Molecular epidemiology and analysis on resistant mechanisms of macrolide-nonsusceptible Moraxella catarrhalis

Abstract

Objective To analyze the molecular epidemiology and resistant mechanisms of macrolide-nonsusceptible Moraxella catarrhalis. Methods A total of 383 strains of Moraxella catarrhalis were collected from nasopharynx of children under 2 years old.The minimum inhibition concentration (MIC) values were determined by Etest method, and the production of β-lactamase was examined by using a nitrocefin-based test.The pulsed-field gel electrophoresis (PFGE) method was used to analyze the type of different isolates.Polymerase chain reaction (PCR) and sequencing were performed for the resistance mechanism of macrolide resistance in Moraxella catarrhalis.The non-susceptibility rates of six cities(Beijing, Shanghai, Jinan, Nanjing, Wuhan and Dongguan) were compared by χ2 test. Results According to Clinical and Laboratory Standards Institute(CLSI) breakpoints, the non-susceptibility rates for erythromycin and azithromycin in 383 strains of Moraxella catarrhalis were 40% and 23%, respectively.Whereas, the non-susceptibility rates were 59% and 60% based on pharmacokinetics/pharmacodynamics (PK/PD) breakpoints.Significant differences in non-susceptibility rates to macrolide were observed in different cities, and the higher non-susceptibility rates were determined in relatively northern cities, such as Beijing and Jinan.Among the 383 strains of Moraxella catarrhalis, 92%(353/383) of isolates produced β-lactamase.A total of 14 patterns of groups were generated by PFGE in 37 high-level macrolide resistant Moraxella catarrhalis, and 43%(16/37) of isolates could be considered to be related or indistinguishable to group A.In this study, the ermA, ermB, mefA, and mefE genes were not detected, while the A2982T, A2796T, A2983T mutations in 23S rRNA gene may be related to macrolide resistance in Moraxella catarrhalis.The A2982T and A2796T mutations conferred high-level macrolide resistance, while the A2983T mutation conferred low-level resistance. Conclusions A large number of macrolide-nonsusceptible Moraxella catarrhalis isolates are detected in the study.The macrolide resistance is probably related to the mutations in 23S rRNA gene, and the relationship between MIC values of macrolide and mutations has been determined.（Chin J Lab Med,2012,35:247-252） Key words: Macrolides; Moraxella(branhamella) catarrhalis; Drug resistance，bacterial; RNA，ribosomal，23S; Mutation