大环内酯类不敏感卡他莫拉菌的分子流行病学特点及耐药机制

Abstract

目的 研究大环内酯类不敏感卡他莫拉菌的分子流行病学特点及耐药机制.方法 从2岁以下健康婴幼儿鼻咽部共分离出383株卡他莫拉菌,利用Etest法测定383株卡他莫拉菌对大环内酯类的最低抑菌浓度( MIC)；采用头孢硝噻吩色原法测定β内酰胺酶的产生情况；利用脉冲场凝胶电泳(PFGE)对菌株分型；通过聚合酶链反应(PCR)及序列分析对大环内酯类耐药机制进行研究；采用X2检验对6个城市(北京、上海、济南、南京、武汉、东莞)卡他莫拉菌对抗菌药物的不敏感率进行分析比较.结果 按照美国临床和实验室标准化协会( CLSI)判定折点,383株卡他莫拉菌对红霉素和阿奇霉素的不敏感率分别为40％和23％；按照药物代谢动力学/药物效应动力学(PK/PD)判定折点,其对红霉素和阿奇霉素的不敏感率分别为59％和60％.不同城市间卡他莫拉菌对大环内酯类的不敏感率存在显著差别,相对靠北部城市如北京和济南,其不敏感率明显高于相对靠南部城市(P＜0.05).在383株卡他莫拉菌中,有92％( 353/383)的菌株β内酰胺酶阳性；用PFGE方法将选取的37株高耐大环内酯类(MIC ＞256 mg/L)卡他莫拉菌分为14个型,其中有43％ (16/37)的菌株被认为与A型相关.但未发现ermA、ermB、mefA及mefE等耐药基因.在23S rRNA中,A2982T、A2796T及A2983T等突变位点与大环内酯类耐药可能有关.其中A2982T和A2796T突变可能主要介导高水平耐药,A2983T突变可能介导低水平耐药.结论 本研究发现大量大环内酯类不敏感的卡他莫拉菌；其耐药机制可能与23S rRNA位点发生突变有关,且突变位点与大环内酯类的MIC值存在一定关系.

Objective To analyze the molecular epidemiology and resistant mechanisms ofmacrolide-nonsusceptible Moraxella catarrhalis.Methods A total of 383 strains of Moraxella camrrhaliswere 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 anitrocefin-based test.The pulsed-field gel electrophoresis (PFGE) method was used to analyze the type ofdifferent isolates.Polymerase chain reaction (PCR) and sequencing were performed for the resistancemechanism of macrolide resistance in Moraxella catarrhalis.The non-susceptibility rates of six cities( Beijing,Shanghai,Jinan,Nanjing,Wuhan and Dongguan) were compared byx2 test.Results According to Clinicaland Laboratory Standards Institute (CLSI) breakpoints,the non-susceptibility rates for erythromycin andazithromycin in 383 strdns 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 andJinan.Among the 383 strains of Moraxella catarrhalis,92％ (353/383) of isolates produced β-lactamase.Atotal 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 merE 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.