[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Intracellular and atypical bacteria](https://durgical.com/en/microbiology/groups/intracellular-and-atypical-bacteria/) › Mycoplasma pneumoniae

[Microbiology](https://durgical.com/en/microbiology/) · [Intracellular and atypical bacteria](https://durgical.com/en/microbiology/groups/intracellular-and-atypical-bacteria/)

# Mycoplasma pneumoniae

- Bacterium
- Does not Gram-stain
- Droplet
- Exam priority: medium

A tiny wall-less bacterium that causes «walking pneumonia» in children and young adults; penicillin does not affect it.

Updated 2026-11-01

## Key points

- No wall: not seen on Gram and resistant to beta-lactams
- The only bacterium with cholesterol in its membrane
- Cold agglutinins (IgM): haemolytic anaemia
- Young people in schools or barracks with «walking» pneumonia

## At a glance

**Gram**
Does not Gram-stain

**Shape**
Pleomorphic (no fixed shape); cell with an attachment tip

**Oxygen**
Facultative aerobe

**Family**
Mycoplasmataceae

**Stain**
Does not stain with Gram (no wall)

**Size**
One of the smallest free-living bacteria

## Morphology

- No cell wall; membrane contains sterols (cholesterol)
- Tiny «fried-egg» colonies on special media, after weeks

## Transmission

- Respiratory droplets from coughing or sneezing, with close contact
- Outbreaks in schools, barracks, boarding schools and households

**Reservoir:** Humans only

### Isolation precautions

What the care team adds to standard precautions.

**Droplet**
Surgical mask within about a metre; single room.

## Virulence factors

- P1 adhesin: attaches to ciliated epithelium and paralyses it
- CARDS toxin and hydrogen peroxide damage the respiratory epithelium
- Induces IgM antibodies against red cells (cold agglutinins)

## Diseases it causes

- Atypical («walking») community-acquired pneumonia [Community-acquired pneumonia →](https://durgical.com/en/conditions/community-acquired-pneumonia/)
- Tracheobronchitis, pharyngitis; cold-agglutinin haemolytic anaemia; erythema multiforme

## Clinical picture

- Persistent dry cough, headache and low-grade fever; the patient looks better than expected
- Interstitial infiltrates on X-ray
- Children under five may present with wheezing or diarrhoea

## Diagnosis

- PCR on a respiratory swab: method of choice
- IgM serology; cold agglutinins are a classic but non-specific clue
- Not seen on Gram; culture is slow and rarely used

## Treatment

Macrolides (azithromycin) first; doxycycline or respiratory fluoroquinolones as alternatives. Beta-lactams fail because there is no wall. Macrolide resistance is high in some regions, especially Asia.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Azithromycin](https://durgical.com/en/pharmacology/azithromycin/)
- [Doxycycline](https://durgical.com/en/pharmacology/doxycycline/)

## Prevention

- Hand and cough hygiene
- Droplet precautions in hospital: surgical mask within about a metre

## Memory aid

Mycoplasma «goes out without a coat»: with no wall, Gram has nothing to stain and penicillin nothing to bite; it keeps warm with cholesterol stolen from the host.

## Test yourself

Think of the answer, then tap the question to see it.

## Why is Mycoplasma not seen on Gram stain?

Because it has no peptidoglycan cell wall.

## Which haematological complication is linked to M. pneumoniae?

Cold-agglutinin haemolytic anaemia (IgM antibodies against the I antigen).

## Which isolation precaution does nursing apply for Mycoplasma pneumonia?

Droplet precautions, on top of standard precautions.

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

## Related

- [Mycoplasma genitalium / Ureaplasma](https://durgical.com/en/microbiology/mycoplasma-genitalium-ureaplasma/)
- [Chlamydia pneumoniae / Chlamydia psittaci](https://durgical.com/en/microbiology/chlamydia-pneumoniae-chlamydia-psittaci/)

## Related conditions

- [Community-acquired pneumonia](https://durgical.com/en/conditions/community-acquired-pneumonia/)

## 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.

**Contact**
Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.

**Droplet**
Surgical mask within about a metre; single room.

**Airborne**
N95 respirator and a negative-pressure room.

[← Back to the group: Intracellular and atypical bacteria](https://durgical.com/en/microbiology/groups/intracellular-and-atypical-bacteria/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [About Mycoplasma pneumoniae Infection | M. pneumoniae | CDC](https://www.cdc.gov/mycoplasma/about/index.html) (Centers for Disease Control and Prevention (CDC), 2025).

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Representative model, for educational purposes only.

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