Introduction:
Streptococcus agalactiae is a major threat in tilapia aquaculture. This study evaluated the safety and efficacy of a S. agalactiae ghost vaccine (SAGV) formulated with novel adjuvants, Montanide™ GEL 02 (polymer) and Montanide™ ISA 763B VG (emulsion).
Materials and Methods:
For safety, 10 fish/group (~50g) were injected intraperitoneally with 0.2 ml of: PBS (control), SAGV alone (1 x 107 CFU/ml), SAGV with Montanide™ GEL 02, or Montanide™ ISA 763B VG. Fish were observed for one week for adverse effects and necropsied at 4 and 8 weeks post-vaccination to evaluate chronic side effects. For efficacy, 90 fish/group (~ 50g) were injected intraperitoneally with 0.2 ml of the same formulations. Serum bactericidal activity and anti-S. agalactiae IgM titers were measured weekly for two months. Eight weeks post-vaccination, 45 fish/group were challenged with virulent S. agalactiae (1 x 108 CFU/ml). Dead fish were collected daily, and tissues were collected for bacteriological examination to confirm S. agalactiae as the cause of death.
Results:
Safety assessment showed limited oily vaccine residue in the Montanide™ ISA 763B VG group due to the deposit effect inherent to oily adjuvants that allows slow antigen release. No aqueous vaccine residue was observed in the Montanide™ GEL 02 group. Both adjuvants significantly enhanced IgM antibody titers from 2 to 8 weeks post-vaccination (p < 0.01). Montanide™ GEL 02 and Montanide™ ISA 763B VG significantly improved protection against S. agalactiae challenge compared to SAGV alone (p < 0.05), with survival rates of 93.33% and 88.89%, respectively.
Conclusion:
The aqueous adjuvant Montanide™ GEL 02 and the oily adjuvant Montanide™ ISA 763B VG, are safe and effective for injectable S. agalactiae ghost vaccines in tilapia. They enhance both the humoral immune response and protection against bacterial challenge.