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

Abstract 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 ( rO mpK), outer membrane protein U ( rO mpU) and rO mpK‐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 rO mpK‐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 rO mpK‐OmpU was an effective vaccine candidate that exhibited potentially great versatility for controlling vibrio infections.