Moraxella catarrhalis Infection Workup

Updated: Mar 22, 2021
  • Author: Michael Constantinescu, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Laboratory Studies

A complete blood count (CBC) should be obtained. An increased white blood cell (WBC) count with neutrophilia may be present.

Gram-negative diplococci are found on Gram staining of cultures. Strict adherence to the staining protocol is required. The accuracy of Gram staining for isolation of Neisseria or Moraxella species has been reported to agree perfectly with identification by culture. [19]

Confirmation of the diagnosis of M catarrhalis infection is based on isolation of the organism in culture. Cultures can be taken from middle ear effusion, the nasopharynx, sputum, sinus aspirates, transtracheal or transbronchial aspirates, blood, peritoneal fluid, wounds, or urine. Colonies are approximately 0.2 cm in diameter, opaque, and nonhemolytic after incubation on chocolate or blood agar for 48 hours. Characteristically, colonies can be pushed along the surface of the agar like a hockey puck.

With standard methods of identification, M catarrhalis can be differentiated from Neisseria species by not using sucrose, glucose, maltose, and lactose. Because Neisseria cinerea exhibits the same reaction pattern, the Superoxyl test must be added. For definitive identification, deoxyribonuclease (DNase) and nitrate reduction tests are performed; M catarrhalis produces DNase and reduces nitrate and nitrite levels.

Several rapid confirmatory tests are available to identify M catarrhalis, and they are all based on the ability of M catarrhalis to hydrolyze tributyrin. This provides immediate identification and separation from human Neisseria species, which do not hydrolyze tributyrin.

Serologic tests for infections with M catarrhalis are not widely used; cross-reactivity with Neisseria species in the detection of complement fixation antibodies by immunoelectrophoresis has been demonstrated. Serum antibodies to whole-cell proteins, to lipo-oligosaccharides, and to outer-membrane antigens have proved useful in the diagnosis of M catarrhalis infection. Other laboratory studies may be needed, depending on the site of infection and underlying conditions.


Imaging Studies

Imaging studies (eg, plain radiography or computed tomography [CT]) may be needed, depending on the site of infection.

Paranasal sinus radiography or CT scanning may be helpful. Chest radiography is often performed. If peritonitis is a possibility, abdominal radiography using a 3-way view is indicated.