[Construction and characterization of Listeria monocytogenes deltaprfA mutant strains].

Objective: Listeria monocytogenes (Lm) is an important pathogen that can cause serious listeriosis in humans and animals. The pathogenicity of Lm has a close relationship with the PrfA protein regulating the expression of virulence genes. Therefore, we studied the regulation functions of PrfA and its role on Lm's virulence.

Methods: The prfA genes of LM4, serotype 1/2a, and F4636, serotype 4b, were deleted by homologous recombination technology, and the biological characteristics of the mutants were further studied.

Results: The prfA gene deleted strains LM4deltaprfA and F4636deltaprfA and their back mutation strains were successfully constructed. The results show that the hemolysis activity was lost in prfA deleted strains and was recovered in the reverse mutant strains. The prfA deleted strains lost phospholipase activity; their adhesion and invasion ability significantly decreased. Furthermore, their 50% lethal doses (LD50) were 5 logs higher comparing with wild type strains.

Conclusion: PrfA regulates hly, plcB and inl gene family and affects significantly Lm's virulence.