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15.1.1.3: Listeria monocytogenes

  • Page ID
    42653
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    listeria monocytogenes

    Transmission electron micrograph of Listeria monocytogens (color enhanced) ("listeria monocytogenes" by pennstatenews is licensed under CC BY-NC-ND 2.0)

    Organism

    • Listeria monocytogenes is a Gram-positive small non-spore forming rod which can be mistaken for cocci in specimens
    • Catalase positive
    • Psychrotolerant, being able to grow at temperatures as low as 4°C (refrigeration)

    Habitat

    • Widely distributed
    • Associated with humans and many other types of animal
    • Carried asymptomatically in intestinal flora of a small percentage of people (doi: 10.1007/s10096-002-0835-9)

    Source

    • Most frequently infection occurs through ingestion of contaminated, uncooked food
    • Common foods linked to Listeria infection (listeriosis) are soft cheeses, dairy products, and uncooked refrigerated food products such as deli meats

    Epidemiology

    • Exact incidence is unknown due to asymptomatic infection
    • Usually sporadic, but major outbreaks associated with specific food products occasionally occur
    • Of most concern for newborns, pregnant women, the elderly and people with weak immune systems

    Clinical Disease (Listeriosis)

    • When symptoms are present, listeriosis usually produces mild flu-like symptoms
    • More severe manifestations of the disease include septicemia (blood infection), meningitis and meningoencephalitis
    • Listeriosis is most concerning for pregnant women.  Listeria monocytogenes can cross the placenta and infect a fetus in utero.  This infection often results in miscarriage, stillbirth, or birth a critically ill infant.
    • In non-pregnant adults with clear symptoms of listeriosis, the mortality rate is approximately 30%

    Primary Virulence Factors

    • L. monocytogenes infects intracellularly and uses the host cell actin to push itself from one cell directly into the neighboring cell (Figure \(\PageIndex{1}\)).  In this way the Listeria can evade the immune system to some extent and cross normally protective structures such as the placenta.
    • The major virulence factors of L. monocytogenes include:
      • Internalin which induces phagocytosis and allows the bacterium to enter the mammalian cell
      • listeriolysin O which allows Listeria to escape the phagolysosome and enter the cell cytoplasm
      • ActA which polymerizes the mammalian cell’s actin to form an actin tail which propels the Listeria into the neighboring cell

    clipboard_e17e343f649cbc0f1f784404e1a50f1e8.png

    Figure \(\PageIndex{1}\): Infection of human cells by Listeria monocytogenes. 1) L. monocytogenes induces the cell to engulf it through phagocytosis.  For this step, L. monocytogenes requires internalin (InlA and InlB).  Next, listeriolysin O (LLO) allows the Listeria to escape the phagolysosome into the cell cytoplasm.  ActA then 3) polymerizes the host cell's actin and forms an actin tail which 4) pushes the Listeria into the neighboring cell where the process repeats.  (modified from "File:Infecció de Listeria monocytogenes en cèl·lules no fagocítiques.png" by ÁngelaMM12 is licensed under CC BY-SA 4.0)

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    15.1.1.3: Listeria monocytogenes is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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