Abstract: Among the known Listeria strains, only Listeria monocytogenes (Lm) can cause human disease. The expression of most virulence genes is regulated fully or partially by positive regulatory factor A (PrfA) protein encoded by prfA gene. In this study, we adopted homologous recombination method to knock out the prfA gene of the wild strain EGDe, and investigated the biological characteristics of EGDe-ΔprfA by testing growth state, virulence gene expression and Caco-2 cell invasion. There was no difference in the growth status of EGDe-ΔprfA and EGDe as demonstrated by the growth curves. Real time quantitative PCR results showed that the expression levels of plcA and plcB genes increased by 2.5 times and twice, respectively, while the expression levels of inlA, inlB, inlC, actA and vip declined. The expression level of prfA gene was nearly zero. The invasion of Caco-2 cells by EGDe-ΔprfA was one fifth as high as that by the wild strain. The gene-deleted strain can provide an important tool for studying the pathogenic mechanism of the foodborne pathogen Listeria monocytogenes.

Key words: Listeria monocytogenes, prf A, gene knock-out, biological characteristics