Recombinant cell
vaccines expressing the OmpK and DnaJ of Vibrio 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 107 CFU/mL of the inactivated recombinant cells
vaccines, the pET-32/LIC-OmpK and pET-32/LIC-DnaJ, respectively. Group 3 was similarly injected with 107 CFU/mL of inactivated E. coli BL21 (DE3), Group 4 with 107 CFU/mL of
formalin killed whole cells V. harveyi, and Group 5 with PBS
solution. Serum, mucus, and gut lavage were used to determine the antibody levels before all fish were challenged with V. harveyi, V. alginolyticus, and V. parahemolyticus, respectively on day 15 post-vaccination. There was significant increase in the serum and gut lavage antibody titers in the juvenile seabass vaccinated with r-OmpK
vaccine. In addition, there was an up-regulation for TLR2, MyD88, and MHCI genes in the kidney and intestinal tissues of r-OmpK vaccinated fish. At the same time, r-OmpK triggered higher expression level of
interleukin IL-10,
IL-8, IL-1ß in the spleen, intestine, and kidney compared to r-DnaJ. Overall, r-OmpK and r-DnaJ triggered protection by curbing
inflammation and strengthening the adaptive immune response. Vaccinated fish also demonstrated strong cross protection against heterologous of Vibrio isolates, the V. harveyi, V. alginolyticus, and V. parahaemolyticus. The fish vaccinated with r-OmpK
protein were completely protected with a relative per cent of survival (RPS) of 90 percent against V. harveyi and 100 percent against V. alginolyticus and V. parahaemolyticus. A semi-quantitative PCR detection of Vibrio spp. from the seawater containing the seabass also revealed that vaccination resulted in reduction of pathogen shedding. In conclusion, our results suggest r-OmpK as a candidate
vaccine molecule against multiple Vibrio strain to prevent
vibriosis in marine fish.