Teo Jeanette, Ngan Grace, Balm Michelle, Jureen Roland, Krishnan Prabha, Lin Raymond
Department of Laboratory Medicine, National University Hospital, Singapore 119074. Singapore .
Western Pac Surveill Response J. 2012 Mar 29;3(1):19-24. doi: 10.5365/WPSAR.2011.2.4.010. Print 2012 Jan.
In this study, we molecularly characterized 12 NDM-1 producing clinical Enterobacteriaceae (Klebsiella pneumoniae, Escherichia coli, Enterobacter cloacae) isolates that were part of a collection of non-carbapenem susceptible isolates obtained during a one-year period. These isolates were obtained from four local general hospitals in Singapore.
Polymerase chain reaction (PCR) assays and sequencing was used to determine the presence of β-lactamase encoding genes (bla) including bla NDM-1 and plasmid-mediated quinolone and aminoglycoside resistance determinants. Conjugation experiments were performed to determine the transferability of bla NDM-1. Isolate relatedness was determined by multilocus sequence typing (MLST).
The isolates were completely resistant to the second- and third-generation cephalosporins tested as well as carbapenems. Susceptibility profiling of the isolates indicated that 100% retained susceptibility to tigecycline while 11/12 (91.7%) were susceptible to colistin. The bla NDM-1 gene was encoded on plasmids that were easily transferable. None of the patients had a travel history to countries where NDM-1 has been reported. The isolates appear clonally unrelated with MLST, revealing a diversity of clonal types among the Klebsiella pneumoniae and Escherichia coli isolates.
The ease of NDM-1 plasmid transmissibility may help their dissemination among the Enterobacteriaceae. Although it appears that the isolates are clonally unrelated, epidemiological links cannot be fully excluded without further research.
在本研究中，我们对12株产NDM-1的临床肠杆菌科细菌（肺炎克雷伯菌、大肠埃希菌、阴沟肠杆菌）进行了分子特征分析，这些菌株是在一年时间内收集的非碳青霉烯敏感菌株集合的一部分。这些菌株来自新加坡的四家当地综合医院。
采用聚合酶链反应（PCR）检测和测序来确定β-内酰胺酶编码基因（bla）的存在，包括bla NDM-1以及质粒介导的喹诺酮和氨基糖苷类耐药决定簇。进行接合实验以确定bla NDM-1的可转移性。通过多位点序列分型（MLST）确定菌株的亲缘关系。
这些菌株对所检测的第二代和第三代头孢菌素以及碳青霉烯类药物完全耐药。菌株的药敏分析表明，100%对替加环素保持敏感，而12株中有11株（91.7%）对黏菌素敏感。bla NDM-1基因编码在易于转移的质粒上。所有患者均无前往已报告NDM-1的国家的旅行史。这些菌株经MLST分析显示克隆无关，揭示了肺炎克雷伯菌和大肠埃希菌菌株中克隆类型的多样性。
NDM-1质粒易于传播可能有助于其在肠杆菌科细菌中扩散。尽管这些菌株似乎克隆无关，但未经进一步研究不能完全排除流行病学联系。
