| Summary: | Recombinant cell vaccines expressing the <i>OmpK</i> and <i>DnaJ</i> of <i>Vibrio</i> were developed and subsequently, a vaccination efficacy trial was carried out on juvenile seabass (~5 cm; ~20 g). The fish were divided into 5 groups of 50 fish per group, kept in triplicate. Groups 1 and 2 were injected with 10<sup>7</sup> CFU/mL of the inactivated recombinant cells vaccines, the pET-32/LIC-<i>OmpK</i> and pET-32/LIC-<i>DnaJ</i>, respectively. Group 3 was similarly injected with 10<sup>7</sup> CFU/mL of inactivated <i>E. coli</i> BL21 (DE3), Group 4 with 10<sup>7</sup> CFU/mL of formalin killed whole cells <i>V. harveyi</i>, and Group 5 with PBS solution. Serum, mucus, and gut lavage were used to determine the antibody levels before all fish were challenged with <i>V. harveyi</i>, <i>V. alginolyticus</i>, and <i>V. parahemolyticus</i>, respectively on day 15 post-vaccination. There was significant increase in the serum and gut lavage antibody titers in the juvenile seabass vaccinated with <i>r</i>-<i>OmpK</i> vaccine. In addition, there was an up-regulation for TLR2, MyD88, and MHCI genes in the kidney and intestinal tissues of <i>r-OmpK</i> vaccinated fish. At the same time, <i>r-OmpK</i> triggered higher expression level of interleukin IL-10, IL-8, IL-1ß in the spleen, intestine, and kidney compared to <i>r-DnaJ</i>. Overall, <i>r-OmpK</i> and <i>r-DnaJ</i> triggered protection by curbing inflammation and strengthening the adaptive immune response. Vaccinated fish also demonstrated strong cross protection against heterologous of <i>Vibrio</i> isolates, the <i>V. harveyi</i>, <i>V. alginolyticus</i>, and <i>V. parahaemolyticus</i>. The fish vaccinated with <i>r-OmpK</i> protein were completely protected with a relative per cent of survival (RPS) of 90 percent against <i>V. harveyi</i> and 100 percent against <i>V. alginolyticus</i> and <i>V. parahaemolyticus</i>. A semi-quantitative PCR detection of <i>Vibrio</i> spp. from the seawater containing the seabass also revealed that vaccination resulted in reduction of pathogen shedding. In conclusion, our results suggest <i>r-OmpK</i> as a candidate vaccine molecule against multiple <i>Vibrio</i> strain to prevent vibriosis in marine fish.
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