Salmonella enterica serovar Gallinarum (S. 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 S. Gallinarum-induced systemic
infection in chickens. In this study, we deleted the S. Gallinarum UDP-N-acetylglucosamine-1-phosphate
transferase gene, which contributes to the biosynthesis of
enterobacterial common antigen (ECA), and studied the pathogenicity of this wecB::Cm strain in a chicken model of systemic
infection. The wecB::Cm mutant strain showed comparable growth but lower resistance to
bile acid and
nalidixic acid than the wild-type strain in vitro. In the oral
infection model of chickens, the virulence of the wecB::Cm strain was significantly attenuated in vivo. 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 wecB::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 wecB::Cm-infected chickens was significantly lower than that of the chickens infected with the wild-type strain. Furthermore, the attenuated wecB::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 wecB gene is an important
virulence factor of S. Gallinarum in the chicken model of systemic
infection, and the avirulent wecB::Cm mutant could possibly be used as a live-
attenuated vaccine strain for controlling fowl
typhoid.