M. catarrhalis, formerly known as Neisseria catarrhalis, was transferred to the genus Branhamella in 1974. The species is currently in the family Moraxellaceae, which contains three genera: Moraxella, Acinetobacter, and Psychrobacter.
Isolated only from humans, M. catarrhalis is a commensal of the upper respiratory tract. This organism has become an opportunistic pathogen and has been recognized as a cause of upper respiratory tract infection in otherwise healthy children and the elderly.
It also can cause lower respiratory infections, especially in adults with chronic obstructive pulmonary disease. Predisposing factors in the pathogenesis include advanced age, immunodeficiency, neutropenia, and chronic debilitating diseases. M. catarrhalis has been reported as the third most common cause
of acute otitis media and sinusitis in children (Figure 18-13, A). Severe infections are seen in immunocompromised hosts; hospital outbreaks of M. catarrhalis respiratory infections have occurred. The presence of intracellular, gram-negative diplococci in these specimens may alert the microbiologist to possible
infection with M. catarrhalis. Most isolates produce 13-lactamase, making them resistant to ampicillin and amoxicillin, which are commonly used for otitis media.
Specimen Collection and Identification
Specimen collection for M. catarrh alis should be determined by the laboratory according to the various specimen types. The organism will grow on both SBA and CHOC, producing smooth, opaque, gray to white colonies (Figure 18-13, B). The term hockey puck has been used to describe the colony because it remains
intact when pushed across the plate with a loop. M. catarrhalis is usually inhibited on gonococcal selective
agars by the colistin in the media, but some species resistant to this antimicrobial may grow. Like Neisseria species, M. catarrhalis is oxidase and catalase positive.
The organism is asaccharolytic, and it may be differentiated from Neisseria spp. by positive DNase and butyrate esterase reactions. Tributyrin is used as the substrate to detect butyrate esterase activity .