Maillard reaction causes suppression of virulence gene expression in Listeria monocytogenes

Many environmental signals affect the expression of virulence genes of the food borne pathogen Listeria monocytogenes. In addition media composition has been shown to suppress levels of haemolytic activity. Using a Pr(plcA)::luxAB reporter gene fusion it was observed that the heat processing of media also reduces the level of virulence gene expression in L. monocytogenes without affecting its growth. Physicochemical factors that are considered to enhance the Maillard reaction were also found to increase the levels of suppression. The results indicate that heat treatment of a multicomponent matrix gives rise to specific inhibitors of the Listeria virulence gene operon.