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Fastidiosos

Moraxella catarrhalis

Gram-negative diplococci

Identification & Growth

Identification

  • Oxidase-positive, DNase-positive, does not ferment sugars
  • Colony can be pushed intact across the plate with a loop (hockey-puck sign)

Growth Conditions

  • Blood and chocolate agar, 35 °C, 24 h; dry, opaque colonies

Clinical Significance

  • Otitis media, sinusitis, COPD exacerbation

Intrinsic Resistance

  • Trimethoprim, clindamycin, vancomycin, linezolid

Bench Alerts

  • Nearly 100% produce a BRO beta-lactamase — ampicillin/amoxicillin alone will fail
  • Amoxicillin-clavulanate, a macrolide, or an oral cephalosporin are the treatment options

Clinical Notes

Clinical presentations

  • Causes acute otitis media and sinusitis in children, frequently as part of polymicrobial infection with pneumococcus and H. influenzae.
  • Is a common cause of chronic obstructive pulmonary disease exacerbation and bronchitis in adults with underlying lung disease.
  • Bacteremia and invasive pneumonia occur rarely, more often in immunocompromised or institutionalized elderly patients.

Specimens and collection

  • Sputum or tracheal aspirate are the usual specimens for investigating respiratory exacerbation.
  • Middle ear fluid obtained by tympanocentesis may be considered in recurrent or refractory otitis media.
  • Differentiation from normal oropharyngeal flora is necessary when interpreting upper airway culture.

Epidemiology and at-risk populations

  • Frequently colonizes the nasopharynx of young children, serving as a reservoir for subsequent respiratory infection.
  • COPD patients and smokers have higher colonization and exacerbation rates from this organism.

Resistance and therapeutic implications

  • The vast majority of isolates produce beta-lactamase, conferring resistance to ampicillin and amoxicillin alone.
  • Beta-lactamase inhibitor combinations (amoxicillin-clavulanate) or oral cephalosporins are generally effective.
  • Macrolides and trimethoprim-sulfamethoxazole are alternatives in beta-lactam-allergic patients.

Bench and reporting notes

  • Gram-negative diplococci with a 'coffee bean' appearance and positive oxidase test aid presumptive identification.
  • Beta-lactamase testing should be performed routinely to guide initial therapeutic choice.
  • Growth on chocolate agar with colonies that slide intact across the agar surface ('hockey puck sign') is characteristic.

Sources

Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.

FAQ: Frequently Asked Questions

How to identify Moraxella catarrhalis in the lab?

Moraxella catarrhalis is identified through oxidase-positive, dnase-positive, does not ferment sugars, colony can be pushed intact across the plate with a loop (hockey-puck sign).

What are the intrinsic resistances of Moraxella catarrhalis?

This organism is naturally resistant to trimethoprim, clindamycin, vancomycin, linezolid. These drugs should not be reported as susceptible.

Where is Moraxella catarrhalis commonly found?

It is typically associated with otitis media, sinusitis, copd exacerbation.

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