Listeria bacteria are attacked by the immune system before they are able to cause infection. Those that escape the immune system's initial response, however, spread through intracellular mechanisms, which protects them from circulating immune factors (AMI). To invade, Listeria induces macrophage phagocytic uptake by displaying D-galactose in their teichoic acids that are then bound by the macrophage's polysaccharides. Other important adhesins are the internalins. Listeria uses internalin A and B to bind to cellular receptors. Internalin A binds to E-cadherin, while internalin B binds to the cell's Met receptors. If both of these receptors have a high enough affinity to Listerias internalin A and B, then it will be able to invade the cell via an indirect zipper mechanism. Once phagocytosed, the bacterium is encapsulated by the host cell's acidic phagolysosome organelle. Listeria, however, escapes the phagolysosome by lysing the vacuole's entire membrane with secreted hemolysin, now characterized as the exotoxin listeriolysin O. The bacteria then replicate inside the host cell's cytoplasm. Listeria must then navigate to the cell's periphery to spread the infection to other cells. Outside the body, Listeria has flagellar-driven motility, sometimes described as a "tumbling motility". However, at 37 °C, flagella cease to develop and the bacterium instead usurps the host cell's cytoskeleton to move. Listeria, inventively, polymerizes an actin tail or "comet", from actin monomers in the host's cytoplasm with the promotion of virulence factor ActA. The comet forms in a polar manner and aids the bacterial migration to the host cell's outer membrane. Gelsolin, an actin filament severing protein, localizes at the tail of Listeria and accelerates the bacterium's motility. Once at the cell surface, the actin-propelled Listeria pushes against the cell's membrane to form protrusions called filopods or "rockets". The protrusions are guided by the cell's leading edge to contact adjacent cells, which then engulf the Listeria rocket and the process is repeated, perpetuating the infection. Once phagocytosed, the bacterium is never again extracellular: it is an intracellular parasite like S. flexneri, Rickettsia spp., and C. trachomatis. Epidemiology The Center for Science in the Public Interest has published a list of foods that have sometimes caused outbreaks of Listeria: hot dogs, deli meats, milk (even if pasteurized), cheeses (particularly soft-ripened cheeses such as feta, Brie, Camembert, blue-veined, or Mexican-style queso blanco), raw and cooked poultry, raw meats, ice cream, raw fruit, vegetables, and smoked fish. Cold-cut meats were implicated in an outbreak in