Objective To investigate the prevalence of colistin resistance and mcr-1 gene in pa-tients with bloodstream infection caused by Escherichia coli (E.coli) and Klebsiella pneumoniae (K.pneu-moniae) in Zhejiang Province. Methods A total of 869 clinical strains of the Enterobacteriaceae family, including 611 E.coli and 258 K.pneumonia strains, were isolated from patients with bloodstream infection (BSI) in Zhejiang Province from March 2014 to April 2015. Broth microdilution method and PCR were re-spectively performed to detect colistin resistance and mcr-1 gene in those stains. Susceptibilities of mcr-1-positive strains to other antibiotics were assessed by E-test. Pulsed-field gel electrophoresis(PFGE) and multilocus sequence typing(MLST) were used for molecular typing. Location of mcr-1 gene was determined by analysis of PFGE profiles of S1-digested genomic DNA and Southern blot hybridization. Plasmid transfer to E.coli recipients was investigated using filter mating test. Clinical data of the patients infected with mcr-1-positive strains was collected and analyzed. Results The minimum inhibitory concentration (MIC) values of colistin to the 869 Enterobacteriaceae strains ranged from ≤0.06 μg/ml to 16 μg/ml. Six (0.69%) E.coli strains were identified to be colistin-resistant and mcr-1-positive and the MIC values against them ranged from 8 μg/ml to 16 μg/ml. No colistin-resistant or mcr-1-positive K.pneumonia strain was identified. All mcr-1-positive strains were susceptible to carbapenems and most of them(83.33%,5/6) were suscepti-ble to tigecycline and β-lactamase inhibitor combinations tested in this study. The six mcr-1-positive strains were of different sequence types (STs) and the mcr-1 genes carried by them located on three types of plas-mids with the sizes of 33 kb,61 kb and 244.4 kb. Conclusion The prevalence of mcr-1 gene in E.coli and K.pneumonia strains isolated from patients with BSI in Zhejiang Province was relatively low, only ac-counting for 0.69% of all isolated Enterobacteriaceae strains.Those strains carrying mcr-1 gene showed low drug resistance to colistin. The mcr-1-positive strains were usually non-pathogenic clones and remained sus-ceptible to many antimicrobial agents, which was conducive to favorable outcomes. In order to clarify the clinical impact of this novel resistance gene on public health,further studies should be conducted.%目的 研究浙江省大肠埃希菌和肺炎克雷伯菌引起的血流感染患者中多粘菌素耐药情况及mcr-1基因流行情况.方法 从2014年3月至2015年4月,收集来自浙江省11个市23家医院引起血流感染的大肠埃希菌(611株)和肺炎克雷伯菌(258株)共869株.微量肉汤稀释法和E-test法分别检测多粘菌素及其他抗菌药物的最低抑菌浓度(MIC);PCR法检测多粘菌素耐药基因mcr-1及mcr-1阳性菌株的其他耐药基因;脉冲场凝胶电泳(PFGE)和多位点序列分型(MLST)分析阳性菌株的亲缘关系;S1-PFGE联合Southern印迹杂交定位mcr-1基因.结果 共发现6株多粘菌素耐药大肠埃希菌(3株MIC为8 μg/ml,3株MIC为16 μg/ml),且6株菌株均为mcr-1阳性,耐药率及mcr-1检出率为0.69%;未发现多粘菌素耐药或mcr-1阳性肺炎克雷伯菌.PFGE结果显示6株菌株均为非同源性,MLST结果显示6株菌株均为不同的ST型.Southern印迹杂交表明mcr-1基因分别定位在约33 kb、61 kb和244.4 kb不同大小质粒上.结论 mcr-1在浙江省血流感染患者中流行率低,仅为0.69%,且介导低水平的多粘菌素耐药(MIC 为8 ~16 μg/ml).mcr-1阳性大肠埃希菌通常为非ST131型克隆,同时对其他多种类型抗生素敏感,且并不影响感染患者的预后.需要进行更深入的研究来探明mcr-1基因在临床上的地位.
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