Gentamicin susceptibility in Escherichia coli related to the genetic background: problems with breakpoints.
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 (> or =16 mg/L).
Jakobsen
L
L
National Center for Antimicrobials & Infection Control, Statens Serum Institut, Copenhagen, Denmark. lja@ssi.dk
Sandvang
D
D
Jensen
V F
VF
Seyfarth
A M
AM
Frimodt-Møller
N
N
Hammerum
A M
AM
D000123:Acetyltransferases / Q000235:genetics; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics; D005839:Gentamicins / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods
D000900:Anti-Bacterial Agents; D005839:Gentamicins; D000123:Acetyltransferases; C045539:aminoglycoside N(3')-acetyltransferase