Moraxella

Moraxella is a genus of Gram-negative, aerobic, nonmotile coccobacilli in the family Moraxellaceae. Members are oxidase-positive and typically occur as diplococci or short rods. They colonize human and animal mucous membranes, especially the upper respiratory tract, and are found in the environment. The genus includes several clinically relevant species such as Moraxella catarrhalis, Moraxella lacunata, Moraxella osloensis, and Moraxella nonliquefaciens. The name honors Victor Morax, who described related organisms.

Moraxella catarrhalis is the best-known pathogen in the genus. It is a common cause of acute otitis media, sinusitis, bronchitis and community-acquired pneumonia, and can also cause conjunctivitis. Many strains produce beta-lactamase, reducing susceptibility to penicillin and ampicillin; effective therapy includes amoxicillin-clavulanate or beta-lactamase–stable cephalosporins. Moraxella lacunata is classically associated with angular conjunctivitis. M. osloensis and M. nonliquefaciens are part of normal flora but may cause opportunistic infections in immunocompromised or hospitalized patients.

Diagnosis rests on Gram staining showing Gram-negative diplococci or coccobacilli, oxidase- and catalase-positive reactions, and culture on standard media (blood or chocolate agar). Identification can be aided by biochemical panels, MALDI-TOF mass spectrometry, or molecular methods.

Epidemiology and clinical note: Moraxella species are common colonizers of the nasopharynx; invasive disease is uncommon but may occur in vulnerable individuals. There is no widely used vaccine against Moraxella catarrhalis.