What is Moraxella catarrhalis?

Moraxella catarrhalis: A Respiratory Pathogen

Moraxella catarrhalis is a gram-negative, oxidase-positive diplococcus that commonly colonizes the human respiratory tract and is a significant bacterial pathogen causing respiratory infections, particularly in children and adults with underlying conditions. 1

Microbiology and Characteristics

• M. catarrhalis consists of aerobic, oxidase-positive, gram-negative diplococci
• Less fastidious growth requirements than pneumococci or Haemophilus species
• Grows on simple media without blood or serum 1
• Primary mechanism of β-lactam resistance is β-lactamase production (over 90% of isolates are β-lactamase producers) 1
• Intrinsically resistant to trimethoprim 1

Epidemiology and Colonization

• Colonizes the nasopharynx in early childhood; 78% of children are colonized by 2 years of age 1
• Children are sequentially colonized with different strains of M. catarrhalis 1
• Otitis-prone children are more frequently colonized than healthy children 1
• Colonization increases during winter and during periods of viral upper respiratory infections 1
• Found almost exclusively within the human respiratory tract 2

Clinical Significance and Associated Infections

M. catarrhalis is associated with:

1. Respiratory tract infections:

   • Acute otitis media in children (15-20% of cases) 1
   • Acute bacterial sinusitis (15-20% of cases) 1
   • Acute exacerbations of chronic bronchitis 1, 3
   • Pneumonia, especially in elderly and those with underlying pulmonary disease 4

2. Less common but serious infections:

   • Bacteremia (rare, primarily in young children with risk factors) 5
   • Endocarditis (very rare, even in immunocompetent patients) 6

Risk Factors for Infection

• Young age (children) 5
• Elderly patients 4
• Cigarette smoking (77% of adult patients with M. catarrhalis pneumonia) 4
• Underlying pulmonary diseases (73% of adult patients) 4
• Immunocompromised status (sickle cell disease, AIDS, leukopenia) 5

Clinical Presentation

• Upper respiratory symptoms and fever are common 5
• In adults with pneumonia: dyspnea and productive cough (87%), fever (60%) 4
• Often presents with concurrent otitis media, sinusitis, or pneumonia 5

Antibiotic Resistance and Treatment

• Over 90% of M. catarrhalis isolates produce β-lactamase 1
• Resistant to penicillin and ampicillin due to β-lactamase production 4
• FDA-approved treatments include:
  • Azithromycin for acute bacterial exacerbations of COPD and acute bacterial sinusitis due to M. catarrhalis 3
  • Amoxicillin-clavulanate is effective against M. catarrhalis due to the β-lactamase inhibitor component 7
  • Clarithromycin has demonstrated antimicrobial activity against M. catarrhalis 8

Emerging Research

Recent research has identified potential novel approaches to managing M. catarrhalis:

• Rothia species from the nasal microbiome may inhibit M. catarrhalis colonization through a secreted peptidoglycan endopeptidase called SagA 2
• This suggests potential for microbiome-based or enzyme-based therapeutic approaches

Clinical Pearls

• M. catarrhalis isolated in sputum cultures from symptomatic adults with underlying respiratory diseases should be treated as a pathogen 4
• Consider M. catarrhalis bacteremia in febrile young children with upper respiratory infections and/or acute otitis media, especially those with underlying immune dysfunction 5
• When treating empirically, consider β-lactamase production in selecting appropriate antibiotics 1