Original Article Occurrence of bla NDM-7 within IncX3-type plasmid of Escherichia coli from India Deepjyoti Paul a , Amitabha Bhattacharjee a, * , Birson Ingti a , Nargis Alom Choudhury a , Anand Prakash Maurya a , Debadatta Dhar b , Atanu Chakravarty b a Department of Microbiology, Assam University, Silchar, India b Department of Microbiology, Silchar Medical College and Hospital, Silchar, India article info Article history: Received 5 August 2016 Received in revised form 11 December 2016 Accepted 13 December 2016 Available online xxx Keywords: Carbapenemase bla NDM-7 IncX3 Escherichia coli abstract Background: New-Delhi metallo-b-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 NDM-7 and alteration in plasmid copy number under concentration gradient carbapenem stress. Materials and methods: Six bla NDM-7 producing Escherichia coli isolates were obtained from Silchar Medical College and Hospital and the co-existence of other b-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 NDM-7 was also determined. The change in copy number of transconjugable plasmid carrying bla NDM-7 under exposure of different car- bapenem antibiotics was determined by quantitative Real Time PCR. Results: All the six isolates carrying bla NDM-7 were conjugatively transferable through an IncX3-type plasmid and were also found to co-harbor bla CTX-M-15 . Genetic analysis of bla NDM-7 showed an associa- tion of ISAba125, IS5 and a truncated portion of ISAba125 in the upstream region and ble MBL gene in the downstream region of bla NDM-7 . Complete loss of the plasmids carrying bla NDM-7 was observed between 85th to 90th serial passages when antibiotic pressure was withdrawn.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 NDM-7 encoding plasmid was highly affected by the concentration of ertapenem. Conclusion: The present study has first demonstrated presence of IncX3-type plasmid encoding bla NDM-7 within nosocomial isolates of E. coli. Measures must be taken to prevent or atleast slowdown the emergence of this resistance determinant in this country. © 2017 Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved. 1. Introduction New-Delhi metallo-b-lactamase-1 (bla NDM-1 ) was first identified from Klebsiella pneumoniae and Escherichia coli from a Swedish patient in the year 2009 and in due course many variants have evolved within diverse host [1]. This b-lactamase could hydrolyse most of the b-lactam antibiotics including carbapenems and are increasingly spreading worldwide [2]. So far a total of 15 allele types of NDM family have been reported (http://www.ncbi.nlm.nih. gov/projects/pathogens/submit-beta-lactamase) and very recently, a newly identified bla NDM variant having two amino acid substitution at position Asp-130-Asn and Met-154-Leu was re- ported and designated as bla NDM-7 which is known to have higher hydrolysis efficiency against carbapenems compared to its ancestor bla NDM-1 [2]. In addition, bla NDM-7 is often co-existed with other antibiotic resistance genes and was found to be located within conjugative plasmid which act as a vehicle for their rapid dissem- ination [3]. Though earlier study described the horizontal transfer of bla NDM-7 and its prevalence rate among enterobacteriaceae [4], there is still paucity of the data regarding their genetic context in this region which creates a missing link in the origin and evolution of this gene. Knowledge about the genetic context and plasmid copy number variation may help in assessment of risk factors and therapeutic challenges. Therefore in this study, we investigated the * Corresponding author. E-mail address: ab0404@gmail.com (A. Bhattacharjee). Contents lists available at ScienceDirect Journal of Infection and Chemotherapy journal homepage: http://www.elsevier.com/locate/jic http://dx.doi.org/10.1016/j.jiac.2016.12.009 1341-321X/© 2017 Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved. J Infect Chemother xxx (2016) 1e5 Please cite this article in press as: Paul D, et al., Occurrence of bla NDM-7 within IncX3-type plasmid of Escherichia coli from India, J Infect Chemother (2016), http://dx.doi.org/10.1016/j.jiac.2016.12.009