TABLE 1.
In vitro susceptibilities of 195 E. coli strains isolated from diarrheic calves to cephalosporins and quinolones
| Antimicrobial agenta | MIC (μg/ml)b
|
No. (%) resistant strains | ||
|---|---|---|---|---|
| Range | 50% | 90% | ||
| Cephalothin (≥32) | 1–>512 | 8 | 32 | 32 (16.4) |
| Cefuroxime (≥32) | 0.125–64 | 4 | 8 | 4 (2.1) |
| Cefotaxime (≥64) | ≤0.0625–2 | ≤0.0625 | 0.125 | 0 (0) |
| Cefquinome | ≤0.0625–2 | ≤0.0625 | 0.125 | |
| Nalidixic acid (≥32) | 0.5–>512 | 4 | >512 | 35 (17.9) |
| Oxolinic acid | ≤0.0625–>512 | 0.250 | 64 | |
| Enoxacin (≥8) | ≤0.0625–256 | 0.125 | 16 | 24 (12.3) |
| Enrofloxacin (≥2) | ≤0.0625–64 | ≤0.0625 | 4 | 23 (11.8) |
| Danofloxacin | ≤0.0625–64 | ≤0.0625 | 4 | |
a
Numbers in parentheses are the MIC breakpoints (in micrograms per milliliter) indicating susceptibility according to the recommendations of NCCLS (27, 28). None of the listed breakpoints are specific for the treatment of calves with diarrhea caused by E. coli. For antimicrobial agents without breakpoints, the NCCLS guidelines do not contain recommended breakpoints, and thus the percentages of resistant strains were not calculated.
b
50% and 90%, MICs at which 50 and 90% of the tested strains are inhibited, respectively.