[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Gram-positive rods](https://durgical.com/en/microbiology/groups/gram-positive-rods/) › Listeria monocytogenes

[Microbiology](https://durgical.com/en/microbiology/) · [Gram-positive rods](https://durgical.com/en/microbiology/groups/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

## Key points

- Grows in the fridge; ready-to-eat foods.
- Crosses the placenta: miscarriage, newborn sepsis.
- Tumbling motility; actin rockets.
- Cephalosporin resistant: ampicillin.
- Add ampicillin for meningitis in newborns and older adults.

## 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 →](https://durgical.com/en/conditions/listeriosis/)
- Meningitis in newborns, people over 50 and the immunosuppressed [Bacterial meningitis →](https://durgical.com/en/conditions/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:

- [Ampicillin](https://durgical.com/en/pharmacology/ampicillin/)
- [Gentamicin](https://durgical.com/en/pharmacology/gentamicin/)

## 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

## Memory aid

Listeria is the one that loves the fridge: the cold that stops other bacteria feels like home to it.

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/microbiology/listeria-monocytogenes/)

## Related

- [Streptococcus agalactiae](https://durgical.com/en/microbiology/streptococcus-agalactiae/)
- [Streptococcus pneumoniae](https://durgical.com/en/microbiology/streptococcus-pneumoniae/)

## Related conditions

- [Listeriosis](https://durgical.com/en/conditions/listeriosis/)
- [Bacterial meningitis](https://durgical.com/en/conditions/bacterial-meningitis/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Gram-positive rods](https://durgical.com/en/microbiology/groups/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](https://www.cdc.gov/listeria/about/index.html) (CDC, 2024); [Listeriosis](https://www.who.int/news-room/fact-sheets/detail/listeriosis) (WHO, 2018).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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Source: https://durgical.com/en/microbiology/listeria-monocytogenes/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/listeria-monocytogenes/