Complete sequencing of an IncX3 plasmid carrying blaNDM-5 allele reveals an early stage in the dissemination of the blaNDM gene

Purpose: The aim of the present study was to perform molecular characterisation of the bla(NDM) plasmids and to understand the mechanism of its spread among pathogenic bacteria. Materials and Methods: Seventy-six non-repetitive carbapenem-resistant isolates which were collected during Nov 2011 to April 2013 from four hospitals in Chennai were analyzed for the presence of the bla(NDM) gene by PCR. Further, the genetic context of the bla(NDM) gene was analyzed by PCR specific to ISAba125 and ble(MBL) gene. One of the bla(NDM) plasmid was completely sequenced in the Illumina HiSeq platform. Results: Twenty-three isolates consisting of 8 Escherichia coli, 8 Klebsiella pneumoniae, 3 Klebsiella oxytoca, 3 Acinetobacter baumanii and 1 Pseudomonas aeruginosa were found to carry the bla(NDM) gene. In 18 isolates the bla(NDM) gene was associated with a ble(MBL) gene and the ISAba125 element. The complete sequencing of pNDM-MGR194 revealed an IncX3 replication type plasmid, with a length of 46,253 bp, an average GC content of 47% and 59 putative ORFs. The iteron region contained the bla(NDM5) gene and the ble(MBL), trpF and dsbC genes downstream and an IS5 inserted within the ISAba125 element upstream. Conclusion: This is the first report where the bla(NDM) gene insertion in a plasmid is not accompanied by other resistance gene determinants. These observations suggest that the IncX3 plasmid pNDM-MGR194 is an early stage in the dissemination of the bla(NDM).