catarrhalis

Moraxella catarrhalis, formerly Branhamella catarrhalis, is a Gram-negative, oxidase-positive diplococcus in the family Moraxellaceae. It is a human commensal of the upper respiratory tract and a frequent cause of mucosal infections, particularly in children.

Biology and microbiology: M. catarrhalis is an aerobic, nonmotile bacterium that commonly colonizes the nasopharynx. It grows well on routine culture media and forms smooth, opaque colonies. Many strains produce beta-lactamase, contributing to penicillin resistance and influencing antibiotic choice.

Clinical role: While often a harmless colonizer, M. catarrhalis is a well-recognized pathogen in acute otitis media and sinusitis in children, and in bronchitis or pneumonia in adults, especially those with chronic lung disease. It can also cause conjunctivitis and, less commonly, invasive infections in immunocompromised individuals.

Diagnosis: Diagnosis is typically made from specimens obtained from the site of infection (for example, ear effusion, sinus drainage, or respiratory secretions) using culture and identification by standard biochemical tests, oxidase positivity, and, when available, molecular methods or MALDI-TOF mass spectrometry. The detection of beta-lactamase can guide antibiotic therapy.

Treatment and prevention: Because many strains produce beta-lactamase, penicillin monotherapy is often ineffective. Effective options include amoxicillin-clavulanate and certain cephalosporins, with macrolides as alternatives in some cases. Treatment should be guided by local resistance patterns. There is no widely used vaccine for M. catarrhalis, and prevention focuses on general measures to reduce respiratory infection transmission and appropriate management of infections.