wecB Gene of Salmonella Gallinarum Plays a Critical Role in Systemic Infection of Fowl Typhoid

serovar Gallinarum ( . Gallinarum) is a host-specific pathogen causing fowl typhoid, a severe systemic infection in poultry, which leads to substantial economic losses due to high morbidity and mortality in many developing countries. However, less is known about the pathogenic characteristics and mechanism of . Gallinarum-induced systemic infection in chickens. In this study, we deleted the . Gallinarum UDP- -acetylglucosamine-1-phosphate transferase gene, which contributes to the biosynthesis of enterobacterial common antigen (ECA), and studied the pathogenicity of this ::Cm strain in a chicken model of systemic infection. The ::Cm mutant strain showed comparable growth but lower resistance to bile acid and nalidixic acid than the wild-type strain . In the oral infection model of chickens, the virulence of the ::Cm strain was significantly attenuated . Chickens infected with wild-type strain showed typical clinical signs and pathological changes of fowl typhoid and died between 6 and 9 days post-infection, and the bacteria rapidly disseminated to systemic organs and increased in the livers and spleens. In contrast, the ::Cm mutant strain did not cause chicken death, there were no significant clinical changes, and the bacterial numbers in the liver and spleen of the chickens were significantly lower than those of the chickens infected with the wild-type strain. In addition, the expression of interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and CXCLi1 in the livers of ::Cm-infected chickens was significantly lower than that of the chickens infected with the wild-type strain. Furthermore, the attenuated ::Cm strain could persistently colonize the liver and spleen at low levels for up to 25 days post-infection and could induce a protective immune response in the chickens. These results indicate that the gene is an important virulence factor of . Gallinarum in the chicken model of systemic infection, and the avirulent ::Cm mutant could possibly be used as a live-attenuated vaccine strain for controlling fowl typhoid.