Table 1.
Beta-lactam susceptibilities of penicillin-resistant, ampicillin-susceptible Enterococcus faecalis (n = 59) and penicillin-susceptible, ampicillin-susceptible E. faecalis (n = 15) isolates according to different methods and the interpretative discrepancies considering the broth dilution as gold standard
| Antimicrobial | Method | Number of isolates | Number (%) of | EA (%) | CA (%) | ||
|---|---|---|---|---|---|---|---|
| Resistant | Susceptible | VME | ME | ||||
| Penicillin | Broth dilution | 59 | 15 | ||||
| Etest | 54 | 20 | 5 (8.5) | 0 | 91.9 | 93.4 | |
| Disk diffusion | 57 | 17 | 2 (3.4) | 0 | NAe | 97.3 | |
| Ampicillin | Broth dilution | 0 | 74 | ||||
| Etest | 0 | 74 | NA | 0 | 91.9 | 100 | |
| Disk diffusion | 13 | 61 | NA | 13 (17.6) | NAe | 82.4 | |
| Amoxicillin | Broth dilution | 0 | 74 | ||||
| Etest | 0 | 74 | NA | 0 | 91.9 | 100 | |
| Disk diffusion | 4 | 70 | NA | 4 (5.4) | NA | 94.6 | |
| Imipenem | Broth dilution | 16 | 58 | ||||
| Etest | 27 | 47 | 0 | 11 (19.0) | 94.6 | 85.1 | |
| Disk diffusion | 37 | 37 | 6 (37.5) | 27 (46.5) | NAe | 55.4 | |
| Piperacillin | Broth dilution | 58 | 16 | ||||
| Etest | 57 | 17 | 1 (1.7) | 0 | 75.7 | 98.6 | |
| Disk diffusion | 45 | 29 | 14 (24.1) | 1 (6.3) | NAe | 79.7 | |
VME very major errors (false susceptibility), ME major errors (false resistance), EA essential agreement, CA categorical agreement, NA not applicable