Table 1.
In vitro susceptibilities of 403 isolates of C. difficile to fidaxomicin, rifaximin, and 10 other antimicrobial agents
| Agent | MIC (μg/ml)a |
No. (%) of isolates |
|||
|---|---|---|---|---|---|
| Range | 50% | 90% | Susceptible | Resistant | |
| Fidaxomicin | ≤0.015–0.5 | 0.12 | 0.25 | ||
| Rifaximin | ≤0.015–>128 | ≤0.015 | >128 | ||
| Metronidazoleb | ≤0.03–4 | 0.5 | 0.5 | 403 (100) | 0 (0) |
| Vancomycinc | 0.06–4 | 0.5 | 1 | 401 (99.5) | 2 (0.5) |
| Clindamycinb | 0.06–>256 | 8 | >256 | 55 (13.6) | 296 (73.5) |
| Ciprofloxacin | 0.5–128 | 16 | 64 | ||
| Moxifloxacinb | 0.06–32 | 2 | 16 | 322 (79.9) | 72 (17.9) |
| Levofloxacin | 1–>128 | 4 | 128 | ||
| Gemifloxacin | 0.25–>32 | 2 | 32 | ||
| Nemonoxacin | 0.25–>32 | 1 | 8 | ||
| Tigecycline | ≤0.03–1 | 0.06 | 0.06 | ||
| Daptomycin | 0.06–8 | 1 | 1 | ||
MICs were determined by the agar dilution method with the exception of daptomycin, for which the broth microdilution method was used.
MIC breakpoints applied were those recommended for anaerobes by the Clinical and Laboratory Standards Institute (CLSI-2007, M11-A7) (6). For metronidazole, susceptible, ≤8 μg/ml; resistant, ≥ 32 μg/ml. For clindamycin, susceptible, ≤2 μg/ml; resistant, ≥ 8 μg/ml. For moxifloxacin, susceptible, ≤2 μg/ml; resistant, ≥ 8 μg/ml.
For vancomycin there are no CLSI-recommended MIC breakpoints. Breakpoints are those recommended by The European Committee on Antimicrobial Susceptibility Testing (EUCAST) (susceptible, ≤2 μg/ml; resistant, >2 μg/ml) (13). The two isolates resistant to vancomycin both had vancomycin MICs of 4 μg/ml.