From the Guidelines
Moraxella is not typically considered part of the normal human flora, as it is more commonly associated with infections rather than providing beneficial functions as a commensal bacterium. Moraxella species, particularly Moraxella catarrhalis, are gram-negative diplococci that are generally regarded as pathogenic organisms rather than commensal bacteria 1. While they can be found in the upper respiratory tract of some individuals, especially children, without causing symptoms, they are more commonly associated with infections such as otitis media (ear infections), sinusitis, and exacerbations of chronic obstructive pulmonary disease (COPD) 1.
Key Points
- The respiratory tract has its own established normal flora, which typically includes species of Streptococcus, Haemophilus, Corynebacterium, and Neisseria, but Moraxella is generally considered an opportunistic colonizer rather than a standard component of healthy human microbiota.
- Moraxella catarrhalis is often found in the upper respiratory tract of individuals with chronic wet cough and protracted bacterial bronchitis, and is typically treated with antibiotics such as amoxicillin-clavulanate 1.
- The British Thoracic Society guideline for bronchiectasis in adults recommends treating Moraxella catarrhalis infections with amoxicillin-clavulanic acid 625 mg three times a day for 14 days, with alternative treatments including clarithromycin, doxycycline, and ciprofloxacin 1.
Treatment Considerations
- The choice of antibiotic treatment for Moraxella catarrhalis infections should be based on the severity of the infection, the patient's medical history, and the results of antimicrobial susceptibility testing.
- It is essential to note that Moraxella species are opportunistic pathogens that can cause disease when conditions are favorable, and therefore, treatment should be tailored to the individual patient's needs.
From the Research
Moraxella as Normal Flora
- Moraxella catarrhalis is considered to be part of the normal human flora in the upper respiratory tract 2, 3, 4.
- It is a human-restricted commensal of the normal bacterial flora in the upper respiratory tract of children 3.
- The prevalence of colonization of the upper respiratory tract is high in infants and children but decreases substantially in adulthood 4.
Pathogenic Nature of Moraxella
- Moraxella catarrhalis has been recognised as a true human pathogen, causing various upper and lower respiratory tract infections 2, 3, 5, 4.
- It is the third most common pathogen causing acute otitis media in children 3.
- M. catarrhalis causes an estimated 2-4 million exacerbations of chronic obstructive pulmonary disease in adults annually in the United States 4.
Antibiotic Susceptibility
- Most strains of Moraxella catarrhalis produce beta-lactamase and are thus resistant to ampicillin but susceptible to several classes of oral antimicrobial agents 5, 4.
- Antibiotic susceptibility testing has shown that M. catarrhalis isolates are sensitive to amoxicillin-clavulanate, doxycycline, clarithromycin, levofloxacin, and trimethoprimsulfamethoxazole 5.