TABLE 1

Overview of the plasmids, resistance genes, and colistin MICs of the mcr-1-positive Escherichia coli strains isolated in Switzerland included in this study

E. coli strainSourcegSTaCollection periodAntibiotic resistancebColistin MIC (μg/ml)cPlasmiddPlasmidic resistance gene(s)emcr-1 location (plasmid length in kb)
100RHuman feces (traveler)102015CST, PMB, LVX, CIP, DOX, SXT≥8IncHI2aadA1, aadA2, blaTEM-1, mcr-1, mph(A), sul3, tetA, dfrA15, dfrA14IncHI2 (256)
IncFII/FIBblaTEM-1, aadA2, aadA24, aph(3)-Ia, qnrS1, cmlA1, sul3, tetA, dfrA12
IncX1
ColRNAI
19-M12Human feces (traveler)52015CST, PMB, DOX, SXT≥8IncHI2aadA2, blaTEM-1, mcr-1, mph(A), cmlA1, sul3, tetA, dfrA12, dfrA14IncHI2 (232)
IncFII/FIBblaTEM-1, aadA1, qnrS1, tetA, dfrA1
31349Human feces (HIV+ subject)52015CST, PMB≥8IncX4mcr-1.2IncX4 (33)
IncL/M
IncFII
IncFIB
Mcp0271Retail chicken meat582016CST, AMP4IncX4mcr-1IncX4 (33)
IncFII/FIB/FIAblaTEM-1
Mcp0221Retail chicken meat17752016CST4IncI2mcr-1IncI2 (65)
Mbl488Retail chicken meat382014CST, SMX, TMP, NAL, CAZ, CTX, AMP, TET8IncK2blaTEM-1, mcr-1, sul2IncK2 (101)
IncFII/FIBaadA1, blaTEM-1, sul1, tetA, dfrA1
IncI1aadA5, blaCTX-M-1, sul2, dfrA17
po111
Mbl536Retail chicken meat2262014CST, SMX, TMP, CIP, TET, NAL, AMP4IncK2blaTEM-1, mcr-1, sul2IncK2 (101)
IncI1blaTEM-1, sul2, tetA, dfrA1
IncX1blaTEM-52
Mbl323Retail chicken meat382014CST, CAZ, AMP, NAL, CTX8IncK2blaCMY-2Chromosome
IncNaadA22, lnuF
IncFII/FIBColRNAI
Mbl506fRetail chicken meat10492014CST, TET, NAL, CTX, CHL, SMX, TMP, CAZ, AMP8IncFII/FIBtetAChromosomei
IncI1aadA1, erm(42)
IncI2aad24, blaTEM-1
IncQ1haad24, strA, strB, mph(B), sul1, sul2, tetA, dfrA1h
  • a Sequence type (ST) based on multilocus sequence typing was determined with MLSTtool.

  • b Only antibiotics with a nonsusceptible phenotype according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria, except for TET, SMX, DOX, and minocycline for which Clinical and Laboratory Standards Institute (CLSI) criteria were used (20, 21). CST, colistin; PMB, polymyxin B; LVX, levofloxacin; CIP, ciprofloxacin; DOX, doxycycline; SXT, trimethoprim-sulfamethoxazole; SMX, sulfamethoxazole; AMP, ampicillin; CAZ, ceftazidime; TMP, trimethoprim; TET, tetracycline; CTX, cefotaxime; NAL, nalidixic acid; CHL, chloramphenicol.

  • c MIC values were obtained with microdilution Trek Diagnostic Systems panels GNX2F for human strains or EUVSEC panels for chicken meat strains; the two panels analyze different MIC ranges for colistin (0.25 to 4 μg/ml and 1 to 16 μg/ml, respectively).

  • d Incompatibility groups were determined with PlasmidFinder.

  • e Resistance genes were determined with ResFinder.

  • f Strain harboring a chromosomally integrated blaCTX-M-32.

  • g Retail chicken meat was imported from Germany.

  • h Integrated into the chromosome based on whole-genome sequencing.

  • i Two mcr-1 copies in different loci.