TABLE 1.
Susceptibility of vancomycin-susceptible and vancomycin-resistant enterococci to penicillin, ampicillin, and imipenema
| Microorganism (n) | Antimicrobial agent | MIC range (μg/ml) | MIC50 (μg/ml) | MIC90 (μg/ml) |
|---|---|---|---|---|
| Vancomycin-susceptible E. faecalis (175) | Penicillin | 0.5–16 | 4 | 4 |
| Ampicillin | 0.25–4 | 1 | 2 | |
| Imipenem | 0.06–4 | 1 | 2 | |
| Vancomycin-resistant E. faecalis (24) | Penicillin | 2–4 | 4 | 4 |
| Ampicillin | 0.5–4 | 1 | 2 | |
| Imipenem | 0.5–2 | 1 | 2 | |
| Vancomycin-susceptible E. faecium (5) | Penicillin | 2–>64 | ||
| Ampicillin | 1–>64 | |||
| Imipenem | 0.5–>64 | |||
| Vancomycin-resistant E. faecium (19) | Penicillin | >64 | >64 | >64 |
| Ampicillin | ≥64 | >64 | >64 | |
| Imipenem | ≥64 | >64 | >64 |
a
Two E. faecalis strains were intermediately susceptible to vancomycin (MIC = 8 μg/ml). Empty cells indicate that the MIC50 and MIC90 were not calculated (n < 10).