Critical Involvement of the Thioredoxin Reductase Gene () in Gallinarum-Induced Systemic Infection in Chickens.

serovar Gallinarum biovar Gallinarum (SG) causes fowl typhoid, a notifiable infectious disease in poultry. However, the pathogenic mechanism of SG-induced systemic infection in chickens remains unclear. Thioredoxin reductase (TrxB) is a redox protein crucial for regulating various enzyme activities in serovar, but the role in SG-induced chicken systemic infection has yet to be determined. Here, we constructed a mutant SG strain lacking the gene (::Cm) and used chicken embryo inoculation and chicken oral infection to investigate the role of gene in the pathogenicity of SG. Our results showed that ::Cm exhibited no apparent differences in colony morphology and growth conditions but exhibited reduced tolerance to HO and increased resistance to bile acids. In the chicken embryo inoculation model, there was no significant difference in the pathogenicity of ::Cm and wild-type (WT) strains. In the chicken oral infection, the WT-infected group exhibited typical clinical symptoms of fowl typhoid, with complete mortality between days 6 and 9 post infection. In contrast, the ::Cm group showed a 100% survival rate, with no apparent clinical symptoms or pathological changes observed. The viable bacterial counts in the liver and spleen of the ::Cm-infected group were significantly reduced, accompanied by decreased expression of cytokines and chemokines (IL-1β, IL-6, IL-12, CXCLi1, TNF-α, and IFN-γ), which were significantly lower than those in the WT group. These results show that the pathogenicity of the -deficient strain was significantly attenuated, indicating that the gene is a crucial virulence factor in SG-induced systemic infection in chickens, suggesting that may become a potentially effective target for controlling and preventing SG infection in chickens.