From the Research
Yes, Moraxella catarrhalis is considered part of the normal flora of the upper respiratory tract in many healthy individuals. This gram-negative diplococcus colonizes the nasopharynx of approximately 1-5% of adults and up to 66% of children, with higher rates in winter months 1. While M. catarrhalis exists as a commensal organism in many people without causing symptoms, it can become an opportunistic pathogen under certain conditions, particularly in individuals with compromised immune systems, chronic obstructive pulmonary disease (COPD), or young children with immature immune responses. The bacterium can transition from harmless colonizer to pathogen when host defenses are weakened or when it gains access to normally sterile sites.
Key Points
- M. catarrhalis is a common cause of acute otitis media in children, and its frequency of isolation has increased with the introduction of conjugate pneumococcal vaccines 1.
- The bacterium is also associated with acute exacerbations of COPD in adults, and occasionally sinusitis or bronchitis 2.
- The ability of M. catarrhalis to persist as normal flora while maintaining pathogenic potential is related to its various virulence factors, including adhesins that promote mucosal attachment and immune evasion mechanisms.
- The majority of M. catarrhalis strains produce beta-lactamase, making them resistant to beta-lactam antibiotics, but they are often susceptible to other antibiotics such as cefuroxime, ciprofloxacin, and erythromycin 3.
Clinical Implications
- M. catarrhalis should be considered a potential pathogen in individuals with underlying respiratory diseases or compromised immune systems, particularly in the context of upper respiratory tract infections 4.
- Antibiotic treatment should be guided by susceptibility testing, as the bacterium can exhibit resistance to certain antibiotics 3.
- Further research is needed to develop effective vaccines against M. catarrhalis, particularly in light of its increasing importance as a pathogen in the post-pneumococcal vaccine era 1.