Gentamicin susceptibility in Escherichia coli related to the genetic background: problems with breakpoints

L. Jakobsen, D. Sandvang, Vibeke Frøkjær Jensen, Anne Mette Seyfarth, N. Frimødt-Møller, Anette Marie Hammerum

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In total, 120 Escherichia coli isolates positive for one of the gentamicin resistance (GEN(R)) genes aac(3)-II, aac(3)-IV or ant(2 '')-I were tested for gentamicin susceptibility by the agar dilution method. Isolates positive for aac(3)-IV or ant(2 '')-I had an MIC distribution of 8-64 mg/L, whereas isolates positive for aac(3)-II had MICs of 32 to > 512 mg/L, suggesting a relationship between the distribution of MICs and the specific GEN(R) mechanism. The MIC distribution, regardless of the GEN(R) mechanism, was 8 - > 512 mg/L, which supports the clinical breakpoint of MIC > 4 mg/L suggested by EUCAST and questions the breakpoint recommended by the CLSI (>= 16 mg/L).
Original languageEnglish
JournalClinical Microbiology and Infection
Issue number8
Pages (from-to)830-832
Publication statusPublished - 2007


  • gentamicin
  • susceptibility tests
  • resistance genes
  • MIC distribution
  • Escherichia coli
  • breakpoints

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