A novel approach for the generation of Salmonella Gallinarum ghosts and evaluation of their vaccine potential using a prime-booster immunization strategy

A novel, regulatory E-lysis cassette was used in this study to avoid the untimely expression of lysis gene E and to achieve stable and improved production of Salmonella Gallinarum (SG) ghosts. A prime-booster immunization strategy using these ghosts was subsequently utilized with the aim of inducing a robust immune response for the prevention of acute fowl typhoid infection. In the first animal experiment, a total of 54 chickens were equally divided into three groups (n = 18): group A (non-immunized control), group B (prime-boost immunized), and group C (singly immunized). Chickens from both immunized groups demonstrated significant increases in plasma IgG, intestinal secretory IgA, and antigen-specific lymphocyte proliferative responses. After virulent SG challenge, group B chickens immunized with the prime-boost regimen showed optimized protection. In the second animal experiment, total 20 chickens were equally divided into two groups (n = 10): group A (non-immunized control), group B (prime-boost immunized) and the immunogenicity of the ghosts was further evaluated after a booster dose of the immunization. In the second animal experiment, the population of CD3+CD4+ positive T cells in the immunized chickens was significantly higher after booster immunization. In addition, increased gene expression levels of Th1 cytokines, IFN-γ, and IL-2 were observed in SG-specific antigen stimulated peripheral blood mononuclear cells of prime-boost immunized chickens compared to non-immunized chickens. In summary, the current study describes a novel approach for stable production of a safety-enhanced SG ghost preparation, and demonstrates that utilization of a prime-boost immunization strategy has an advantage over single immunization because it induces a robust immune response for optimum protection against fowl typhoid.