Dissemination of blaNDM-5 gene via an IncX3-type plasmid among non-clonal Escherichia coli in China

Background: The emergence and spread of New Delhi metallo-beta-lactamase-producing Enterobacteriaceae has been a serious challenge to manage in the clinic due to its rapid dissemination of multi-drug resistance worldwide. As one main type of carbapenemases, New Delhi metallo-beta-lactamase (NDM)is able to confer resistance to almost all beta-lactams, including carbapenems, in Enterobacteriaceae. Recently, New Delhi metallo-beta-lactamase-5 attracted extensive attention because of increased resistance to carbapenems and widespread dissemination. However, the dissemination mechanism of bla(NDM-5) gene remains unclear. Methods: A total of 224 carbapenem-resistant Enterobacteriaceae isolates (CRE) were collected from different hospitals in Zhejiang province. NDM-5-positive isolates were identified and subjected to genotyping, susceptibility testing, and clinical data analysis. We established the genetic location of bla(NDM-5) with southern blot hybridisation, and analysed plasmids containing bla(NDM-5 )with filter mating and DNA sequencing. Results: Eleven New Delhi metallo-beta-lactamase-5 (NDM-5)-producing strains were identified, including 9 Escherichia coil strains, 1 Klebsiella pneumoniae strain, and 1 Citrobacter freundii strain. No epidemiological links for E coil isolates were identified by multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). S1-PFGE and southern blot suggested that the bla(NDM-5) gene was located on a 46-kb IncX3-type plasmid in all isolates. Nine of the 11 isolates (81.8%) tested could successfully transfer their carbapenem-resistant phenotype to E. coil strain C600. Moreover, sequence analysis further showed that this plasmid possessed high sequence similarity to most of previously reported bla(NDM-5)-habouring plasmids in China. Conclusion: The present data in this study showed the IncX3 type plasmid played an important role in the dissemination of bla(NDM-5) in Enterobacteriaceae. In addition, to the best of our knowledge, this report is the first to isolate both E coil and C freundii strains carrying bla(NDM-5) from one single patient, which further indicated the possibility of bla(NDM-5) transmission among diverse species. Close surveillance is urgently needed to monitor the further dissemination of NDM-5-producing isolates.