TABLE 3.
Broth microdilution resistance breakpoint (μg/mL), MIC50 and MIC90 values, and percentage resistant of 48 Mannheimia haemolytica isolates collected at the arrival (n = 26) and 10 to 14 days later at revaccination (n = 22)
| Antimicrobial | Timepoint | Resistant breakpoint (μg/mL) | MIC50 (μg/mL) | MIC90 (μg/mL) | % resistant |
|---|---|---|---|---|---|
| FLOR | Arrival | ≥8.0 | 0.5 | 1 | 0 |
| Revacc | 4 | ≥8 | 40.9% | ||
| CEF | Arrival | ≥8.0 | ≤0.25 | ≤0.25 | 0 |
| Revacc | ≤0.25 | ≤0.25 | 0 | ||
| PEN | Arrival | ≥1.0 | 0.5 | 0.5 | 7.7% |
| Revacc | ≥8 | ≥8 | 86.3% | ||
| OXY | Arrival | ≥8.0 | ≤0.5 | ≤0.5 | 3.8% |
| Revacc | ≥8 | ≥8 | 100% | ||
| ENR | Arrival | ≥2.0 | ≤0.12 | ≤0.12 | 0 |
| Revacc | ≥2 | ≥2 | 100% | ||
| DAN | Arrival | ≥1.0 | ≤0.12 | ≤0.12 | 0 |
| Revacc | ≥1 | ≥1 | 100% | ||
| TIL | Arrival | ≥32.0 | 8 | 16 | 3.8% |
| Revacc | ≥64 | ≥64 | 100% | ||
| TUL | Arrival | ≥64.0 | 4 | 8 | 0 |
| Revacc | ≥64 | ≥64 | 95.5% |
Abbreviations: CEF, ceftiofur; DAN, danofloxacin; ENR, enrofloxacin; FLOR, florfenicol; OXY, oxytetracycline; PEN, penicillin; TIL, tilmicosin; TUL, tulathromycin.