrrG protein of S. agalactiae encapsulated by poly-(d, l-lactic-co-glycolic) acid (PLGA) on tilapia, PLGA microparticles containing LrrG protein were prepared by double emulsion-solvent evaporation. The average diameter of PLGA-LrrG protein microparticle was 4.5μm, the encapsulation efficiency was 38.54%, the drug loading was 1.98%, and the cumulative rate of drug-release over 28days was 78.97%. Healthy tilapias were immunized with PLGA-LrrG microparticles by intraperitoneal injection or oral administration. The results show that the relative percent survival (RPS) of vaccinated groups from both intraperitoneal injection and oral administration were significantly higher than that of the control groups. Although in the same dose group, the RPS from intraperitoneal injection was generally higher than that from oral administration, one microgram per gram (1μg/g) PLGA-LrrG microparticle also showed good immune protection and RPS (77.54%) in oral administration. These results suggest that PLGA-LrrG microparticles can be used to protect tilapia from S. agalactiae infection and it may have practical value as an orally administered genetically engineered vaccine against streptococcosis in tilapia.