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Validation of a screening method for the detection of colistin-resistant E. coli containing mcr-1 in feral swine feces

Jeffrey C Chandler·Alan B. Franklin·Sarah N. Bevins·Kevin T Bentler·Jonas Bonnedahl·Christina A. Ahlstrom·Bledar Bisha·Susan A. Shriner
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Abstract

A method was developed and validated for the detection of colistin-resistant Escherichia coli containing mcr-1 in the feces of feral swine. Following optimization of an enrichment method using EC broth supplemented with colistin (1 µg/mL) and vancomycin (8 µg/mL), aliquots derived from 100 feral swine fecal samples were spiked with of one of five different mcr-1 positive E. coli strains (between 100 and 104 CFU/g), for a total of 1,110 samples tested. Enrichments were then screened using a simple boil-prep and a previously developed real-time PCR assay for mcr-1 detection. The sensitivity of the method was determined in swine feces, with mcr-1 E. coli inoculums of 0.1-9.99 CFU/g (n = 340), 10-49.99 CFU/g (n = 170), 50-99 CFU/g (n = 255), 100-149 CFU/g (n = 60), and 200-2,200 CFU/g (n = 175), which were detected with 32%, 72%, 88%, 95%, and 98% accuracy, respectively. Uninoculated controls (n = 100) were negative for mcr-1 following enrichment.

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Jeffrey C Chandler, Alan B. Franklin, Sarah N. Bevins, Kevin T Bentler, Jonas Bonnedahl, Christina A. Ahlstrom, Bledar Bisha, Susan A. Shriner. 2020. Validation of a screening method for the detection of colistin-resistant E. coli containing mcr-1 in feral swine feces. https://doi.org/10.1016/j.mimet.2020.105892

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