Purpose: The emergence and spread of carbapenem-resistant Enterobacteriaceae  deserves special concern worldwide. Unlike the epidemiological characteristics reported in other studies, we found that the production of New Delhi metallo-β-lactamase 5 was the main mechanism for the resistance of Escherichia coli  to carbapenems.
Methods: All carbapenem-resistant strains were collected from July 2017 to July 2018 of the First Affiliated Hospital of Nanjing Medical University. The presence of carbapenemase-encoding genes was detected using PCR and gene sequencing. Genetic relatedness of the bla _NDM-5-positive E. coli  strains was determined with PFGE and MLST. Susceptibility profiles were measured with broth microdilution method and E-test strips. Transferability features of bla _NDM-5 gene were assessed by conjugation experiments, S1-PFGE, southern blotting and PCR-based replicon typing methods. The genetic structures surrounding bla _NDM-5 were acquired by whole genome sequencing and PCR mapping.
Results: Among the 28 carbapenem-resistant E. coli  strains, 18 (64%) were verified as NDM-5 producers. The 18 bla _NDM-5-positive E. coli  strains showed high resistance to most antibiotics, but 100% were sensitive to colistin and tigecycline. In addition, the 18 bla _NDM-5-positive E. coli  strains belonged to eight STs, among which ST167, ST410 and ST101 were found to cause clonal spread in the hospital. Further studies found that the bla _NDM-5 gene was located on an IncX3-type plasmid, and all plasmids harbored an IS3000-Δ ISAba125 -IS5-bla _NDM-5-ble  MBL-trpF-dsbC -IS26  structure.
Conclusion: The clonal spread of bla _NDM-5-positive E. coli  strains and horizontal dissemination via the pNDM-MGR 194-like plasmids should draw more attention. Appropriate infection control operations should be performed to prevent the further spread of bla _NDM-5.
Keywords: Escherichia coli , carbapenem-resistant Enterobacteriaceae , New Delhi metallo-β-lactamase, bla _NDM-5, IncX3 type plasmid