title: Molecular characterization of NDM-1 producing Enterobacteriaceae isolates in Singapore hospitals.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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).
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Laboratory Medicine, National University Hospital, Singapore 119074. Singapore .
authors.forename: Jeanette
authors.initials: J
authors.lastname: Teo
authors.forename: Grace
authors.initials: G
authors.lastname: Ngan
authors.forename: Michelle
authors.initials: M
authors.lastname: Balm
authors.forename: Roland
authors.initials: R
authors.lastname: Jureen
authors.forename: Prabha
authors.initials: P
authors.lastname: Krishnan
authors.forename: Raymond
authors.initials: R
authors.lastname: Lin
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