Construction and Evaluation of Recombinant Lactococcus lactis Expressing the vscO Gene as a Safe Live Oral Vaccine against Vibrio alginolyticus

Vibrio alginolyticus is responsible for significant economic losses in the fish industry. It is urgent to develop a vaccine against V. alginolyticus. In this study, a recombinant Lactococcus lactis expressing the VscO protein of V. alginolyticus (Lc-pMG36e-vscO) is constructed. The Lc-pMG36e-vscO has good hereditary stability. The immune responses in pearl gentian grouper (Epinephelus fuscoguttatus (♀) × E. lanceolatu (♂)) vaccinated with Lc-pMG36e-vscO are evaluated. The titers of specific antibody in the immunized grouper displayed an upward and then downward tendency during the total experiments and reached the peak value of 9.6 at the fourth week after booster immunization. The expression levels of IL-1β, IL-16, TNF-α, and MHC-1α gene in the Lc-pMG36e-vscO group were significantly upregulated after vaccination, indicating that the Lc-pMG36e-vscO could induce an effective and durable immune response. In vivo challenge of the Lc-pMG36e-vscO-immunized fish with V. alginolyticus showed a relative survival percentage of 68%. These results indicated that Lc-pMG36e-vscO could be promising as a candidate oral vaccine against V. alginolyticus.