Acquired carbapenemases in Enterobactericeae in Singapore, 1996-2012

Aims:To characterise carbapenemase-producing Enterobacteriaceae (CRE) isolated in Singapore.Methods:Carbapenemase genes and their flanking regions were amplified and sequenced by PCR. Isolates were typed by pulsed-field gel electrophoresis and multi-locus sequence typing. Plasmids bearing carbapenemase genes were sized by S1 nuclease digestion, Southern blotting, and DNA hybridisation with appropriate probes. Transfer of these plasmids was attempted by conjugation and transformation. Successfully transferred plasmids were characterised by polymerase chain reaction (PCR) replicon typing and restriction digestion.Results:Isolates of Klebsiella pneumoniae, Escherichia coli, Enterobacter cloacae and Citrobacter species carried a variety of carbapenemase genes including bla(IMP-1), bla(IMP-4), bla(NDM-1), bla(NDM-7), bla(OXA-181), bla(OXA-48) and bla(KPC-2). Apart from K. pneumoniae with bla(OXA-181), and some K. pneumoniae with bla(NDM-1), the other isolates were not clonal. However there appears to be some spread of plasmids with bla(IMP-1), bla(NDM-1,)bla(KPC-2), and bla(OXA-48).Conclusions:The number of isolates of CRE has increased in Singapore, especially since 2010. There is a diversity of carbapenemase types that reflects the geographical proximity of other countries with CRE.