[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Gram-negative cocci](https://durgical.com/en/microbiology/groups/gram-negative-cocci/) › Moraxella catarrhalis

[Microbiology](https://durgical.com/en/microbiology/) · [Gram-negative cocci](https://durgical.com/en/microbiology/groups/gram-negative-cocci/)

# Moraxella catarrhalis

- Bacterium
- Gram-negative
- For completeness

A nose and throat bacterium that causes ear infections in children, sinusitis and COPD flares.

Updated 2026-11-01

## Key points

- The three otitis media bacteria: S. pneumoniae, nontypeable H. influenzae and M. catarrhalis.
- Nearly every strain makes beta-lactamase: amoxicillin-clavulanate is used.
- Second bacterial cause of COPD exacerbation, after nontypeable H. influenzae.
- Colonies that glide like a hockey puck on ice.

## At a glance

**Gram**
Gram-negative

**Shape**
Diplococcus

**Oxygen**
Aerobic

**Family**
Moraxellaceae

**Stain**
Gram: red diplococci

## Morphology

- Gram-negative diplococci that look like Neisseria
- Oxidase-positive; does not ferment sugars
- Colonies slide intact across the agar when pushed with a loop ("hockey puck")

## Transmission

- Respiratory droplets and secretions; colonizes the nasopharynx of many children

**Reservoir:** Humans only (respiratory tract)

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Virulence factors

- Beta-lactamase (BRO enzymes) in nearly all strains: destroys amoxicillin and can shield neighboring bacteria
- Adhesins and outer membrane proteins that resist complement
- Lipooligosaccharide (LOS)

## Diseases it causes

- Acute otitis media in children (third most common bacterium) [Acute otitis media →](https://durgical.com/en/conditions/acute-otitis-media/)
- Acute and chronic sinusitis [Acute rhinosinusitis →](https://durgical.com/en/conditions/acute-rhinosinusitis/)
- COPD exacerbations and bronchitis in adults with chronic lung disease [Chronic obstructive pulmonary disease (COPD) →](https://durgical.com/en/conditions/chronic-obstructive-pulmonary-disease/)

## Diagnosis

- Culture of middle ear fluid, sinus aspirate or sputum
- Oxidase-positive Gram-negative diplococci that do not ferment sugars
- Positive beta-lactamase test

## Treatment

Beta-lactamase-stable antibiotics: amoxicillin with clavulanic acid, second- or third-generation cephalosporins, macrolides or trimethoprim-sulfamethoxazole. Amoxicillin alone fails because of the beta-lactamase.

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

In Pharmacology:

- [Amoxicillin](https://durgical.com/en/pharmacology/amoxicillin/)
- [Ceftriaxone](https://durgical.com/en/pharmacology/ceftriaxone/)
- [Azithromycin](https://durgical.com/en/pharmacology/azithromycin/)

## Prevention

- Hand and cough hygiene
- No vaccine; pneumococcal and Hib vaccines do not cover it

## Memory aid

"Moraxella eats the amoxicillin": its beta-lactamase destroys the drug, so clavulanate is added to protect it.

## Test yourself

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

## Which three bacteria cause most bacterial acute otitis media?

Streptococcus pneumoniae, nontypeable Haemophilus influenzae and Moraxella catarrhalis.

## Why does amoxicillin alone often fail against Moraxella?

Nearly all strains make beta-lactamase, so the drug is paired with an inhibitor such as clavulanic acid.

## Which colony behavior is a classic lab clue?

Colonies slide intact across the agar when pushed, like a hockey puck.

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

## Related

- [Haemophilus influenzae](https://durgical.com/en/microbiology/haemophilus-influenzae/)
- [Neisseria meningitidis](https://durgical.com/en/microbiology/neisseria-meningitidis/)

## Related conditions

- [Acute otitis media](https://durgical.com/en/conditions/acute-otitis-media/)
- [Acute rhinosinusitis](https://durgical.com/en/conditions/acute-rhinosinusitis/)
- [Chronic obstructive pulmonary disease (COPD)](https://durgical.com/en/conditions/chronic-obstructive-pulmonary-disease/)

## 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-negative cocci](https://durgical.com/en/microbiology/groups/gram-negative-cocci/)

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

Sources: [Moraxella catarrhalis Infection](https://www.msdmanuals.com/en-au/professional/infectious-diseases/gram-negative-cocci-and-coccobacilli/moraxella-catarrhalis-infection) (MSD Manual Professional Edition, 2024); [Otitis Media (Acute)](https://www.msdmanuals.com/professional/ear-nose-and-throat-disorders/middle-ear-and-tympanic-membrane-disorders/otitis-media-acute) (MSD Manual Professional Edition, 2026).

## **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/moraxella-catarrhalis/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/moraxella-catarrhalis/