Immunoprotective efficacy of Escherichia coli-derived outer membrane vesicles displaying PlpE protein of Pasteurella multocida

Pasteurella multocida (P. multocida), a pathogenic bacterium known to induce duck cholera, stands as a significant contributor to bacterial diseases afflicting the duck industry, causing substantial annual economic losses on a global scale. In this study, the genes encoding the lipoproteins PlpE of P. multocida strain PMWSG-4 was cloned, inserted into the pBAD-ClyA vector, and the recombinant outer membrane vesicles (OMVs) fused with PlpE antigen of P. multocida was expressed by Escherichia coli (E. coli). Ducks immunized with OMV-PlpE had significantly (P < 0.001) increased production of antigen-specific antibodies. Moreover, at 28 days post-immunization, the expression of genes associated with immune response, including interleukin (IL)-2, IL-4, IL-10, and interferon (IFN)-γ in the spleen tissue of immunized ducks were significantly (P < 0.001) up-regulated compared to unimmunized ducks in the control group. And the active serum had significant bactericidal effects against the PMWSG-4 strain (P < 0.001). The protective efficacy of the vaccines was evaluated by leg muscle challenge with 20 LD50 doses of P. multocida, with the recombinant OMV-PlpE conferring 100 % protection. Histopathological examination and tissue bacterial load detection revealed that OMV-PlpE mitigated tissue damage and bacterial colonization to a statistically significant extent (P < 0.001). These findings serve as a valuable reference for the development of vaccines against P. multocida.