15.1.1.3: Listeria monocytogenes
- Page ID
- 42653
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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
Additional information: