Nasopharyngeal colonization of Moraxella catarrhalis in young korean children

Background: Nasopharyngeal bacterial flora can cause respiratory tract diseases as well as invasive bacterial diseases. Moraxella catarrhalis colonizing in the nasopharynx is considered an important potential pathogen with an increasing production of β-lactamase. This study examined the nasopharyngeal colonization rate of M. catarrhalis and the antibiotic susceptibility of M. catarrhalis. Materials and Methods: Healthy children who visited one of the three University hospitals in the Republic of Korea or attended a day-care center around the participating hospitals were enrolled in this study. The nasopharyngeal samples were obtained by nasopharyngeal washing with normal saline and M. catarrhalis was isolated. The nasopharyngeal colonization rate of M. catarrhalis was investigated and the minimal inhibitory concentrations (MICs) were measured for commonly used oral antibiotics (amoxicillin, amoxicillin/clavulanate, cefaclor, cefixime, cefdinir, cefditoren, erythromycin and trimethoprim). Results: Three hundred and seventy-nine children aged between 6 months and 5 years were enrolled, and the nasopharyngeal colonization rate of M. catarrhalis was 33% (124 children). All isolated M. catarrhalis produced β-lactamase. The MIC₉₀ of the antibiotics were as follows: amoxicillin, >16 mg/L; amoxicillin/clavulanate, 0.5 mg/L; cefaclor, 8 mg/L; cefixime, 0.125 mg/L; cefdinir, 0.25 mg/L; cefditoren, 0.25 mg/L; erythromycin, 0.5 mg/L; and trimethoprim, >16 mg/L. Conclusions: M. catarrhalis was colonized in 33% of the children aged 6 months to 5 years, and showed low MICs for amoxicillin/clavulanate and oral 2^nd and 3^rd generation cephalosporins.