Salmonella Pullorum spiC mutant is a desirable LASV candidate with proper virulence, high immune protection and easy-to-use oral administration

Abstract

Live attenuated Salmonellavaccine (LASV) is considered to be an effective contributory measure during the control of Salmonella infection. A Salmonella Pullorum spiC mutant was evaluated comprehensively as a LASV candidate (LASV-p) for broilers in terms of safety and immunogenicity. LASV-p was adminstered to 3-day broilers by intramuscular injection. The LD₅₀ increased 126 fold, and no tissue lesions were observed in the liver, spleen and cecum, in comparison with the control group inoculated with PBS and a passive group by wild-type Salmonella. Growth rates of all broilers were normal and not affected. LASV-p persisted in vivo until 21 days in liver, 28 days in spleen and 35 days in feces, and induced high levels of humoral IgG and mucosal IgA. Cellular immunity was also stimulated in the form of antigen-specific lymphocyte proliferation and higher counts of CD3⁺CD8⁺ T cells and increased expression of mRNA of Th1 cytokines, IFN-γ and IL-2, in the early stage, and Th2 cytokines, IL-4 and IL-10, in the later stages. LASV-p provided at least 90% immuneprotection against a wild-type Salmonella Pullorum and cross-protection in different degree against other Salmonella searovars. Oral vaccine could also offer high immune protection of 87.5%. These results indicated that LASV-p vaccine candidate had a high level of safety and immune protection and it might be developed as a novel easy-to-use oral vaccine to improve poultry health in the future.

Keywords: Cellular immunity; Immune protection; LASV-p; Live attenuated Salmonella vaccine; Safety; Salmonella Pullorum.