Since 2009, Aeromonas hydrophila has emerged as a primary pathogen impacting U.S. catfish aquaculture, causing Motile Aeromonas Septicemia (MAS). The disease has led to severe economic losses, with mortality rates often exceeding 90% in affected ponds and rapid spread across farms. Current therapeutic and preventative strategies against vAh remain limited, highlighting the need for improved solutions.
Our group demonstrated that recombinant vAh surface proteins (OmpA1, Tdr, Fim, FimA, FimMrfG, and an ATPase) significantly protect catfish against MAS. Additionally, the live attenuated Edwardsiella ictaluri vaccine strain ESC-NDKL1 is an effective vaccine for ESC and serves as a vector for expressing vAh antigens. Based on this, 18 recombinant ESC-NDKL1 strains expressing one or two vAh surface antigens were developed, with strains expressing two antigens providing enhanced protection compared to those expressing one.
The study aimed to enhance the vaccine efficacy of recombinant ESC-NDKL1 strains expressing two vAh antigens. Eleven recombinant ESC-NDKL1 strains expressing three vAh antigens were constructed by in-frame insertion of a vAh antigens into the chromosome of recombinant ESC-NDKL1 strains expressing two vAh antigens and tested on channel catfish fingerlings. Four strains (ESC-NDKL1::fimMrfG::ompA::fimA, ESC-NDKL1::atpase::fimMrfG::ompA, ESC-NDKL1::fim::fimMrfG::ompA, and ESC-NDKL1::atpase::tdr::fim) provided the best protection, with relative percent survival (RPS) ranging from 63.18% to 82.35%. Additionally, the triple recombinant strains induced a stronger antibody response compared to double and single recombinant strains, demonstrating improved vaccine efficacy.