Polymyxin B-treated outer membrane vesicles of Campylobacter jejuni as prospective mucosal vaccine candidates in chickens.

Abstract

Campylobacter jejuni (C. jejuni) is the leading cause of bacterial gastroenteritis in humans. Primarily, contaminated poultry meat and meat products account for nearly 80% of human infections. Reducing C. jejuni colonization of the chicken gastrointestinal tract is a key strategy to limit the risk of foodborne transmission to humans. To this end, outer membrane vesicles (OMVs) derived from C. jejuni were shown to have strong immunogenic potential in both avian and mammalian models. However, a major limitation of OMV-based vaccines against C. jejuni is the presence of lipooligosaccharide (LOS) in the outer leaflet of OMVs, which often confers endotoxicity. Additionally, some strains of C. jejuni also express outer-core structures of LOS that mimic human gangliosides, potentially inducing cross-reactive antibody responses. Although avians are less sensitive to endotoxin exposure, a high number of C. jejuni infections in chickens may cause anorexia and impaired nutrient absorption, leading to reduced feed intake and suppressed growth performance in broilers. Here, we explored a simple approach to address the risk of LOS-mediated endotoxic effects of OMVs using a non-ganglioside-mimicking C. jejuni strain (TGH 9011; Penner serotype O: 3). For this, C. jejuni OMVs were treated with an optimal amount of polymyxin B (PMB), a polycationic peptide known to neutralize LOS activity. We confirmed that PMB treatment of C. jejuni LOS substantially reduces the expression of TNFα and IL-1β genes, hallmarks of LOS-driven endotoxic activity. Furthermore, oral administration of chitosan-coated PMB-treated OMVs (CS-PMB-OMVs) retained their ability to induce functional intestinal secretory IgA (sIgA) while eliciting modest cellular immune responses in immunized chickens. Similar to natural OMVs, CS-PMB-OMVs immunized birds exhibited a marked reduction in cecal C. jejuni colonization following C. jejuni infection compared with unvaccinated controls. These findings demonstrate that PMB treatment does not compromise the inherent immunogenicity of natural OMVs, while effectively mitigating the risk of LOS-mediated endotoxicity.