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J Antimicrob Chemother. 2019 Feb 28. pii: dkz044. doi: 10.1093/jac/dkz044. [Epub ahead of print]

Antimicrobial resistance-encoding plasmid clusters with heterogeneous MDR regions driven by IS26 in a single Escherichia coli isolate.

Author information

1
College of Animal Science and Veterinary Medicine, Henan Agricultural University, Zhengzhou, China.
2
West China Hospital, Sichuan University, Chengdu, China.

Abstract

BACKGROUND:

IS26-flanked transposons played an increasingly important part in the mobilization and development of resistance determinants. Heterogeneous resistance-encoding plasmid clusters with polymorphic MDR regions (MRRs) conferred by IS26 in an individual Escherichia coli isolate have not yet been detected.

OBJECTIVES:

To characterize the complete sequence of a novel blaCTX-M-65- and fosA3-carrying IncZ-7 plasmid with dynamic MRRs from an E. coli isolate, and to depict the mechanism underlying the spread of resistance determinants and genetic polymorphisms.

METHODS:

The molecular characterization of a strain carrying blaCTX-M-65 and fosA3 was analysed by antimicrobial susceptibility testing and MLST. The transferability of a plasmid bearing blaCTX-M-65 and fosA3 was determined by conjugation assays, and the complete structure of the plasmid was obtained by Illumina, PacBio and conventional PCR mapping, respectively. The circular forms derived from IS26-flanked transposons were detected by reverse PCR and sequencing.

RESULTS:

A novel IncZ-7 plasmid pEC013 (∼118 kb) harbouring the blaCTX-M-65 and fosA3 genes was recovered from E. coli isolate EC013 belonging to D-ST117. The plasmid was found to have heterogeneous and dynamic MRRs in an individual strain and the IS26-flanked composite transposon-derived circular intermediates were identified and characterized in pEC013.

CONCLUSIONS:

The heterogeneous MRRs suggested that a single plasmid may actually be a cluster of plasmids with the same backbone but varied MRRs, reflecting the plasmid's heterogeneity and the survival benefits of having a response to antimicrobial-related threatening conditions in an individual strain.

PMID:
30820562
DOI:
10.1093/jac/dkz044

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