What is the significance of Moraxella catarrhalis in a sputum culture?

From the Guidelines

Moraxella catarrhalis in a sputum culture typically indicates a respiratory tract infection that requires antibiotic treatment, with amoxicillin-clavulanate (Augmentin) 875/125 mg twice daily for 5-7 days being the recommended first-line treatment. This recommendation is based on the fact that over 90% of M. catarrhalis strains produce beta-lactamase, making them resistant to plain amoxicillin or penicillin 1. The clavulanate component in amoxicillin-clavulanate is necessary to inhibit this beta-lactamase activity. Alternative options include doxycycline 100 mg twice daily, trimethoprim-sulfamethoxazole (Bactrim DS) one tablet twice daily, or a respiratory fluoroquinolone like levofloxacin 750 mg daily if the patient has allergies or other contraindications to first-line therapy.

Key Considerations

• The susceptibility of M. catarrhalis to antibiotics has changed little since 1999, with all isolates being resistant to amoxicillin, ampicillin, piperacillin, and penicillin due to beta-lactamase production 1.
• Amoxicillin-clavulanate remains effective against M. catarrhalis due to the beta-lactamase inhibiting properties of clavulanate.
• Rates of resistance to trimethoprim-sulfamethoxazole (TMP-SMX) can be as high as 50% in some cases, making it a less reliable option 1.
• Patients with underlying lung disease, such as COPD, are at increased risk of exacerbations due to M. catarrhalis and should be treated promptly.

Treatment Approach

• Initiate antibiotic treatment promptly, especially in patients with underlying lung disease.
• Monitor for clinical improvement within 48-72 hours of starting appropriate antibiotics.
• Consider supportive measures such as adequate hydration, rest, and possibly bronchodilators depending on the patient's symptoms.
• If the patient fails to improve or worsens despite appropriate therapy, consider reevaluation for possible complications or co-infections.

From the Research

Moraxella catarrhalis in Sputum Culture

• Moraxella catarrhalis is a bacterium that can be found in the upper respiratory tract and can cause infections such as acute otitis media, sinusitis, and pneumonia 2.
• It is a common cause of respiratory tract infections, along with Haemophilus influenzae and Streptococcus pneumoniae 2.
• The bacterium can produce beta-lactamase, making it resistant to certain antibiotics such as ampicillin, but it is still susceptible to other antibiotics like amoxicillin/clavulanic acid, cefuroxime, and erythromycin 2, 3.

Antibiotic Susceptibility

• Studies have shown that Moraxella catarrhalis is susceptible to various antibiotics, including amoxicillin-clavulanate, doxycycline, clarithromycin, levofloxacin, and trimethoprimsulfamethoxazole 3.
• Cefuroxime has been shown to be effective against Moraxella catarrhalis, with a sensitivity rate of 99.15% 3.
• The minimum inhibitory concentrations (MICs) of cefuroxime for Moraxella catarrhalis have been found to be in the high end of the sensitive range 3.

Interpretation of Gram-Stained Sputa

• The interpretation of gram-stained sputa containing Moraxella catarrhalis can be affected by the decolorizer solution and exposure time used 4.
• Optimal results can be obtained with acetone alone after 10 seconds or with a 1:1 mixture of acetone and ethanol after 20 seconds 4.
• Inadequate decolorization of Moraxella catarrhalis in sputa can lead to underreporting of this organism 4.

Pathogenesis and Colonization

• Moraxella catarrhalis is a human respiratory tract pathogen that can cause otitis media in infants and children, as well as exacerbations of chronic obstructive pulmonary disease in adults 5, 6.
• The prevalence of colonization of the upper respiratory tract is high in infants and children, but decreases substantially in adulthood 6.
• Most strains of Moraxella catarrhalis produce beta-lactamase, making them resistant to certain antibiotics 6.