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. 2012 Mar 29;3(1):19-24.
doi: 10.5365/WPSAR.2011.2.4.010. Print 2012 Jan.

Molecular characterization of NDM-1 producing Enterobacteriaceae isolates in Singapore hospitals

Jeanette Teo  1 , Grace Ngan, Michelle Balm, Roland Jureen, Prabha Krishnan, Raymond Lin
Affiliations

Molecular characterization of NDM-1 producing Enterobacteriaceae isolates in Singapore hospitals

Jeanette Teo et al. Western Pac Surveill Response J. .

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.

Conclusion: 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.

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Figures

Fig. 1
Fig. 1
Typical agarose gel (0.7%) analysis of the plasmid content of clinical isolates and their transconjugants
See this image and copyright information in PMC

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