Protection of red snapper (Lutjanus sanguineus) against Vibrio alginolyticus with a DNA vaccine containing flagellin flaA gene

Aims: The main aims of this study were to construct a DNA vaccine containing flagellin flaA gene from Vibrio alginolyticus strain HY9901 and to explore the potential application of pcDNA-flaA as a DNA vaccine candidate for red snapper (Lutjanus sanguineus). Methods and Results: Plasmid DNA encoding flagellin flaA gene (designated as pcDNA-flaA) was used as a DNA vaccine to immunize red snapper. The distribution, expression and immunoprotection of the DNA vaccine were analysed in tissues of the red snapper by PCR, RT-PCR and challenge test. PCR results indicated that pcDNA-flaA distributed in liver, spleen, kidney, gill and injection site muscle at 7-28 days after vaccination. RT-PCR results indicated that the flaA gene was expressed in all above tissues of vaccinated fish at 7-28 days after vaccination. In addition, fish receiving the DNA vaccine developed a protective response to live V. alginolyticus challenge 28 days post inoculation, the relative per cent survival (RPS) was 88%. Conclusions: This study showed that injection of pcDNA-flaA induced an efficient, systemic and antigen-specific immune response in red snapper, which makes it an effective vaccine candidate against V. alginolyticus infection. Significance and Impact of the Study: The finding that red snapper does adequately respond to pcDNA-flaA intramuscular injection makes pcDNA-flaA a promising candidate for DNA vaccine treatment. Furthermore, the availability of red snapper for foreign gene expression represents a useful model to develop effective prophylactic strategies and opens new perspectives for the treatment of bacterial pathogens of marine cultured fish.