Construction and Analysis of the Immune Effects of a Streptococcus agalactiae Surface Protein ScpB Vaccine Encapsulated with Polylactic-Co-Glycolic Acid (PLGA)

In order to find an effective immune preparation to control tilapia streptococcus disease, the Streptococcus agalactiae surface protein serine protease C5a peptidase (ScpB) was cloned and the recombinant protein was encapsulated in poly (lactide-co-glycolic acid) (PLGA) microspheres, which were comprised of biodegradable materials. The ScpB-PLGA vaccine was then administered to the tilapia intraperitoneally at different concentrations, with PBS used as a control, and the relative percent survival (RPS) of each group was calculated. Serum lysozyme and superoxide dismutase (SOD) activity levels and antibody levels (OD450nm) were tested weekly for the duration of the experiment. The results showed that the ScpB loading rate in the PLGA microspheres was 2.55% and the encapsulation efficiency reached 48.76%. The RPS ranged from 66.80% to 87.66%, with the highest RPS noted in group P1 (1 μg/g). The serum lysozyme, SOD and antibody (IgM) levels were significantly higher in the vaccinated fish relative to the control groups (P < 0.01). These results showed that PLGA could serve as an effective adjuvant for a ScpB vaccine and could provide relatively sustained immune protection.