Table 3. Recommendations given by EUCAST and CLSI for the six antibiotics examined in the present study.
| Guideline | EUCAST MIC breakpoint (mg/L) | EUCAST Zone diameter breakpoint (mm) * | CLSI interpretive criteria MIC (mg/L) ** | ||||
|---|---|---|---|---|---|---|---|
| Antibiotic | S ≤ | R > | S ≥ | R < | S ≤ | I | R ≥ |
| Benzylpenicillin1 / penicillin2 | 0.125 | 0.125 | 21 | 21 | 0.12 | 0.25-2 | 4 |
| Cefotaxime | NR | NR | NR | NR | 1 | 2 | 4 |
| Meropenem | 0.25 | 0.25 | 31 | 31 | 0.5 | NR | NR |
| Vancomycin | 1 | 1 | 16 | 16 | 1 | NR | NR |
| Linezolid | NR | NR | NR | NR | 2 | NR | NR |
| Rifampicin | 0.125 | 0.125 | 25 | 25 | NR | NR | NR |
S, Susceptible. I, Intermediate. R, Resistant. NR, No recommendation. 1 Benzylpenicillin for EUCAST testing. 2 Penicillin for CLSI testing. Quality control strain Streptococcus pneumoniae ATCC 49619 for both EUCAST and CLSI. * Susceptibility recommendation method: Medium: Mueller-Hinton (MH) plates with 5% defibrinated horse blood and 20 mg/L β-NAD (MH-F). Inoculum: McFarland 0.5. Incubation: 5% CO2, 35±1 °C, 18±2h. Isolates with insufficient growth after 16-20 h incubation were re-incubated immediately and inhibition zones and MICs read after a total of 40-44 h incubation. Reading: Read zone edges as the point showing no growth viewed from the front of the plate with the lid removed and with reflected light. ** Susceptibility recommendation method: Medium: Cation-adjusted Mueller-Hinton broth (CAMHB) supplemented with 2.5% lysed horse blood (CAMHB-LHB). Inoculum: Direct colony suspension, equivalent to a 0.5 McFarland standard. Incubation: 35 °C, 5% CO2, 20-24 h.