The aim of this study was to compare CLSI and EUCAST MIC and disk diffusion 
carbapenem breakpoints for the detection of carbapenemase-producing Klebsiella 
pneumoniae. K. pneumoniae strains with known KPC (n = 31) or VIM (n = 20) 
carbapenemases were characterized by disk diffusion (Oxoid) and Etest 
(bioMérieux) vs. imipenem, meropenem and ertapenem, and with VITEK2 (bioMérieux, 
five different cards). Extended-spectrum β-lactamase (ESBL) testing was 
performed with VITEK2 (bioMérieux), ESBL combination disks (Becton Dickinson) 
and the ESBL Etest (bioMérieux). With CLSI and EUCAST MIC breakpoints, 
respectively, 11 and seven of the strains were susceptible to imipenem, 12 and 
eight to meropenem, and seven and none to ertapenem. The EUCAST epidemiological 
cut-off (ECOFF) values for meropenem and ertapenem identified all carbapenemase 
producers, whereas the imipenem ECOFF failed in five strains. All carbapenemase 
producers were detected with EUCAST disk diffusion breakpoints for ertapenem and 
meropenem, and four strains were susceptible to imipenem. CLSI disk diffusion 
breakpoints characterized 18 (imipenem), 14 (meropenem) and three (ertapenem) 
isolates as susceptible. When cards with a single carbapenem were used, 
detection failures with VITEK2 were four for imipenem, none for meropenem and 
one for ertapenem. Cards containing all three carbapenems had one to two 
failures. With ESBL combination disks, 21/31 KPC producers and 2/20 VIM 
producers were positive. With VITEK2, no VIM producers and between none and 
seven KPC producers were ESBL-positive. All carbapenemase producers were 
detected with the meropenem MIC ECOFF, or the clinical EUCAST breakpoint for 
ertapenem. EUCAST disk diffusion breakpoints for meropenem and ertapenem 
detected all carbapenemase producers. VITEK2 had between none and four failures 
in detecting carbapenemase producers, depending on the antibiotic card.