Detection of NDM-7 in Germany, a new variant of the New Delhi metallo-β-lactamase with increased carbapenemase activity

This study characterized a new variant of the New Delhi metallo-β-lactamase (NDM). A multidrug-resistant Escherichia coli isolate was recovered from the wounds, throat and rectum of a Yemeni patient who presented at the Frankfurt University Hospital in Germany. The presence of β-lactamase genes was analysed by PCR and sequencing. The isolate was further characterized by susceptibility testing, conjugation and transformation assays and plasmid analysis. The E. coli isolate was resistant to all β-lactams including carbapenems. By PCR analysis, the β-lactamase genes blaCMY-2, blaCTX-M-15, blaTEM-1 and blaNDM were identified. Sequencing revealed a blaNDM gene that differed from blaNDM-1 by two point mutations at positions 388 (G→A) and 460 (A→C) corresponding to amino acid substitutions Asp130Asn and Met154Leu, respectively. This NDM variant was identified as NDM-7. The blaNDM-7 gene was located on a self-transferable IncX3 plasmid of 60 kb. E. coli TOP10 transformants harbouring NDM-7 showed higher MICs of β-lactams including carbapenems compared with transformants harbouring NDM-1. Multilocus sequence typing analysis revealed that the E. coli isolate belonged to a novel sequence type (ST599). This study identified a novel NDM variant in E. coli, NDM-7, possessing a high ability to hydrolyse β-lactam antibiotics. Given the diversity of NDM variants located on self-transferable plasmids found in different Gram-negative species and isolated in different countries, the blaNDM gene will most likely efficiently disseminate worldwide.