Table 2. Dilution ranges and susceptibility breakpoints used in the antimicrobial susceptibility test of Streptococcus uberis isolated from CM.
| Antimicrobial | MIC dilution range (μg/mL) | CLSI breakpoints (μg/mL)1 |
|---|---|---|
| Ampicillin2 | 0.12–8.0 | 0.25 |
| Ceftiofur3 | 0.5–4.0 | 2.0 |
| Cephalothin2 | 2.0–16.0 | 8.0 |
| Erythromycin2 | 0.25–4.0 | 0.25 |
| Penicillin2 | 0.12–8.0 | 0.12 |
| Penicillin+novobiocin3 | 1.0/2.0–8.0/16.0 | 1.0/2.0 |
| Pirlimycin3 | 0.5–4.0 | 2.0 |
| Tetracycline2 | 1.0–8.0 | 2.0 |
1Susceptibility breakpoints according to the guidelines of CLSI [33]. Isolates with minimum inhibitory concentrations less than or equal to the stated breakpoints were considered as susceptible to the antimicrobial.
2Human-derived susceptibility breakpoints. As no breakpoints were available for Strep. uberis recovered from bovine mastitis in the CLSI guidelines, the susceptibility to these antimicrobials was based on breakpoints of viridans group streptococci or Streptococcus spp.
3Susceptibility breakpoints based on bovine mastitis data.