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For further information, see CMDT Part 33-14: Infections Caused by Moraxella Catarrhalis

Key Features

  • An infection caused by a gram-negative aerobic coccus, Moraxella catarrhalis, which is morphologically and biochemically similar to Neisseria

Clinical Findings

  • Sinusitis, bronchitis, and pneumonia

  • Bacteremia and meningitis have also been reported in immunocompromised patients


  • Culture

  • The organism frequently colonizes the respiratory tract, and differentiation of colonization from infection can be difficult

  • If M catarrhalis is the predominant isolate, therapy should be directed against it


  • Amoxicillin-clavulanate, ampicillin-sulbactam, trimethoprim-sulfamethoxazole, ciprofloxacin, and second- and third-generation cephalosporins

  • Typically produces β-lactamase and, therefore, is usually resistant to ampicillin and amoxicillin

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