Purpose: The aim of the present study was to perform molecular characterisation of the blaNDM 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 blaNDM gene by PCR. Further, the genetic context of the blaNDM gene was analyzed by PCR specific to ISAba125 and bleMBL gene. One of the blaNDM 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 blaNDM gene. In 18 isolates the blaNDM gene was associated with a bleMBL 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 blaNDM5 gene and the bleMBL , trpF and dsbC genes downstream and an IS5 inserted within the ISAba125 element upstream.
Conclusion: This is the first report where the blaNDM 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 blaNDM .