An attenuated live strain of HY9901 mutant Δgr provides protection against Vibrio alginolyticus in pearl gentian grouper (♀Epinephelus fuscoguttatus × ♂Epinephelus lanceolatu).

Vibrio alginolyticus is a serious aquaculture bacterial pathogen, which is widely distributed in the ocean and rivers, and cause vibriosis in aquaculture. Therefore, it is imperative to develop effective vaccine to prevent vibriosis. In this study, the efficacy of gr deletion strain (Δgr) of V. alginolyticus as an attenuated live vaccine was evaluated in peal gentian grouper by intraperitoneal injection immunization, followed by a wild strain injection challenge. Real-time fluorescence quantitative PCR was used for analyzing the expression dynamics of immune-related genes. ELISA was used to assess the serum antibody titer and non-specific enzyme activities were determined by kit. The results showed that the safe dose of Δgr was 1.0 × 106 CFU/mL for pearl gentian grouper, and the immune protection rate of Δgr was 73.08 %, providing significant protection against V. alginolyticus. The expression levels of all the immune-related genes MHC-Iα, TNF-α, IL-1β, IL-16 and MyD88 were upregulated in liver, spleen, head kidney and thymus within 42 days post-vaccination. In addition, specific antibody IgM, activities of catalase, superoxide dismutase and lysozyme were also significantly increased compared with the control group. It is not only safe for groupers, but also can effectively stimulate both specific and non-specific immunity of fish. These results indicated that Δgr could be used as an effective attenuated live vaccine candidate to prevent pearl gentian grouper against V. alginolyticus in aquaculture.