Antibacterial effect of E. coli Outer Membrane Vesicles Vaccine-Specific IgY Against Diverse Selection of APEC

Abstract Background : The protective effect of vaccine induced immunoglobulin Y (IgY), specific to outer membrane vesicles (OMVs) from a hyper-vesiculating Escherichia coli mutant was investigated in vitro by using growth inhibition assay and chicken macrophage protection assay. E. coli is a major cause of disease and mortality in the poultry industry. Disease prevention is complicated by antigenically diverse bacterial strains, resulting in limited cross-protection from current vaccines. Here, we tested the antibacterial activity of vaccine- specific IgY (IgY-EVax/02) induced by a novel E. coli vaccine, based on OMVs. A total of 42 Ross 308 broiler breeder hens in lay (23 weeks of age) were immunized via aerosol vaccination, and IgY-EVax/02 antibodies were subsequently extracted from the egg yolks. The antimicrobial effect was assessed by two methods: i) an E. coli growth inhibition assay conducted in a Bioscreen C Analysis with one homologues E. coli ST117 and eight other heterologous strains (ST23, ST69, ST95, ST131, ST23, ST428, and ST6285) commonly associated with disease in poultry. 2) The chicken macrophage protection assay, based on avian macrophage HD11 cells. Result : Bacterial growth was reduced by almost 55% after 15 hours of incubation in the presence of IgY-EVax/02 independent of the E. coli strain tested. In the chicken macrophage protection assay, the effect of bacterial exposure on fully differentiated HD11 cell monolayers was assessed visually and by measuring lactate dehydrogenase (LDH) concentration. Cells treated with IgY-EVax/02 preserved cell integrity and released significantly less LDH upon exposure to the broad panel of E. coli indicating that the IgY inhibited bacterial cell damage. Conclusion : The findings indicate a clear inhibitory effect of IgY-EVax/02 on E. coli growth and host cell-toxicity, suggesting the vaccine potential of disease prevention against a broad variety of avian pathogenic E. coli types.