Immunogenic potential and protective efficacy of a sptP deletion mutant of Salmonella Enteritidis as a live vaccine for chickens against a lethal challenge

Salmonella Enteritidis (SE) is a highly adapted pathogen causing severe economic losses in the poultry industry worldwide. Chickens infected by SE are a major source of human food poisoning. Vaccination is an effective approach to control SE infections. This study evaluated the immunogenicity and protective efficacy of a SE sptP deletion mutant (C50336 Delta sptP) as a live attenuated vaccine (LAV) candidate in chickens. 14 day-old specific pathogen-free (SPF) chickens were intramuscularly immunized with various doses of C50336 Delta sptP. Several groups of chickens were challenged with the virulent wild-type SE strain Z-11 via the same route at 14 days post vaccination. Compared to the control group, the groups vaccinated with 1 x 10(6), 1 x 10(7) and 1 x 10(8) colony-forming units (CFU) of C50336 Delta sptP exhibited no clinical symptoms after immunization. Only slight pathological changes occurred in the organs of the 1 x 10(9) CFU vaccinated group. C50336 Delta sptP bacteria were cleared from the organs of immunized chickens within 14 days after vaccination. Lymphocyte proliferation and serum cytokine analyses indicated that significant cellular immune responses were induced after the vaccination of C50336 Delta sptP. Compared to the control group, specific IgG antibody levels increased significantly in vaccinated chickens, and the levels increased markedly after the challenge. The 1 x 10(7), 1 x 10(8), and 1 x 10(9) CFU vaccinated chickens groups showed no clinical symptoms or pathological changes, and no death after the lethal challenge. Whereas severe clinical signs of disease and pathological changes were observed in the control group chickens after the challenge. These results suggest that a single dose of C50336 Delta sptP could be an effective LAV candidate to against SE infection in chickens.