Immunization of Chickens with the Enterobactin Conjugate Vaccine Reduced Campylobacter jejuni Colonization in the Intestine

Campylobacter jejuni is the leading bacterial cause of human enteritis in developed countries. Chicken is the major animal reservoir of C. jejuni and a powerful infection model for human campylobacteriosis. No commercial vaccine against C. jejuni is available to date. The high affinity iron acquisition mediated through enterobactin (Ent), a small siderophore, plays a critical role in the colonization of C. jejuni in the intestine. Recently, an innovative Ent conjugate vaccine has been demonstrated to induce high-level of Ent-specific antibodies in rabbits; the Ent-specific antibodies displayed potent binding ability to Ent and inhibited Ent-dependent growth of C. jejuni. In this study, using specific-pathogen-free (SPF) chickens, we performed three trials to evaluate the immunogenicity of the Ent conjugate vaccine and its efficacy to control C. jejuni colonization in the intestine. The purified Ent was conjugated to the carrier keyhole limpet hemocyanin (KLH). Intramuscular immunization of chickens with the Ent-KLH conjugate for up to three times did not affect the body weight gain, the development of major immune organs and the gut microbiota. In the first two trials, immunizations of chickens with different regimens (two or three times of vaccination) consistently induced strong Ent-specific immune response when compared to control group. Consistent with the high-level of systemic anti-Ent IgG, C. jejuni colonization was significantly reduced by 3-4 log(10) units in the cecum in two independent vaccination trials. The third trial demonstrated that single Ent-KLH vaccination is sufficient to elicit high level of systemic Ent-specific antibodies, which could persist for up to eight weeks in chickens. Taken together, the Ent-KLH conjugate vaccine could induce high-level of Ent-specific antibodies in chickens and confer host protection against C. jejuni colonization, which provides a novel strategy for Campylobacter control in poultry and humans.