Abstract
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. 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). 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. 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.
Highlights
The isolates appear clonally unrelated with multilocus sequence typing (MLST), revealing a diversity of clonal types among the Klebsiella pneumoniae and Escherichia coli isolates
The ease of New Delhi metallo- -lactamase-1 (NDM-1) plasmid transmissibility may help their dissemination among the Enterobacteriaceae
It appears that the isolates are clonally unrelated, epidemiological links cannot be fully excluded without further research
Summary
Polymerase chain reaction (PCR) assays and sequencing was used to determine the presence of β-lactamase encoding genes (bla) including bla NDM-1. Conjugation experiments were performed and plasmid-mediated quinolone to determine the transferability of and aminoglycoside resistance blaNDM-1. The 52 isolates comprised the following species: 31 Klebsiella pneumoniae, 13 Escherichia coli, seven Enterobacter cloacae and one Enterobacter aerogenes. Two of these isolates (594 and 693) were obtained from the same patient but from different collection sites (Table 1). The identification and initial susceptibility testing of the isolates was performed with VITEK 2 automated system (bioMérieux Vitek, Inc., Hazelwood, MO, USA). The Etest MBL (bioMérieux, Marcy l’Etoile, France) was used for the phenotypic detection of metallo- -lactamases
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