Dongeun Yong,^1,2 Mark A. Toleman,² Christian G. Giske,³ Hyun S. Cho,⁴ Kristina Sundman,⁵ Kyungwon Lee,¹ and Timothy R. Walsh^2*

Yonsei University College of Medicine, Research Institute of Antimicrobial Resistance, Seoul, Republic of Korea,¹ Department of Medical Microbiology, Cardiff University, Cardiff, United Kingdom,² Clinical Microbiology, MTC?Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden,³ Yonsei University College of Life Science and Biotechnology, Seoul, Republic of Korea,⁴ Department of Clinical Microbiology, Orebro University Hospital, Orebro, Sweden⁵

Received 10 June 2009/ Returned for modification 7 August 2009/ Accepted 10 September 2009

A Swedish patient of Indian origin traveled to New Delhi, India, and acquired a urinary tract infection caused by a carbapenem-resistant Klebsiella pneumoniae strain that typed to the sequence type 14 complex. The isolate, Klebsiella pneumoniae 05-506, was shown to possess a metallo-β-lactamase (MBL) but was negative for previously known MBL genes. Gene libraries and amplification of class 1 integrons revealed three resistance-conferring regions; the first contained bla_CMY-4 flanked by ISEcP1 and blc. The second region of 4.8 kb contained a complex class 1 integron with the gene cassettes arr-2, a new erythromycin esterase gene; ereC; aadA1; and cmlA7. An intact ISCR1 element was shown to be downstream from the qac/sul genes. The third region consisted of a new MBL gene, designated bla_NDM-1, flanked on one side by K. pneumoniae DNA and a truncated IS26 element on its other side. The last two regions lie adjacent to one another, and all three regions are found on a 180-kb region that is easily transferable to recipient strains and that confers resistance to all antibiotics except fluoroquinolones and colistin. NDM-1 shares very little identity with other MBLs, with the most similar MBLs being VIM-1/VIM-2, with which it has only 32.4% identity. As well as possessing unique residues near the active site, NDM-1 also has an additional insert between positions 162 and 166 not present in other MBLs. NDM-1 has a molecular mass of 28 kDa, is monomeric, and can hydrolyze all β-lactams except aztreonam. Compared to VIM-2, NDM-1 displays tighter binding to most cephalosporins, in particular, cefuroxime, cefotaxime, and cephalothin (cefalotin), and also to the penicillins. NDM-1 does not bind to the carbapenems as tightly as IMP-1 or VIM-2 and turns over the carbapenems at a rate similar to that of VIM-2. In addition to K. pneumoniae 05-506, bla_NDM-1 was found on a 140-kb plasmid in an Escherichia coli strain isolated from the patient's feces, inferring the possibility of in vivo conjugation. The broad resistance carried on these plasmids is a further worrying development for India, which already has high levels of antibiotic resistance.

* Corresponding author. Mailing address: Department of Medical Microbiology, School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, United Kingdom. Phone: 44 (0)1453 811744. Fax: 44 (0)2920 742161.