Efficacy of recombinant subunit OMP and hly vaccines against Aeromonas hydrophila in Rohu (Labeo rohita)

The main aim of the current study was to clone and express a new outer membrane protein (OMP) and haemolysin (hly) from a pathogenic Aeromonas hydrophila and to investigate their potential as a vaccine candidate against A. hydrophila infection in Rohu (Labeo rohita). The OMP and hly genes were cloned in pET-30b vector and recombinant plasmids pET-30b-OMP and pET-30b-hly were constructed, which were then transferred into Escherichia coli BL21 (DE3). The recombinant E. coli BL21 (DE3) was induced by IPTG, and the OMP and hly proteins were expressed highly. The proteins OMP and hly were estimated in 15% SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Their molecular weights were found to be 40 kD and 68 kD. The expressed proteins OMP and hly were purified by Ni-NTA His-Bind Resin column, and the immunogenicity was confirmed by Western blotting. The fishes (L. rohita) were divided into IV groups, and the group I fishes were treated with phosphate saline, the II and III group were immunized with the purified OMP and hly recombinant proteins, and the fishes were treated IV group with combined OMP and hly for 10 days. After 10 days of treatment, the fishes of all the four groups were challenged with virulent A. hydrophila. The results revealed that vaccinated fish showed significantly improved haematological profile, phagocytic activity, myeloperoxidase activity and total immunoglobulin levels on the 5th and 10th days. The non-vaccinated group (Group I) showed 100% mortality, whereas the mixture of recombinant OMP (r-OMP) and hly (r-hly) protein-treated groups (Group IV) exhibited higher survival rate (80%). Relatively, expression of pro- and anti-inflammatory cytokines (IL-1β, IL-10 and TGF-β), c-type and g-type lysozymes were significantly up-regulated in heart and kidney of vaccinated groups compared with the non-vaccinated group. Our results revealed that OMP and hly genes were effective vaccine candidates in the aquaculture system and could be used as recombinant subunit vaccine for diseases caused by pathogenic A. hydrophila.