Department of Laboratory Medicine, The First Affiliated Hospital of Chongqing Medical University, Chongqing 400016, China.
Infect Genet Evol. 2013 Mar;14:1-7. doi: 10.1016/j.meegid.2012.10.010. Epub 2012 Dec 7.
Carbapenem-resistant Enterobacteriaceae, including strains from multiple species harboring metallo-β-lactamases (IMP, NDM or VIM) and non-metallo (KPC) carbapenemases, as well as those combining an extended-spectrum β-lactamase (ESBL) enzyme with porin loss, present an increasingly urgent clinical danger. The aim of this study was to characterize the carbapenemases and ESBLs in carbapenem-non-susceptible (CNS) Enterobacter cloacae (E. cloacae) isolates from a Chinese teaching hospital. A total of 986 non-duplicated E. cloacae isolates collected between September 2009 and February 2012 were analyzed via antimicrobial susceptibility testing. Carbapenemase and ESBL genes were examined using PCR amplification and DNA sequencing. Clonal relatedness was investigated by pulsed-field gel electrophoresis (PFGE) and dendrogram analysis. We demonstrated that CNSs were prevalent (35/986, 3.55%) in E. cloacae. Phenotypes of carbapenemases and ESBLs were respectively found in 9 (25.7%) and 23 (65.7%) of the 35 CNS E. cloacae strains. KPC-2, IMP-8, IMP-26, NDM-1, TEM-6, CTX-M-3', CTX-M-14' and SHV-12 type β-lactamases were identified in 3 (8.6%), 5 (14.3%), 1 (2.9%), 1 (2.9%), 13 (37.1%), 9 (25.7%), 8 (22.9%) and 9 (25.7%) isolates, respectively. Importantly, multiple resistance genes were found to be co-expressed in the same CNS E. cloacae isolates. PFGE and dendrogram analysis showed clonal diversity among these isolates. Our study suggested that over-production of carbapenemases and ESBLs contributed together to the CNS of E. cloacae in China. Furthermore, the decreased susceptibility to carbapenems in E. cloaca in the hospital might arise via stepwise accumulations of multiple drug-resistance determinants in different clones. The prevalence of CNS E. cloacae isolates was not caused by clonal dissemination. Most importantly, we identified a CNS E. cloacae isolate co-expressing IMP-26 and NDM-1, which is the first reported to the best of our knowledge. This is also the first report of NDM-1-producing Enterobacteriaceae in mainland China.
耐碳青霉烯肠杆菌科细菌，包括携带金属β-内酰胺酶（IMP、NDM 或 VIM）和非金属（KPC）碳青霉烯酶的多种菌株，以及同时携带超广谱β-内酰胺酶（ESBL）酶和孔蛋白缺失的菌株，构成了日益紧迫的临床威胁。本研究旨在对中国一所教学医院分离的耐碳青霉烯阴沟肠杆菌（E. cloacae）的碳青霉烯酶和 ESBL 进行特征描述。对 2009 年 9 月至 2012 年 2 月间收集的 986 份非重复阴沟肠杆菌进行了药敏试验分析。采用 PCR 扩增和 DNA 测序检测碳青霉烯酶和 ESBL 基因。通过脉冲场凝胶电泳（PFGE）和聚类分析检测克隆相关性。结果表明，35/986（3.55%）阴沟肠杆菌为耐碳青霉烯肠杆菌。在 35 株耐碳青霉烯阴沟肠杆菌中，分别发现 9 株（25.7%）存在碳青霉烯酶表型，23 株（65.7%）存在 ESBL 表型。鉴定出 3 株（8.6%）携带 KPC-2、5 株（14.3%）携带 IMP-8、1 株（2.9%）携带 IMP-26、1 株（2.9%）携带 NDM-1、13 株（37.1%）携带 TEM-6、9 株（25.7%）携带 CTX-M-3'、8 株（22.9%）携带 CTX-M-14'和 9 株（25.7%）携带 SHV-12 型β-内酰胺酶。重要的是，同一株耐碳青霉烯阴沟肠杆菌中发现了多种耐药基因的共表达。PFGE 和聚类分析显示这些分离株存在克隆多样性。本研究表明，碳青霉烯酶和 ESBLs 的过度表达共同导致了中国阴沟肠杆菌的耐碳青霉烯现象。此外，医院阴沟肠杆菌对碳青霉烯类药物的敏感性降低可能是由于不同克隆中逐步累积了多种耐药决定因素。耐碳青霉烯阴沟肠杆菌分离株的流行并非由克隆传播引起。值得注意的是，我们鉴定出一株同时携带 IMP-26 和 NDM-1 的耐碳青霉烯阴沟肠杆菌，这是我们所知的首例报道。这也是中国大陆首次报告携带 NDM-1 的肠杆菌科细菌。
