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Quantification of Plasmid-Mediated Antibiotic Resistance in an Experimental Evolution Approach
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A Novel Phenotypic Method To Screen for Plasmid-Mediated Colistin Resistance among Enterobacteriales

Drew T Bell1, Yehudit Bergman2, Abida Q Kazmi2

  • 1Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.

Journal of Clinical Microbiology
|March 8, 2019
PubMed

Insights

A new test using EDTA can detect plasmid-mediated colistin resistance (PMCR) by observing reduced colistin MIC. This method shows high sensitivity and specificity for identifying mcr genes in Enterobacteriales.

Area of Science:

  • Microbiology
  • Antimicrobial Resistance
  • Molecular Biology

Background:

  • Plasmid-mediated colistin resistance (PMCR) mediated by mcr genes poses a significant public health threat due to rapid spread among pathogens.
  • MCR enzymes, crucial for colistin resistance, have been recently identified to require zinc for their activity.

Purpose of the Study:

  • To develop and evaluate a modified colistin broth-disk elution (CBDE) test incorporating EDTA to screen for PMCR.
  • To assess the diagnostic performance of the EDTA-CBDE method in detecting mcr genes in Enterobacteriales isolates.

Main Methods:

  • Modification of the standard CBDE test by including EDTA to inhibit zinc-dependent MCR enzymes.
  • Testing 85 Enterobacteriales isolates, including 12 mcr-positive strains, using the EDTA-CBDE assay.
  • Comparison of EDTA-CBDE results with molecular genotyping for sensitivity and specificity determination.

Main Results:

  • The EDTA-CBDE method demonstrated 100% sensitivity and 95.8% specificity in detecting PMCR compared to molecular methods.
  • The presence of EDTA significantly reduced the minimum inhibitory concentration (MIC) of colistin in the presence of MCR enzymes.
  • The assay effectively screened for plasmid-mediated colistin resistance in the tested isolates.

Conclusions:

  • The EDTA-modified CBDE test is a sensitive and specific method for screening plasmid-mediated colistin resistance.
  • This assay provides a valuable tool for the rapid detection of mcr genes in clinical settings.
  • Isolates testing positive via the EDTA-CBDE method warrant further molecular confirmation of mcr gene presence.
Keywords:
colistinmcrphenotypic methodplasmid-mediated colistin resistance

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