Enhanced immune responses and effectiveness of refined outer membrane protein vaccines against Vibrio harveyi in orange-spotted grouper (Epinephelus coioides).

Vibriosis is a severe infection occurring in many commercially important marine fish species. In this study, vaccines containing Vibrio harveyi recombinant outer membrane protein K (rOmpK), outer membrane protein U (rOmpU) and rOmpK-OmpU fusion protein in addition to the metabolizable MontanideTM ISA 763 A VG adjuvant were developed and evaluated in the orange-spotted grouper. The results indicate that recombinant V. harveyi protein-based vaccines resulted in a remarkably higher expression of IL-1β and IL-8 at 24 hr, and greater antibody production, as early as 2 weeks postimmunization. Notably, enhanced immune responses and significant protective efficacy against V. harveyi infections were observed in the fusion protein vaccine-injected fishes with relative per cent survival value of 81.8%. Additionally, the rOmpK-OmpU antisera presented a high bactericidal effect on not only V. harveyi, but also Vibrio parahaermolyticus and Vibrio alginolyticus. Our results demonstrated that the fusion protein rOmpK-OmpU was an effective vaccine candidate that exhibited potentially great versatility for controlling vibrio infections.