The expected number of breakpoints was set to 1 (default setting) and several 2-point reductions (Base TSP+MLE, Extended TSP+MLE, 2-point LOD distance) [ 27] were solved using the LKH heuristic methods [ 28].
As previously described, the Lambda and breakpoint per chromosome settings were set to 6.75 and 100, respectively (Jong et al, 2004; de Leeuw et al, 2004).
The selection criteria for mecA screening were set to include all isolates exceeding the oxacillin resistance breakpoint, and in addition, to include a representative number other isolates, especially those having an oxacillin MIC near the breakpoint.
The drug concentrations (breakpoints) were set as follows: piperacillin, 64 mg/l; imipenem and meropenem, 8 mg/l; aztreonam and ceftazidime, 16 mg/l; amikacin, tobramycin and arbekacin, 4 mg/l; ciprofloxacin and colistin, 2 mg/l.
Susceptible (S) breakpoints were set as MIC ≤8 μg/mL for fluconazole, ≤0.125 μg/mL for itraconazole, <1 μg/mL for voriconazole and ≤ 1 μg/mL for amphotericin B, respectively.
The EUCAST breakpoints for ofloxacin (0.125/4 mg/L) have been set to ensure that the wild type is reported intermediate, indicating the need for high dosage to treat infections with wild type isolates, and any isolates with raised MICs are considered resistant.
Based on PK/PD considerations, the EUCAST breakpoints for cefaclor (0.032/0.5 mg/L) have been set to ensure that the wild type is reported intermediate, indicating the need for high dosage to treat infections with wild type isolates, and any isolates with raised MICs are considered resistant.
The term 'intermediate' susceptibility was avoided given its use in other bacterial infections for which standard breakpoints are set based on large-scale consensus [ 16].
The breakpoints for resistance were set according to the NCCLS (penicillin, R ≥ 0.25 μg/ml; oxacillin, R ≥ 0.5 μg/ml; erythromycin, R ≥ 8.0 μg/ml; gentamicin, R ≥ 16 μg/ml; clindamycin, R ≥ 4.0 μg/ml; ciprofloxacin, R ≥ 4.0 μg/ml; and vancomycin, R ≥ 32 μg/ml).
Breakpoints should be set prior to an antibacterial being used clinically or at the time of an approved use.
