1 College of Animal Science and Technology, Yangzhou University, Yangzhou 225009, China; 2 Jiangsu Key Laboratory of Zoonosis, Yangzhou University, Yangzhou 225009, China
Abstract：Salmonella enteritidis (SE) always colonized in the intestinal and reproductive tracts of the poultry, causing direct contamination and vertical transmission of eggs that were difficult to eradicate and prevent. It not only affected the egg production, but also caused egg pollution as well as environmental pollution and imperiled human health. The effect proteins of the type secretion system (T3SS) played a critical role when SE attached to the host cell. In order to study the role of the T3SS1 major effect protein SipC during SE infection, the sipC deletion mutant strain of SE MY1 were constructed by using λRed homologous recombination system, and a complementary strain MY1ΔsipC/psipC was constructed by transformation of the a plasmid pBR322 carrying the sipC gene cloned from MY1. The growth curve, the ability of adhesion and invasive to human (Homo sapiens) colorectaladeno carcinoma cell line (Caco-2) and duck (Anas platyrhynchos) granulosa cell (dGC) of the wild-type strain MY1, mutants MY1ΔsipC and MY1ΔsipC/psipC in vitro were measured. And the strains were orally inoculated to 7-day-old shaoxing ducklings separately to study the pathogenicity of sipC in vivo. The results showed that the mutants MY1ΔsipC and MY1ΔsipC/psipC were successfully constructed and SE MY1 contained a sipC gene with 100% identity to the S. typhimurium. No significant difference was observed between the parental strain MY1 and sipC mutant strains in growth curve. However, after 2 h of infection, the ability of SE MY1ΔsipC adhering to Caco-2 and dGCs were decreased about 44.9% and 34.5%, respectively, as compared with the wild-type adherence, and the invasive ability of SE MY1ΔsipC to Caco-2 and dGCs were also reduced 37.9% and 30.4%, respectively. The virulence of the sipC mutant was significantly reduced in a 7-day-old duckling model of SE disease (P<0.05), as determined by quantifying the lethal dose 50% of the bacterial strains. Collectively, a novel function of sipC in contributes to SE virulence was covered and experimental reference of the interaction between sipC and host genes were offered for further study.
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