Immunogenicity in chickens with orally administered recombinant chicken-borne Lactobacillus saerimneri expressing FimA and OmpC antigen of O78 avian pathogenic Escherichia coli

Purpose. Avian colibacillosis is responsible for economic losses to poultry producers worldwide. To combat this, we aimed to develop an effective oral vaccine for chicken against O78 avian pathogenic Escherichia coli (APEC) infection through a Lactobacillus delivery system. Methodology. Eight Lactobacillus strains isolated from the intestines of broiler chickens were evaluated based on their in vitro adherence ability to assess their potential as a delivery vector. Fimbrial subunit A (FimA) and outer-membrane protein C (OmpC) of APEC with and without fusion to dendritic cell-targeting peptide (DCpep) and microfold cell-targeting peptide (Co1) were displayed on the surface of Lactobacillus saerimneri M-11 and yielded vaccine groups (pPG-ompC-fimA/M-11 and pPG-ompC-fimA-Co1-DCpep/M-11, respectively). The colonization of the recombinant strains in vivo was assessed and the immunogenicity and protective efficacy of orally administered recombinant strains in chickens were evaluated. Results. The colonization of the recombinant strains in vivo revealed no significant differences between the recombinant and wild-type strains. Chickens orally administered with vaccine groups showed significantly higher levels of OmpC/FimA-specific IgG in serum and mucosal IgA in cecum lavage, nasal lavage and stool compared to the pPG/M-11 group. After challenge with APEC CVCC1553, better protective efficacy was observed in chickens orally immunized with pPG-ompC-fimA/M-11 and pPG-ompC-fimA-Co1-DCpep/M-11, but no significant differences were observed between the two groups. Conclusions. Recombinant chicken-borne L. saerimneri M-11 showed good immunogenicity in chickens, suggesting that it may be a promising vaccine candidate against APEC infections. However, the activity of mammalian DCpep and Co1 was not significant in chickens.