A novel multivalent vaccine based on secretary antigen-delivery induces protective immunity against Vibrio anguillarum and Aeromonas hydrophila.

In our previous work, four secretory antigen-delivery systems based on different signal peptides (SPs) (SP(hlyA), SP(rtxA), SP(vah3) and SP(empA)) have been successfully established in attenuated Vibrio anguillarum. To investigate the potential application of the antigen-delivery systems in V. anguillarum multivalent vector vaccine, the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from pathogenic Aeromonas hydrophila, as a putative protective antigen, was fused to the four delivery systems, respectively, and introduced into attenuated V. anguillarum strain MVAV6203 to get four GAPDH-delivery strains in this work. Immunodetection of GAPDH indicated that among the four constructs, the SP(empA)-mediated GAPDH-delivery strain AV(pGap-empA) showed the highest level of GAPDH expression and secretion, and was determined as the multivalent vaccine candidate. Further immune protection evaluation of AV(pGap-empA) in turbot (Scophtalmus maximus) demonstrated that the vaccine candidate could induce efficient protection against V. anguillarum and A. hydrophila, suggesting that this vector vaccine had great potential in serving as a valuable multivalent live vaccine.