Listeria Pathogenesis
Listeria uses the cellular machinery to move around inside the host cell: It induces directed polymerization of actin by the ActA transmembrane protein, thus pushing the bacterial cell around.
Listeria monocytogenes, for example, encodes virulence genes that are thermoregulated. The expression of virulence factor is optimal at 37 degrees Celsius and is controlled by a transcriptional activator, PrfA, whose expression is thermoregulated by the PrfA thermoregulator UTR element. At low temperatures, the PrfA transcript is not translated due to structural elements near the ribosome binding site. As the bacteria infect the host, the temperature of the host melts the structure and allows translation initiation for the virulent genes.
The majority of Listeria bacteria are targeted 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 and are, therefore, guarded against 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 polysaccharide receptors. Other important adhesins are the internalins.
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 bacteria's 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 listeria is never again extracellular: it is an intracytoplasmic parasite like Shigella flexneri and Rickettsia.
Listeria monocytogenes, for example, encodes virulence genes that are thermoregulated. The expression of virulence factor is optimal at 37 degrees Celsius and is controlled by a transcriptional activator, PrfA, whose expression is thermoregulated by the PrfA thermoregulator UTR element. At low temperatures, the PrfA transcript is not translated due to structural elements near the ribosome binding site. As the bacteria infect the host, the temperature of the host melts the structure and allows translation initiation for the virulent genes.
The majority of Listeria bacteria are targeted 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 and are, therefore, guarded against 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 polysaccharide receptors. Other important adhesins are the internalins.
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 bacteria's 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 listeria is never again extracellular: it is an intracytoplasmic parasite like Shigella flexneri and Rickettsia.
Listeria Pathogenesis
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