Interactions of Listeria monocytogenes with the autophagy system of host cells.

Macrophages are immune cells that participate in the host defense against bacterial pathogens. These cells mediate bacterial clearance by internalizing bacteria into a phagosome, which ultimately fuses with lysosomes to kill bacteria. One bacterial strategy to evade killing in the phagosome is to escape from this compartment prior to lysosomal fusion. Listeria monocytogenes is a classic example of a "cytosol-adapted pathogen" in that it can rapidly escape from the phagosome in macrophages (and other cell types) and replicate rapidly in the cytosol. Phagosome escape also enables cell-to-cell spread by the bacteria through a bacterial driven actin-based motility mechanism. How the bacteria escape the phagosome and evade host cellular defenses, including autophagy, will be discussed in this review. We also discuss an underappreciated population of L. monocytogenes that can replicate in macrophage vacuoles and how these may be important for the establishment of chronic infections.