Occurrence of bla within IncX3-type plasmid of Escherichia coli from India.

Background: New-Delhi metallo-β-lactamase-7 with higher hydrolytic activity than its ancestor NDM-1 is emerging across the globe including India. In this study, we have investigated the genetic context of bla and alteration in plasmid copy number under concentration gradient carbapenem stress.

Materials And Methods: Six bla producing Escherichia coli isolates were obtained from Silchar Medical College and Hospital and the co-existence of other β-lactamases and transferability of this resistant determinant was determined by transformation and conjugation assay followed by typing of the plasmid by PBRT method. Genetic context and plasmid stability of bla was also determined. The change in copy number of transconjugable plasmid carrying bla under exposure of different carbapenem antibiotics was determined by quantitative Real Time PCR.

Results: All the six isolates carrying bla were conjugatively transferable through an IncX3-type plasmid and were also found to co-harbor bla. Genetic analysis of bla showed an association of ISAba125, IS5 and a truncated portion of ISAba125 in the upstream region and ble gene in the downstream region of bla. Complete loss of the plasmids carrying bla was observed between 85th to 90th serial passages when antibiotic pressure was withdrawn. After analyzing the relative copy number it was observed that the copy number of the bla encoding plasmid was highly affected by the concentration of ertapenem.

Conclusion: The present study has first demonstrated presence of IncX3-type plasmid encoding bla within nosocomial isolates of E. coli. Measures must be taken to prevent or atleast slowdown the emergence of this resistance determinant in this country.