Expression of listeriolysin and phosphatidylinositol-specific phospholipase C is repressed by the plant-derived molecule cellobiose in Listeria monocytogenes.

The primary habitat of the intracellular pathogen Listeria monocytogenes is considered to be soil and decaying vegetation. As an opportunistic pathogen it must be able to recognize its entry into host tissue and, in response, co-ordinately induce the expression of virulence factors. No signature molecule, which facilitates this regulation, has been identified for any human pathogen. Our studies have demonstrated for the first time that the expression of major virulence determinants in L. monocytogenes can be repressed by an environmentally ubiquitous molecule. Transcriptional hlyA and plcA fusions to luxAB were used to monitor virulent gene expression in the presence of various disaccharides. These studies revealed that the expression of listeriolysin O and phosphatidylinositol-specific phospholipase C is repressed specifically by the plant-derived disaccharide, cellobiose.