Evaluation of immunogenicity and protective efficacy of Salmonella Gallinarum knockout purB mutant strain in chicken.

A novel SG ΔpurB mutant of Salmonella Gallinarum, showed a strong safety profile as fowl typhoid vaccine candidate. In this study, the immunogenicity and protective efficacy of SG ΔpurB were evaluated following administration via intramuscular (Group A) and oral (Group B) at a dose range of 2 × 108 to 2 × 1010 CFU/200 µL. SG ΔpurB induced robust early humoral and cellular immune responses, with orally vaccinated subgroups B1, B2 and B3 eliciting markedly higher CD4 + T cell response, 45.5%, 46.9% and 36.4% respectively, than intramuscularly immunized birds A1, A2 and A3: 20.9%, 22.5% and 32.2% respectively. CD8 + T cell responses showed a similar trend B1, B2 and B3: 46.3%, 47.2% and 26.5%; A1, A2 and A3: 17.8%, 24.3% and 26.8% respectively. A comparable pattern was also observed for IFN-γ production and humoral IgG titre. Despite the strong initial responses, a gradual decline in immune responses was detected by 3 WPV, CD4 + and CD8 + T cell responses declined across all subgroups, with subgroups receiving higher doses (A2 and B3) retaining relatively elevated responses, underscoring the dose dependent nature of SG ΔpurB immunogenicity. These findings showed that SG ΔpurB is a safe and immunogenic strain, inducing a strong early immune response; however, further optimization, such as adding adjuvants or additional gene deletions, is needed for sustained and effective protection against fowl typhoid.