TABLE 4.
Antimicrobials, breakpoint criteria, and frequency of resistance in 212 S. aureus isolates collected from Canadian dairy herds in three provinces
| Antimicrobial agent | Breakpoint (μg/ml) | No. of isolatesa in:
|
Total no.
|
||||||
|---|---|---|---|---|---|---|---|---|---|
| Ontario
|
PEI
|
Quebec
|
|||||||
| No. | % | No. | % | No. | % | No. | % | ||
| Tilmicosin | ≥32 | 2 | 2.1 | - | - | - | - | 2 | 0.9 |
| Penicillin | ≥0.25 | 12 | 12.5 | - | - | 9 | 8.6 | 21 | 9.9 |
| Erythromycin | ≥8 | 3 | 3.1 | - | - | - | - | 3 | 1.4 |
| Oxacillin plus 2% NaCl | ≥4 | 1 | 1.0 | 1 | 9.1 | - | - | 2 | 0.9 |
| Pirlimycin | ≥4 | 5 | 5.2 | - | - | - | - | 5 | 2.4 |
| Penicillin-novobiocin | ≥4/8 | - | - | - | - | - | - | - | - |
| Tetracycline | ≥16 | 1 | 1.0 | - | - | 2 | 1.9 | 3 | 1.4 |
| Cephalothin | ≥32 | - | - | - | - | - | - | - | - |
| Ceftiofur | ≥8 | - | - | - | - | - | - | - | - |
| Sulfadimethoxine | ≥512 | 5 | 5.2 | 1 | 9.1 | 10 | 9.5 | 16 | 7.5 |
| Resistant to none | 67 | 69.8 | 9 | 81.8 | 84 | 80.0 | 160 | 75.5 | |
| Total | 96 | 100.0 | 11 | 100.0 | 105 | 100.0 | 212 | 100.0 | |
a
A dash (-) indicates no isolates resistant to a given antimicrobial agent were isolated in this region.