First expression and immunogenicity study of a novel trivalent outer membrane protein (OmpII-U-A) from Aeromonas hydrophila, Vibrio vulnificus and Edwardsiella anguillarum

Aeromonas hydrophila, Vibrio vulnificus and Edwardsiella anguillarum are three common bacterial pathogens in cultivated eels. To protect farming eels from infection by these pathogens, a trivalent outer membrane protein (OmpII-U-A) containing partial sequences of OmpII from A. hydrophila, OmpU from V. vulnificus and OmpA from E. anguillarum was expressed as a vaccine to immune European eels (Anguilla anguilla). The expression of 4 immune-related genes, proliferation of whole blood cells, antibody titers in serum and mucus, and activity of SOD were detected at different time after the immunization, and the relative percent of survival (RPS) was determined after eels were infected by A. hydrophila, V. vulnificus or E. anguillarum at 28 d post the immunization (dpi). The results showed that the OmpII-U-A could significantly stimulate the gene expression of sod, mhc2 and lysC post the immunization; SOD activity and the antibody titer in serum and skin mucus were significantly increased. After the challenge on 28 dpi, the RPSs of OmpII-U-A against A. hydrophila, V. vulnificus and E. anguillarum were 66.67%, 44.44% and 22.22%, respectively. The results showed that the OmpII-U-A could protect eel from A. hydrophila and V. vulnificus infection, but had weak protection effect on E. anguillarum in European eels. Expression and immunogenicity of a trivalent Omp were reported for the first time, and results of this study will provide valuable reference for the development of fish multiplex vaccine.