Table 3. MIC50 and MIC90 range and resistance frequencies of 30 bovine Clostridium difficile isolates to 4 antimicrobial drugs by E-test on Muller-Hinton agar after 48 h of incubation*.
| Drug | MIC50, μg/mL | MIC90, μg/mL | Range, μg/mL | Resistant isolates, % (no. resistant/no. tested), MIC (μg/mL) | Overrepresented PCR ribotypes (no.) |
|---|---|---|---|---|---|
| Vancomycin | 0.5 | 0.75 | 0.25–1.5 | 0 | 0 |
| Metronidazole | 0.38 | 0.75 | 0.125–2.0 | 0 | 0 |
| Levofloxacin | 32 | 32 | 4 to >32 | 73 (22/30), >32 | B89 (9/9), C129 (2/2), D189 (4/4), other 3 ribotypes (7 isolates) |
| Clindamycin | 16.0 | >256 | 6 to >256 | 73 (22/30), >12; 37 (11/30), >256 | B89 (9/9), C129 (2/2) |
*The breakpoints used were vancomycin susceptible, <4.0 μg/mL; vancomycin resistant, >32.0 μg/mL; metronidazole susceptible, <8.0 μg/mL; metronidazole resistant, >32.0 μg/mL; clindamycin susceptible, <2.0 μg/mL; clindamycin resistant >8.0 μg/mL; levofloxacin susceptible, <2.0 μg/mL; levofloxacin resistant, >8.0 μg/mL.