Evaluation of protective immune response of live-attenuated candidate vaccines ΔcpxA and ΔcpxR against Vibrio alginolyticus in pearl gentian grouper

Abstract

The grouper farming industry was severely influenced by vibriosis. In this study, we developed two live-attenuated vaccine (LAV) candidates against Vibrio alginolyticus infection in pearl gentian groupers using cpxA or cpxR mutant strains of V. alginolyticus (ΔcpxA and ΔcpxR). Groupers were administrated with ΔcpxA and ΔcpxR at the dose of 1.0 × 10⁴ CFU/fish (safety dose) to evaluate the immune protect effect of LAV. The increasing median lethal dose (LD₅₀) of ΔcpxA and ΔcpxR indicated the decreased virulence of bacteria to groupers. Our results suggested that two LAVs achieved over 70 % relative percent survival (RPS) after groupers were challenged by V. alginolyticus on 14 days post-immunization. The immune protection was mainly attributed to the up-regulation of immune-related gene expression (IL-6, IL-12, TNF-α, TLR2, TLR5S, CD4, MHC-Iα, IFN-γ2 and NF-κB), the higher activities of catalase (CAT), lysozyme (LZM), superoxide dismutase (SOD), and the increasing production of total protein (TP) in serum. The research indicated that the vaccination of fish with ΔcpxA and ΔcpxR can induce the innate and acquired immunity and survival rate of groupers after bacterial infection, so they can be considered as the promising candidates of vaccine for grouper industry.