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Listeria monocytogenes Essay

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Listeria monocytogenes

Introduction
Listeria monocytogenes, a motile, gram-positive rod, is an opportunistic food-borne pathogen capable of causing listeriosis in humans. Listeriosis includes manifestations of septicemia, meningitis, pneumonia, and encephalitis. L. monocytogenes is also implicated in miscarriages, stillbirth, and premature birth for pregnant women. L. monocytogenes is a tough bacterium resistant to freezing, drying, and heat; most strains have been shown to be pathogenic. It is hypothesized that 1-10% of humans are intestinal carriers of L. monocytogenes. Over 37 mammalian species, including wild and domestic animals, are capable of L. monocytogenes infection and transmission. Extensive environmental reservoirs for L.
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Pathogenic L. monocytogenes go through an intracellular life cycle involving early escape from the phagocytic vacuole, rapid intracytoplasmic multiplication, bacterially induced actin-based motility, and direct spread to neighboring cells, in which they reinitiate the cycle. The bacterium is first phagocytosed by these cells and secretes a pore-forming toxin called listeriolysin, which allows the bacterium to escape from the phagosome. All virulent strains of L. monocytogenes synthesize and secrete listeriolysin. Phospholipase A and B are other virulence factors that facilitate escape of L. monocytogenes from the phagosome. Once out of the phagosome L. monocytogenes is capable of rapid division in the cytoplasm, evading the immune response and moving throughout the cytoplasm from cell to cell. L. monocytogenes is well known for its ability to propel itself like a rocket through the cell cytoplasm. This is the result of the bacterium’s ability to polymerize actin filaments at its tail end. Actin is arranged in subunits to form microfilaments that are capable of directing cell movement. L. monocytogenes accomplishes cell motility through a virulence factor called ActA that takes advantage of normal actin polymerization going on in the cell. The ActA protein shares sequence homology with a protein called WASP that is found in virtually all eukaryotic cells. WASP is responsible for recognizing and
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