Table 1.
The MICs of M. haemolytica isolated from the nasopharynx of feedlot cattlea
| Antibiotic (concentrations tested, μg/mL) | Isolate | ||||
|---|---|---|---|---|---|
| 32A | 32B | 32C | 50A | 55A | |
| Ampicillin (0.25, 0.5, 1, 2, 4, 8, 16*) | 0.25 | 0.25 | 0.25 | 0.25 | >16 |
| Ceftiofur (0.25, 0.5, 1, 2, 4, 8b) | 0.25 | 0.25 | 0.25 | 0.25 | 0.5 |
| Chlortetracycline (0.5, 1, 2, 4, 8) | 4 | 4 | 2 | 2 | 2 |
| Clindamycin (0.25, 0.5, 1, 2, 4, 8, 16) | 16 | 16 | 16 | 16 | 16 |
| Danofloxacin (0.12, 0.25b, 0.5, 1) | 0.12 | 0.12 | 0.12 | 0.12 | 0.12 |
| Enrofloxacin (0.12, 0.25, 0.5, 1, 2b) | 0.12 | 0.12 | 0.12 | 0.12 | 0.12 |
| Florfenicol (0.25, 0.5, 1, 2, 4, 8b) | 1 | 1 | 1 | 1 | 0.5 |
| Gentamycin (1, 2, 4, 8, 16) | 2 | 2 | 2 | 2 | 2 |
| Neomycin (4, 8, 16, 32*) | >32 | >32 | >32 | >32 | >32 |
| Oxytetracycline (0.5, 1, 2, 4, 8b) | >8 | >8 | >8 | >8 | >8 |
| Penicillin (0.12, 0.25, 0.5, 1, 2, 4, 8*) | 0.12 | 0.12 | 0.25 | 0.25 | >8 |
| Spectinomycin (8, 16, 32, 64) | 32 | 32 | 32 | 32 | 32 |
| Tiamulin (0.5, 1, 2, 4, 8, 16, 32) | 32 | 32 | 32 | 32 | 16 |
| Tilmicosin (4, 8, 16, 32b, 64) | 64 | 64 | 64 | >64 | >64 |
| Tulathromycin (1, 2, 4, 8, 16, 32, 64b) | 64 | 64 | 64 | 64 | 64 |
| Tylosin tartrate 0.5, 1, 2, 4, 8, 16, 32) | >32 | >32 | >32 | >32 | >32 |
a
Isolates were first screened for reduced tulathromycin susceptibility by culturing onto BHI plates supplemented with tulathromycin (2 μg/mL).
b
Breakpoints defining resistance (CLSI, 2008).
*
Resistance breakpoint defined by authors.