Characteristics of invasion-reduced hilA gene mutant of Salmonella Enteritidis in vitro and in vivo.

Salmonella enterica serovar Enteritidis (Salmonella Enteritidis) is a facultative intracellular pathogen that causes huge losses in poultry industry and also food poisoning in humans due to its being a food-borne pathogen. Functions of Invasion-related genes need to be explored, as invasion is a key step for Salmonella infection. In this study, a transposon mutant library of Salmonella Enteritidis isolate SM6 was constructed and screened for the invasion-related genes via incubation with Caco-2 cells. Three stably attenuated mutants were identified for significantly reduced invasion with insertions all in hilA (hyperinvasive locus A) gene. We constructed and evaluated the hilA deletion mutant in vivo and in vitro. SM6△hilA showed significantly reduced ability to invade Caco-2 cells and decreased pathogenicity in chicks. However, the bacterial load and pathological damage in the cecum were significantly higher than those in the SM6 in vivo. Present results provide new evidences for pathogenicity research on Salmonella Enteritidis.