The isolation and immunoprotective efficacy of outer membrane vesicles of Dichelobacter nodosus

Dichelobacter nodosus is a major causative agent of infectious foot diseases in ruminants, responsible for substantial economic losses globally in the livestock industry. The development of a vaccine is therefore of great importance. In this study, we employed density gradient ultracentrifugation to extract outer membrane vesicles (OMVs) from D. nodosus and evaluated their immunoprotective effects. The extracted OMVs were spherical structures with an average diameter of 144 nm, predominantly comprising outer membrane proteins, toxin proteins, and lipoproteins, mainly involved in biological processes such as cellular protein metabolism and protein transmembrane transport. Mice immunized with OMVs showed significantly increased production of serum antigen-specific antibodies (P < 0.0001). In addition, compared with the control group, the expression of tumor necrosis factor-α, interferon-γ, and interleukin-1 in the serum of mice at 35 days post-immunization was significantly upregulated (P < 0.05). The protective efficacy of the vaccine was assessed by challenging with an intraperitoneal injection of 10 LD50 doses of D. nodosus, and the OMVs provided 100 % protection. Histopathological examination and tissue bacterial load detection revealed that the OMVs significantly alleviated tissue damage and bacterial colonization (P < 0.001). These findings provide a valuable reference and new strategies for the development of vaccines against D. nodosus to prevent infectious foot diseases.