Microbiology · 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
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 →
- Acute and chronic sinusitis Acute rhinosinusitis →
- COPD exacerbations and bronchitis in adults with chronic lung disease Chronic obstructive pulmonary disease (COPD) →
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:
Prevention
- Hand and cough hygiene
- No vaccine; pneumococcal and Hib vaccines do not cover 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.
Related
Related conditions
← Back to the group: 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 (MSD Manual Professional Edition, 2024); Otitis Media (Acute) (MSD Manual Professional Edition, 2026).
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Representative model, for educational purposes only.