Elucidating the Efficacy of Vaccination against Vibriosis in Lates calcarifer Using Two Recombinant Protein Vaccines Containing the Outer Membrane Protein K (r-OmpK) of Vibrio alginolyticus and the DNA Chaperone J (r-DnaJ) of Vibrio harveyi

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