Eva Smelikova1, Jan Tkadlec1, Marcela Krutova2. 1. Department of Medical Microbiology, Charles University, 2nd Faculty of Medicine and Motol University Hospital, Czech Republic. 2. Department of Medical Microbiology, Charles University, 2nd Faculty of Medicine and Motol University Hospital, Czech Republic. Electronic address: marcela.krutova@lfmotol.cuni.cz.
Abstract
BACKGROUND: Colistin belongs to the last-resort antibiotics. The discovery of plasmid-bound colistin resistance mediated by the mcr-gene(s) is of great concern because, given its biological potential, there is a risk of its rapid spread. OBJECTIVES: To discuss the current literature on the methods for the screening for mcr-mediated resistance to colistin. SOURCES: Literature was drawn from a search of PubMed from 1 January 2016 to 26 April 2021. CONTENT: The selective culture-based or culture-independent approach can be used for the screening of mcr-mediated resistance to colistin in clinical samples. Rapid Polymyxin NP, Colistin Drop or Colistin Agar Spot tests are applicable for the selection of isolates with a suspected resistance to colistin that has to be confirmed by broth microdilution. The mcr-mediated resistance to colistin can be confirmed by the detection of the causal gene(s) or by phenotype using EDTA-colistin broth disc elution; production of the MCR-1 enzyme can be confirmed with lateral flow immunoassay, using matrix-assisted laser desorption/ionization time-of flight or liquid chromatography-based mass spectrometry. Whole-genome sequencing (WGS) is the ultimate typing method. When a WGS platform is not available at a healthcare facility, a WGS-outsourced service, in combination with freely available bioinformatics tools, allows for the characterization of the mcr-gene(s) carrying isolates. IMPLICATIONS: mcr-mediated colistin resistance should be monitored through active targeted screening. The broth microdilution method is required for colistin susceptibility testing but as only a selected number of clinical isolates are tested, colistin resistance, including mcr-mediated, may remain undetected. In mcr-1-positive Escherichia coli isolates, the MIC to colistin can range from 2 to 8 mg/L, so it is proposed that Enterobacterales with a colistin MIC of 2 mg/L should also be included in the mcr-mediated colistin resistance screening and those with a confirmed mcr-genotype and/or MCR-phenotype should be considered to be colistin-resistant.
BACKGROUND: Colistin belongs to the last-resort antibiotics. The discovery of plasmid-bound colistin resistance mediated by the mcr-gene(s) is of great concern because, given its biological potential, there is a risk of its rapid spread. OBJECTIVES: To discuss the current literature on the methods for the screening for mcr-mediated resistance to colistin. SOURCES: Literature was drawn from a search of PubMed from 1 January 2016 to 26 April 2021. CONTENT: The selective culture-based or culture-independent approach can be used for the screening of mcr-mediated resistance to colistin in clinical samples. Rapid Polymyxin NP, Colistin Drop or Colistin Agar Spot tests are applicable for the selection of isolates with a suspected resistance to colistin that has to be confirmed by broth microdilution. The mcr-mediated resistance to colistin can be confirmed by the detection of the causal gene(s) or by phenotype using EDTA-colistin broth disc elution; production of the MCR-1 enzyme can be confirmed with lateral flow immunoassay, using matrix-assisted laser desorption/ionization time-of flight or liquid chromatography-based mass spectrometry. Whole-genome sequencing (WGS) is the ultimate typing method. When a WGS platform is not available at a healthcare facility, a WGS-outsourced service, in combination with freely available bioinformatics tools, allows for the characterization of the mcr-gene(s) carrying isolates. IMPLICATIONS: mcr-mediated colistin resistance should be monitored through active targeted screening. The broth microdilution method is required for colistin susceptibility testing but as only a selected number of clinical isolates are tested, colistin resistance, including mcr-mediated, may remain undetected. In mcr-1-positive Escherichia coli isolates, the MIC to colistin can range from 2 to 8 mg/L, so it is proposed that Enterobacterales with a colistin MIC of 2 mg/L should also be included in the mcr-mediated colistin resistance screening and those with a confirmed mcr-genotype and/or MCR-phenotype should be considered to be colistin-resistant.