Development and Evaluation of Novel Vaccination Strategies for Campylobacter Control in Poultry

Chicken is the primary natural host of Campylobacter, the leading bacterial cause of human enteritis in the US and other developed countries. Thus, mitigation of Campylobacter in chicken using innovative approaches, such as vaccination, will have a significant impact on food safety and public health. Our previous studies have demonstrated that the two outer membrane proteins, CmeC (the essential component of the CmeABC multi-drug efflux pump) and CfrA (a ferric enterobactin receptor), are feasible candidates for immune intervention against Campylobacter. DNA vaccine has appeared to offer various advantages for poultry, particularly when combined with in ovo vaccination. Chitosan-encapsulated subunit vaccines have also been demonstrated to induce both systemic and mucosal immune response via intranasal vaccination. To further develop effective vaccines to mitigate Campylobacter in poultry, two vaccination strategies that may have potential for mass vaccination on poultry farms were developed and evaluated in this project. To develop effective DNA vaccines for in ovo vaccination, cmeC or cfrA genes were cloned into eukaryotic expression vector pCAGGS with introduction of Kozak sequence to further enhance the production level of inserted genes in eukaryotic cells. Large quantities of DNA vaccines were prepared and used for two independent in ovo vaccination trials to evaluate the immune response and protective efficacy of the validated DNA vaccines. However, in ovo injection of the DNA vaccines at 18th day of embryonation, regardless using neutral lipid-protected vectors or not, failed to trigger significant immune response in broilers. To develop chitosan encapsulated subunit vaccines for intranasal vaccination, the conditions for preparation of nanoparticles using chitosan were optimized. In addition to the pCAGGS-CmeC and pCAGGS-CfrA DNA vaccines, large quantities of recombinant CmeC and CfrA proteins were purified and used for preparing chitosan encapsulated subunit vaccines. A chicken experiment (6 treatment groups with 20 chickens per group) was performed to evaluate immune response and protective efficacy of intranasal immunization with four chitosan encapsulated subunit vaccines. Nevertheless, the intranasal subunit vaccines failed to induce immune response and protection against Campylobacter in chickens.