Characterization of the stability and dynamics of Tn6330 in an Escherichia coli strain by nanopore long reads

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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  • Ruichao Li
  • Kaichao Chen
  • Edward Wai-Chi Chan
  • Sheng Chen


Original languageEnglish
Pages (from-to)1807-1811
Journal / PublicationJournal of Antimicrobial Chemotherapy
Issue number7
Online published29 Mar 2019
Publication statusPublished - Jul 2019
Externally publishedYes


Background: The mcr-1 gene has been widely reported in both bacterial chromosomes and plasmids, while its stability in these genetic materials is not well understood. Objectives: Our aim was to characterize the stability and dynamics of Tn6330 elements in both a plasmid and the chromosome in a single bacterial population. Methods: Plasmid-borne and chromosomal Tn6330 were characterized by PCR, conjugation, S1-PFGE, stability assay, single-molecule long-read sequencing and bioinformatics analysis. Results: Tn6330 was simultaneously detected in both a plasmid and the chromosome of a clinical Escherichia coli strain. The plasmid was found to comprise the IncFIB replicon and a phage-like replicon, as well as two integrons that harboured various mobile elements and resistance genes including mcr-1, floR, blaTEM-1b and strAB. Both plasmid-borne and chromosomal Tn6330 transposons could be re-organized into a circular intermediate that played a role in transmission of the mcr-1 gene. Tn6330 was found to be very stable in both the plasmid and chromosome after 30 passages of 12 h with or without colistin selective pressure. The decayed structure of Tn6330 in the genuine single DNA molecules of bacterial populations, although occurring at a very low frequency, could be detected for the first time, in which Tn6330 was degraded into a single ISApl1 element. Conclusions: Long-read sequencing technology is a good tool to study the evolution and stability of genetic elements in bacteria. The ultrastability of an mcr-1-encoding element in a bacterial plasmid and chromosome renders it unlikely to be eradicated quickly by the reduced use of colistin, and factors leading to the frequent demise of Tn6330 warrant further studies.