What is the role of M catarrhalis in the pathogenesis of acute otitis media (AOM)?

Updated: Sep 25, 2019
  • Author: John D Donaldson, MD, FRCSC, FACS; Chief Editor: Arlen D Meyers, MD, MBA  more...
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In the mid-1970s, M catarrhalis was classified as nonpathogenic in middle ear infections, even though under its previous name, Neisseria catarrhalis, it constituted approximately 10% of all isolates from middle ear aspirates. At that time, M catarrhalis was almost universally susceptible to ampicillin-type penicillins. After 20 years and 2 name changes (from N catarrhalis to Branhamella catarrhalis to M catarrhalis), it is isolated in up to a quarter of children with AOM, and resistance to the ampicillin-type beta-lactams is almost universal.

M catarrhalis is a gram-negative diplococcus and is considered part of the normal flora of the human upper respiratory tract. Resistance is conferred by the secretion of multiple isoenzymes of lactamase, which may be plasmid or chromosomal in origin and which may be inducible (ie, present only in low levels until a substrate is provided). More than 1 isoenzyme may be secreted by a single bacterium.

At present, almost all forms are blocked by clavulanic acid, and most are still susceptible to sulfonamides, lactamase-stable cephalosporins, or broad-spectrum macrolides. M catarrhalis is often found to coexist with other airway pathogens. The lactamases (cephalosporinases) that M catarrhalis secretes may protect those other bacteria from antimicrobial agents to which the second target pathogen might ordinarily be susceptible.

A study by Chonmaitree et al of 367 infants (followed for 286 child-years) indicated that bacterial-viral interactions are associated with AOM, with such interactions between M catarrhalis and various respiratory viruses having been found in the report to affect the risk of upper respiratory tract infection and AOM. [14]

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