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

Abstract

In total, 120 Escherichia coli isolates positive for one of the gentamicin resistance (GENR) 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 8-64mg/L, whereas isolates positive for aac(3)-II had MICs of 32 to >512mg/L, suggesting a relationship between the distribution of MICs and the specific GENR mechanism. The MIC distribution, regardless of the GENR mechanism, was 8 - >512mg/L, which supports the clinical breakpoint of MIC>4mg/L suggested by EUCAST and questions the breakpoint recommended by the CLSI (≥16mg/L). © 2007 The Authors Journal Compilation © 2007 European Society of Clinical Microbiology and Infectious Diseases.