Deletion of Nox from Listeria monocytogenes Strain EGDe Enhances Bacterial Virulence and Reduces the Production of Reactive Oxygen Species and Inflammatory Factors In Vivo

The foodborne pathogens have a serious threat to human health, especially Listeria monocytogenes. NADPH oxidase (NOX) is involved in cellular respiration and the production of reactive oxygen species (ROS), acting as messengers to host cells during the infection. However, the role of nox in the process of L. monocytogenes infection is unclear. In this study, we examined the impact of nox in L. monocytogenes by gene deletion. The results of cell experiment showed that knocking out nox from L. monocytogenes strain EGDe resulted in a twofold increase invasion ability to Caco-2 cells compared with that of wild-type strain (WT), but did not affect adhesion ability. Animal infection assays also showed that bacterial loads in the liver and spleen of mice challenged with EGDe-Delta nox were approximately two times higher compared with those challenged with the WT strain. On the one hand, quantitative real-time polymerase chain reaction revealed that deletion of nox leads to upregulation of genes related to the internalization of L. monocytogenes (inlA, inlB, and inlC). More importantly, the expression of listeriolysin-positive regulatory (prfA) gene increased by three times in vivo compared with that of WT. On the other hand, the deletion of nox resulted in a reduction of the upregulation of proinflammatory factors in EGDe-Delta nox compared with the WT and complementary strains. Thus, our study revealed that nox affected the virulence of L. monocytogenes by upregulating the expression of virulence genes and regulating the production of ROS and inflammatory factors in vivo.