The intracellular life cycle of L. monocytogenes has been described in detail [1] . L. monocytogenes can enter either phagocytic or nonphagocytic cells, where it is initially contained in a membranebound vacuole that matures through the endocytic pathway. Following acidification, the bacterium escapes from a vacuole into the host cell cytosol by secreting a cholesterol-dependent poreforming cytolysin, listeriolysin O (LLO) [6] [7] [8] . The precise mechanism by which LLO induces vacuolar destruction and bacterial escape into the cytosol is not completely understood.