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Quantification of Plasmid-Mediated Antibiotic Resistance in an Experimental Evolution Approach
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Multidrug-resistant Shigella sonnei carrying the plasmid-mediated mcr-1 gene in China

Qiuxia Ma1, Yong Huang2, Jian Wang3

  • 1Navy's Center for Disease Control and Prevention, Beijing, China; Institute of Disease Control and Prevention, Academy of Military Medical Sciences, Beijing, China.

International Journal of Antimicrobial Agents
|March 5, 2018
PubMed

Insights

Active mcr-1 gene conferring polymyxin resistance was found in Shigella sonnei isolates in China. These multidrug-resistant strains, identified since 2010, highlight the potential for widespread horizontal gene transfer of resistance.

Area of Science:

  • Microbiology
  • Genetics
  • Public Health

Background:

  • The plasmid-mediated polymyxin resistance gene, mcr-1, has been reported globally in various bacteria.
  • Previously, only one instance of an inactivated mcr-1 gene in Shigella sonnei was documented worldwide.
  • China has been a focal point for the initial emergence and spread of mcr-1.

Purpose of the Study:

  • To screen historical Shigella sonnei isolates in China for the presence of the mcr-1 gene.
  • To characterize the antimicrobial resistance profiles and genetic elements associated with mcr-1 positive S. sonnei.
  • To investigate the transferability of polymyxin resistance via plasmid conjugation.

Main Methods:

  • Screening of 1650 S. sonnei strains isolated between 2003-2015 for the mcr-1 gene.
  • Antimicrobial susceptibility testing and determination of co-harbored resistance genes.
  • Pulsed-field gel electrophoresis (PFGE), plasmid profiling, Southern blotting, and whole-plasmid sequencing.
  • Plasmid conjugation experiments to assess transferability of polymyxin resistance.

Main Results:

  • Six mcr-1 positive S. sonnei isolates exhibiting polymyxin B resistance (MICs 4-8 μg/mL) were identified from Shanghai (2010-2012).
  • Four isolates displayed multidrug resistance, co-harboring blaCTX-M-14, mph(A), and blaTEM on different plasmids.
  • mcr-1 positive plasmids shared similar IncI2 backbones with variations in insertion sequences and recombination regions.
  • Evidence suggests mcr-1 emerged in S. sonnei in China by mid-2006, with active forms present since at least 2010.

Conclusions:

  • This study reports for the first time the presence of active mcr-1 in multidrug-resistant Shigella sonnei in China.
  • The diverse mobile genetic elements on mcr-1 harboring plasmids facilitate horizontal gene transfer among Enterobacteriaceae.
  • Continuous national and international surveillance of mcr-1 positive Shigella and antibiotic resistance patterns is crucial.
Keywords:
MDRMultidrug-resistantShigella sonneimcr-1

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