Identification and molecular characterisation of New Delhi metallo-β-lactamase-1 (NDM-1)- and NDM-6-producing Enterobacteriaceae from New Zealand hospitals

Abstract

The global spread of New Delhi metallo-β-lactamase (NDM) is of significant public health concern. This study sought to determine whether blaNDM was present in Enterobacteriaceae isolates displaying resistance to carbapenems that were submitted to the National Antibiotic Reference Laboratory, Institute of Environmental Science and Research (Porirua, New Zealand) during 2009 and 2010. Isolates were tested for the presence of β-lactamase genes and 16S rRNA methylase genes by polymerase chain reaction (PCR) and sequencing. Plasmid transfer studies were undertaken on isolates found to be harbouring blaNDM. Molecular typing was performed by multilocus sequence typing (MLST). The blaNDM-1 gene was identified in four Enterobacteriaceae isolates (two Escherichia coli, one Klebsiella pneumoniae and one Proteus mirabilis) from four patients in New Zealand hospitals in 2009 and 2010. In addition, the blaNDM-6 gene, which differed from blaNDM-1 by a point mutation at position 698 (C→T), was also identified in an E. coli isolate from the same patient who harboured the blaNDM-1-positive P. mirabilis. All four patients had recently been hospitalised or received health care in India. Four of the isolates also produced a CTX-M-15 extended-spectrum β-lactamase and/or plasmid-mediated AmpC β-lactamase, and all five isolates harboured the plasmid-mediated 16S rRNA methylase rmtC gene. The E. coli types were diverse by MLST, and the K. pneumoniae isolate belonged to the internationally disseminated sequence type 11 (ST11) clone. These findings further illustrate the diversity of phenotypic and genotypic features found in association with blaNDM, in addition to documenting the international spread of this resistance mechanism, notably into a country with historically low rates of antimicrobial resistance.