SiiE Is Secreted by the Salmonella enterica Serovar Typhimurium Pathogenicity Island 4-Encoded Secretion System and Contributes to Intestinal Colonization in Cattle

ABSTRACT Here we report that Salmonella enterica serovar Typhimurium pathogenicity island 4 carries a type I secretion system ( siiCDF ) which secretes an ∼600-kDa protein (encoded by siiE ). SiiE is surface expressed, and its production is regulated by HilA. SiiE and SiiF influence colonization in cattle and the invasion of bovine enterocytes.