Moraxella — a genus of Gram-negative bacteria

Characteristics

Moraxella species are typically short rods or diplococci when viewed under the microscope. They are non-motile, aerobic or facultatively aerobic, and are often oxidase-positive. Many are asaccharolytic or slowly fermentative, meaning they do not rapidly use sugars for energy. Colonies grown on routine media tend to be smooth and opaque. These phenotypic traits help distinguish Moraxella in clinical microbiology laboratories.

Species and clinical importance

Some notable species include:

• Moraxella catarrhalis — a frequent inhabitant of the human respiratory tract and a recognized cause of otitis media, sinusitis, bronchitis and exacerbations of chronic obstructive pulmonary disease (COPD).
• Moraxella lacunata and Moraxella osloensis — associated mainly with ocular infections such as conjunctivitis and occasional systemic infections in susceptible hosts.

Laboratory identification and treatment

Identification relies on culture, microscopy and simple biochemical tests (oxidase reaction, DNAse activity, and other routine assays). An important clinical feature is that many strains of M. catarrhalis produce beta-lactamase enzymes, which can inactivate plain penicillins. This has practical implications for therapy: beta-lactam/beta-lactamase inhibitor combinations and several alternative antibiotic classes are commonly used where treatment is necessary. Clinical decisions should follow local guidelines and susceptibility testing.

History and taxonomy

Organisms now placed in Moraxella were previously described under different names; for example, M. catarrhalis was long known as Branhamella catarrhalis before taxonomic revision. Historical descriptions and some early ophthalmic reports are connected to Victor Morax, the eponymous physician and researcher (ophthalmologist). For further reading and resources see background pages: Gram stain and morphology and general references on microbial pathogens here and here.