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Moraxella catarrhalis
Scientific classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Gammaproteobacteria
Order: Pseudomonadales
Family: Moraxellaceae
Genus: Moraxella
Species: M. catarrhalis
Binomial name
Moraxella catarrhalis

Moraxella catarrhalis is a Gram-negative, aerobic, oxidase-positive diplococcus that may both colonize and cause respiratory tract-associated infection in humans.



M. catarrhalis was previously placed in a separate genus named Branhamella. The rationale for this was that other members of the genus Moraxella are rod-shaped and rarely caused infections in humans. However results from DNA hybridization studies and 16S rRNA sequence comparisons were used to justify inclusion of the species catarrhalis in the genus Moraxella. Consequently, the name Moraxella catarrhalis is currently preferred for these bacteria. Nevertheless, some in the medical field continue to call these bacteria Branhamella catarrhalis.

Moraxella is named after Victor Morax, a Swiss ophthalmologist who first described this genus of bacteria. Catarrhalis is derived from catarrh, originally a Greek word meaning 'to flow down', describing the profuse discharge from eyes and nose typically associated with severe inflammation in colds.

Clinical significance

Clinically, these bacteria are known to cause otitis media,[1][2] bronchitis, sinusitis, and laryngitis. Elderly patients and long-term heavy smokers with chronic pulmonary disease should be aware that M. catarrhalis is associated with bronchopneumonia, as well as exacerbations of existing chronic obstructive pulmonary disease (COPD).

The peak rate of colonisation by M. catarrhalis appears to occur at approximately 2 years of age, with a striking difference in colonisation rates between children and adults (very high to very low).

Current research priorities involve trying to find a suitable vaccine[3] for this genotypically diverse organism, as well as determining factors involved with virulence e.g. complement resistance. Lipooligosaccharide is considered one possible virulence factor.[3]



Treatment options include antibiotic therapy or a so-called "watchful waiting" approach. The great majority of clinical isolates of this organism produce beta-lactamases and are resistant to penicillin. Resistance to trimethoprim, trimethoprim-sulfamethoxazole (TMP-SMZ) and tetracycline have been reported. It is susceptible to fluoroquinolones, most second and third generation cephalosporins, erythromycin and amoxicillin-clavulanate.



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