Determination of breakpoint concentrations by meropenem titration (0.025, 0.075, 1, 2, 4, 8, 16, and 32 μg/ml) for five different K. pneumoniae strains. Etest-derived MICs are given in the legend for each strain. The gray bar indicates the concentration of 8 μg/ml used for the analysis of the clinical isolates. The susceptibility/resistance threshold used for the analysis of the clinical isolates is indicated by the dashed line.