TABLE 3.
Antimicrobials, breakpoint values for resistance, and frequency of resistance in 231 bovine, 82 ovine, and 60 caprine S. aureus mastitis isolates from Norway
| Antimicrobial | Breakpoint (μg/ml) | No. (%) of resistant isolates |
|||
|---|---|---|---|---|---|
| Bovine | Ovine | Caprine | All | ||
| Cephalothin | ≥32 | 0 | 0 | 0 | 0 |
| Chloramphenicol | ≥32 | 0 | 0 | 0 | 0 |
| Clindamycin | ≥4 | 0 | 0 | 0 | 0 |
| Enrofloxacin | ≥4 | 0 | 0 | 0 | 0 |
| Erythromycin | ≥8 | 0 | 0 | 0 | 0 |
| Fusidic acid | ≥1 | 2 (0.9) | 0 | 0 | 2 (0.5) |
| Gentamicin | ≥16 | 0 | 0 | 0 | 0 |
| Oxacillin | ≥4 | 0 | 0 | 0 | 0 |
| Penicillina | ≥0.25 | 6 (2.6) | 2 (2.4) | 3 (5.0) | 11 (2.9) |
| Streptomycin | ≥32 | 5 (2.2) | 1 (1.2) | 3 (5.0) | 9 (2.4) |
| Sulfadiazin | ≥512 | 1 (0.4) | 0 | 0 | 1 (0.3) |
| Oxytetracycline | ≥16 | 1 (0.4) | 1 (1.2) | 0 | 2 (0.5) |
| Trimethoprim | ≥8 | 1 (0.4) | 1 (1.2) | 0 | 2 (0.5) |
a
β-Lactamase production of all isolates was determined. All β-lactamase-positive isolates had a MIC of >0.125 μg/ml, and all β-lactamase-negative isolates had a MIC of ≤0.125 μg/ml.