Efficacy of oral immunization with Edwardsiella tarda ghosts against edwardsiellosis in olive flounder (Paralichthys olivaceus)

To investigate whether oral immunization of olive flounder (Paralichthys olivaceus) with Edwardsiella tarda ghosts (ETG) can elicit mucosal and systemic immune responses, and can enhance protection compared to conventional formalin killed bacteria (FKC), fish were fed diets coated with ETG, FKC or PBS alone. Fish immunized with ETG showed significantly higher serum and mucus antibody titers than fish immunized with FKC, which indicate that oral immunization with ETG can elicit both systemic and mucosal adaptive immune responses, and ETG is more favorable to induce specific humoral immune responses in olive flounder than FKC. Furthermore, fish immunized with ETG showed higher survival rates against both immersion and injection challenges than fish immunized with FKC, suggesting ETG has higher potential to induce protective adaptive immunity than FKC.