Microbiology · Gram-positive rods
Listeria monocytogenes !
- Bacterium
- Gram-positive
- Exam priority: medium
A bacterium of chilled foods that can cause miscarriage, newborn sepsis and meningitis in pregnant women, newborns, older and immunosuppressed people.
Updated 2026-11-01
Also called: listeria
At a glance
- Gram
- Gram-positive
- Shape
- Short rod, sometimes coccobacillary
- Oxygen
- Facultative anaerobe
- Family
- Listeriaceae
- Stain
- Gram positive; no spores
Morphology
- Short Gram-positive rod
- Tumbling motility at room temperature
- Narrow beta-haemolysis
Transmission
- Ready-to-eat foods: deli meats, soft cheeses, unpasteurised dairy, cold-smoked fish
- From mother to fetus across the placenta or during birth
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Grows at fridge temperature
- Listeriolysin O: lets it escape the phagosome
- Uses host actin («actin rockets») to move from cell to cell
- Intracellular pathogen: cell-mediated immunity is the key defence
Diseases it causes
- Invasive listeriosis (bacteraemia, infection in pregnancy) Listeriosis →
- Meningitis in newborns, people over 50 and the immunosuppressed Bacterial meningitis →
Clinical picture
- Pregnant woman with fever and mild flu-like illness; risk of miscarriage or stillbirth
- Newborn sepsis or meningitis
- Febrile gastroenteritis in healthy people
Diagnosis
- Blood and cerebrospinal fluid cultures
- Gram-positive rods in the cerebrospinal fluid
- Tumbling motility; CAMP positive
Treatment
Ampicillin, often with gentamicin in invasive disease; trimethoprim-sulfamethoxazole is an alternative in allergy. Cephalosporins are inactive, which is why ampicillin is added to empirical meningitis treatment in newborns and older adults.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- In pregnancy, avoiding unpasteurised soft cheeses, deli meats and cold cuts that are not reheated
- Separating raw and cooked foods; cleaning the fridge
- Food safety teaching for pregnant and immunosuppressed people
Test yourself
Think of the answer, then tap the question to see it.
Which feature of Listeria explains outbreaks from chilled foods?
It survives and multiplies at fridge temperature.
Why is ampicillin added to empirical meningitis treatment in people over 50?
To cover Listeria monocytogenes, which is resistant to cephalosporins.
How does Listeria move from one cell to the next?
It polymerises host actin («actin rockets») and pushes into the neighbouring cell without leaving into the extracellular space.
Related
Related conditions
← Back to the group: Gram-positive rods
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: About Listeria Infection (CDC, 2024); Listeriosis (WHO, 2018).
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Representative model, for educational purposes only.