Identification of fish source Vibrio alginolyticus and evaluation of its bacterial ghosts vaccine immune effects

Vibrio alginolyticus (V. alginolyticus) is a common pathogen for humans and marine aquatic animals. Vibriosis of marine aquatic animals, caused by V.alginolyticus, has become more prevalent globally in recent years. Hence, a safe and effective vaccine is urgently needed for the control of this disease. Here, the strain 16-3 isolated from the large yellow croaker (Larimichthys crocea) suffered from canker was identified as V.alginolyticus based on morphological, biochemical, and 16S rDNA sequencing analysis. Then, recombinant temperature-controlled lysis plasmid pBV220-lysisE was electroporated into the strain 16-3 to generate V.alginolyticus bacterial ghosts (VaBGs) by inducing lysis gene E expression, and the safety and immune effects of VaBGs were further investigated in mice and large yellow croaker. The results showed that VaBGs were as safe as formalin-killed V.alginolyticus cells (FKC) to mice and fish. Compared with FKC and PBS groups, significant elevations of the serum agglutinating antibody titer, serum bactericidal activity, lymphocyte proliferative responses, and levels of four different cytokines (Th1 type: IL-2, TNF-alpha; Th2 type: IL-4 and IL-6) in serum were detected in the VaBGs group, indicating that a Th1/Th2-mediated mixed immune response was elicited by the VaBGs. More importantly, after challenged with the parent strain 16-3, VaBGs-vaccinated mice and fish showed higher protection than FKC-vaccinated mice, the relative percent of survival (RPS) being 60%, 66.7% and 40%, respectively. Taken together, this is the first demonstration that the newly constructed V. alginolyticus ghosts may be developed as a safe and effective vaccine against V. alginolyticus infection in aquaculture.