Listeriosis pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]
Overview
Most human infections follow consumption of contaminated food. Rare cases of nosocomial transmission have been reported.
When Listeria bacteria get into a food processing factory, they can live there for years, sometimes contaminating food products. The bacterium has been found in a variety of raw foods, such as uncooked meats and vegetables, as well as in foods that become contaminated after cooking or processing, such as soft cheeses, processed meats such as hot dogs and deli meat (both products in factory-sealed packages and products sold at deli counters), and smoked seafood. Unpasteurized (raw) milk and cheeses and other foods made from unpasteurized milk are particularly likely to contain the bacterium.
Listeria is killed by pasteurization and cooking; however, in some ready-to-eat foods, such as hot dogs and deli meats, contamination may occur after factory cooking but before packaging. Unlike most bacteria, Listeria can grow and multiply in some foods in the refrigerator.
Pathogenesis
Listeriosis typically manifests as gastroenteritis, meningoencephalitis, and mother-to-fetus infections, which reflect its ability to cross the intestinal barrier, blood-brain barrier, and fetoplacental barrier, respectively.
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 though intracellular mechanisms and are therefore guarded against circulating immune factors (AMI).
To invade, Listeria induces macrophage phagocytic uptake by displaying D-galactose receptors that are then bound by the macrophage's polysaccharide receptors (Notably, in most bacterial infections it is the host cell, not the bacteria, that displays the polysaccharide). Once phagocytosed, the bacteria 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, [1] now characterized as the exotoxin listeriolysin O. The bacteria then replicate inside the host cell's cytoplasm.
Listeria must navigate to the cell's periphery to spread the infection to other cells:
- Outside of the body, Listeria has flagellar-driven motility. However, at 37°C, flagella cease to develop and the bacteria instead usurps the host cell's cytoskeleton to move:
- Listeria polymerizes an actin tail or "comet" , using host-produced actin filaments [2] with the promotion of virulence factor ActA.
- The comet forms in a polar manner [3] and aids the bacteria's migration to the host cell's outer membrane.
- Gelsolin, an actin filament severing protein, located 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 [4]to contact adjacent cells which subsequently engulf the Listeria rocket. The process is repeated, perpetuating the infection.
Once phagocytosed, the Listeria is never again extracellular: it is an intracytoplasmic parasite.
Once the bacterium enters the host's monocytes, macrophages, or polymorphonuclear leukocytes, it becomes blood-borne (septicemic) and can grow. Its presence intracellularly in phagocytic cells also permits access to the brain and probably transplacental migration to the fetus in pregnant women.
The pathogenesis of L. monocytogenes centers on its ability to survive and multiply in phagocytic host cells.
Genetics
Listeria monocytogenes encodes virulence factor genes, which are thermoregulated. The expression of virulence factors 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" this structure and allows translation initiation for the virulent genes.
Associated Conditions
Gross Pathology
Microscopic Pathology
References
- ↑ Tinley, L.G.; et al. (1989). "Actin Filaments and the Growth, Movement, and Spread of the Intracellular Bacterial Parasite, Listeria monocytogenes". The Journal of Cell Biology. 109: 1597–1608. Unknown parameter
|quotes=ignored (help) - ↑ "Listeria". MicrobeWiki.Kenyon.edu. 16 August 2006. doi:. Check
|doi=value (help). Retrieved 2007-03-07. - ↑ Laine, R.O.; et al. (1998). "Gelsolin, a Protein That Caps the Barbed Ends and Severs Actin Filaments, Enhances the Actin-Based Motility of Listeria monocytogenes in Host Cells". Infection and Immunity. 66(8): 3775–3782. Unknown parameter
|quotes=ignored (help) - ↑ Galbraith, C.G.; et al. (2007). "Polymerizing Actin Fibers Position Integrins Primed to Probe for Adhesion Sites". Science. 315: 992–995. Unknown parameter
|quotes=ignored (help)