Figure 1: Stages in the intracellular life cycle of L. monocytogenes. The cartoon (a) sketches the different stages of L. monocytogenes infection: (I) cell entry mediated by invasion factors InlA or INLB, (II) escape from phagolysosom by LLO and PlcA, (III) actin recruitment and replication, (IV) intracellular movement due to polarized actin-polymerization mediated by ActA, (V) cell-to-cell spread by formation of listeriapods, and (VI) subsequent lysis of the two-membrane vacuole by LLO and PlcB. Modified from Tilney & Portnoy [12]. The fluorescence image (b) shows the intracellular movement and cell-to-cell spread of L. monocytogenes cells (green) driven by the polarized polymerization of actin tails (red).