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 Montanide^TM 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.