The effect of sublethal concentrations of benzalkonium chloride on invasiveness and intracellular proliferation of Listeria monocytogenes

Listeria monocytogenes, which survives improper cleaning and disinfection processes are a major source of recontamination of food products, where they can survive or even multiply until consumption. In this study we investigated the effect of sublethal concentration of benzalkonium chloride (BAC) on the virulence of L. monocytogenes using human intestinal, hepatocytic and macrophage-like cells, three cell types involved in the human infection pathway of L. monocytogenes. Therefore we used four different strains, the type strain EGDe and three isolates from food or food processing environment, which revealed different susceptibility to BAC. Incubation of L. monocytogenes with sublethal concentrations of BAC reduced the invasiveness of all four strains in all three types of cells, respectively. However, a significant decrease could only be observed in the strains more sensitive to BAC. Furthermore sublethal concentration of BAC increased significantly the intracellular proliferation for all four strains in all three different human cell types. Interestingly, this effect of disinfectants on the virulence of L. monocytogenes was maintained even after 24 h incubation in a nutrient-rich broth, which mimics the food matrix. In conclusion we showed that exposure of L. monocytogenes to sublethal concentrations of disinfectants, although reducing invasion, supports the survival and growth of intracellular bacteria. tudy underlines the importance of proper disinfection in food processing environment to limit the number of L. monocytogenes foodborne illnesses.