Development of a recombinant live attenuated vaccine to protect channel catfish against motile Aeromonas septicemia

Background/objectives Aeromonas hydrophila causes motile Aeromonas septicemia (MAS), which affects farm-raised catfish. Since 2009, outbreaks caused by a clonal genetic group of A. hydrophila (virulent A. hydrophila , or vAh) have caused significant losses of market-size catfish in Alabama and Mississippi. Previously, our group reported that recombinant vAh surface proteins are effective in protecting catfish against MAS. Furthermore, live attenuated Edwardsiella ictaluri vaccine strain ESC-NDKL1 is an efficacious vaccine for enteric septicemia of catfish (ESC). In the current study, we investigated ESC-NDKL1 as a potential vector for expressing vAh antigens. Methods and results Genes encoding vAh surface antigens were integrated into the ESC-NDKL1 chromosome by conjugation and homologous recombination. Six recombinant ESC-NDKL1 strains expressing one vAh antigen (ESC-NDKL1:: atpase , ESC-NDKL1:: fim , ESC-NDKL1:: fimMrfG , ESC-NDKL1:: fimA , ESC-NDKL1 ::tdr , and ESC-NDKL1:: ompA ) showed significant protection against MAS with relative percent survival (RPS) of 52.10%, 25.67%, 39.99%, 38.93%, 47.83%, and 34.07%, respectively. Eleven recombinant ESC-NDKL1 strains expressing two vAh antigens showed significant protection against MAS and improved protection compared to recombinant ESC-NDKL1 strains expressing one vAh antigen. In particular, four recombinant ESC-NDKL1 strains expressing two vAh antigens (ESC-NDKL1:: atpase :: fimMrfG , ESC-NDKL1:: fim :: fimMrfG , ESC-NDKL1:: tdr ::f imMrfG , and ESC-NDKL1:: fim :: ompA) showed significant protection ( p < 0.05) compared to non-recombinant ESC-NDKL1 with RPS of 55.72%, 60.18%, 61.74%, and 54.81%, respectively. Conclusion We identified four promising vaccine candidate strains to control MAS in the catfish industry.