Moraxella species

Valeria Fabre, M.D., Paul G. Auwaerter, M.D.

MICROBIOLOGY

  • Gram-negative diplococcus [Fig], appears identical to N. gonorrhoeae.
    • Previously known as Branhamella.
    • M. catarrhalis is the major human pathogen.
      • Occasional cases of other Moraxella species have been described.
        • M. nonliquefaciens has been seen in highly immunocompromised patients. It may occasionally be misidentified in the lab as N. cinerea, N. flavescens, or as a glucose-negative strain of N. gonorrhoeae.
    • Frequently missed in respiratory cultures because colonies resemble commensal Neisseria, which are normal flora.
  • Grows easily on blood chocolate agar, grows well at 28ºC.
  • Colonizes the upper airways in 5-15% of the population; found only in humans.
    • It is most frequently found as part of normal flora for infants and children (25-75% in healthy children) and decreases in adults.
    • Higher prevalence of pharyngeal colonization during winter.
  • Commonly produces beta-lactamase; 95% of strains are resistant to amoxicillin.

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Last updated: June 12, 2025