Colibacillosis is one of the most common and economically devastating
infectious diseases in poultry production worldwide. Innovative universal
vaccines are urgently needed to protect chickens from the
infections caused by genetically diverse avian pathogenic Escherichia coli (APEC).
Enterobactin (Ent) is a highly conserved
siderophore required for E. coli
iron acquisition and pathogenesis. The Ent-specific
antibodies induced by a novel Ent
conjugate vaccine significantly inhibited the in vitro growth of diverse APEC strains. In this study, White Leghorn chickens were immunized with the Ent
conjugate vaccine using a crossed design with two variables, vaccination (with or without) and APEC challenge (O1, O78, or PBS control), resulting in six study groups (9 to 10 birds/group). The chickens were subcutaneously injected with the
vaccine (100 μg per bird) at 7 days of age, followed by booster immunization at 21 days of age. The chickens were intratracheally challenged with an APEC strain (108 CFU/bird) or PBS at 28 days of age. At 5 days post
infection, all chickens were euthanized to examine lesions and APEC colonization of the major organs. Immunization of chickens with the Ent
vaccine elicited a strong immune response with a 64-fold increase in the level of Ent-specific
IgY in serum. The hypervirulent strain O78 caused extensive lesions in lung, air sac, heart, liver, and spleen with significantly reduced lesion scores observed in the vaccinated chickens. Interestingly, the vaccination did not significantly reduce APEC levels in the examined organs. The APEC O1 with low virulence only caused sporadic lesions in the organs in both vaccination and control groups. The Ent
conjugate vaccine altered the bacterial community of the ileum and cecum. Taken together, the findings from this study showed the Ent
conjugate vaccine could trigger a strong specific immune response and was promising to confer protection against APEC
infection.