Prevalence of Moraxella catarrhalis in the nasopharyngeal specimen from 1082 hospitalized children with respiratory infection and the drug resistance of the isolates
TANG Ping1, SHI Wei3, ZENG Hai-Ling1, DING Wei2, WANG Cheng2, YAO Kai-Hu3, WEN De-Nian2
Department of Laboratory Medicine, People's Hospital of Zhongjiang County, Zhongjiang, Sichuan 618100, China
Abstract：Objective To investigate the prevalence of Moraxella catarrhalis in the nasopharyngeal region of children with respiratory infection and the sensitivity of Moraxella catarrhalis isolates to common antimicrobial drugs. Methods Nasopharyngeal swabs were collected from 1082 children with respiratory infection, and Moraxella catarrhalis strains were isolated. The E-test method and disc diffusion test were used to determine the sensitivity of these strains to 11 common antimicrobial drugs. The test results were interpreted with reference to the standards of European Committee on Antimicrobial Susceptibility Testing (EUCAST), Clinical and Laboratory Standards Institute (CLSI), and British Society for Antimicrobial Chemotherapy (BSAC). The nitrocefin disc method was used to detect whether the isolated strains produced β-lactamase. Results Among the 1 082 children with respiratory infection, 77 (77/1082, 7.12%) carried Moraxella catarrhalis in the nasopharyngeal region. All the strains produced β-lactamase. With reference to all the three standards, all the strains were sensitive to amoxycillin-clavulanate and had a susceptibility rate of >95% towards ciprofloxacin and tetracycline. According to the EUCAST and CLSI standards, the susceptibility rate of the strains towards sulfamethoxazole-trimethoprim was as high as 98.7%, and more than 80% of all strains were sensitive to the three cephalosporins detected; however, with reference to the BSAC standard, only 2.6% of the strains were sensitive to cefuroxime, with an intermediate rate of 44.2% and a drug resistance rate of 53.2%. The rate of resistance to ampicillin was 81.8%. According to the CLSI standard, the non-susceptibility rate of the strains to erythromycin was 79.2%, and according to the EUCAST or BSAC standards, their non-susceptibility rate reached 90.9%; more than one third of the strains (27/77, 35.1%) had a minimal inhibitory concentration of >256 mg/L. Conclusions All of the Moraxella catarrhalis isolates in the nasopharyngeal region of children with respiratory infection produce β-lactamase and are sensitive to amoxycillin-clavulanate. These isolates have high susceptibility rates to the third- and fourth-generation cephalosporins and sulfamethoxazole-trimethoprim, but most of the isolates are resistant to ampicillin, cefuroxime, and erythromycin.
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