Table 2. MICs (mg/L) of β-lactams for several carbapenemase producers and reference strain Escherichia coli DH10B.
| β-Lactam(s)* | Enterobacter asburiae MS7† | E. cloacae 1413B† | Escherichia coli DH10B (pNat)‡ | E. coli DH10B (pIMI-2)‡ | E. coli DH10B |
|---|---|---|---|---|---|
| Amoxicillin | >512 | >512 | >512 | >512 | 4 |
| Amoxicillin + CLA | >512 | >512 | >512 | >512 | 4 |
| Ticarcillin | 128 | >256 | 128 | 256 | 4 |
| Ticarcillin + CLA | 16 | >256 | 16 | 32 | 4 |
| Piperacillin | 16 | >256 | 8 | 128 | 2 |
| Piperacillin + TZB | 4 | >256 | 2 | 16 | 2 |
| Cephalothin | 512 | >256 | 64 | 512 | 4 |
| Cefotaxime | 0.06 | 1 | 0.06 | 1 | 0.06 |
| Ceftazidime | 0.12 | 2 | 0.06 | 0.5 | 0.25 |
| Aztreonam | 4 | 8 | 4 | 64 | 0.12 |
| Imipenem | >64 | >64 | 16 | >64 | 0.06 |
| Meropenem | 32 | 4 | 2 | 32 | 0.06 |
*CLA, clavulanic acid at a fixed concentration of 2 mg/L; TZB, tazobactam at a fixed concentration of 4 mg/L. †Enterobacter asburiae MS7 produces acquired β-lactamase IMI-2, whereas E. cloacae 1413B produces acquired β-lactamases TEM-1 and IMI-1 (5). ‡Natural plasmid pNat harbors the blaIMI-2 gene, whereas pIMI-2 is a recombinant plasmid that has the same β-lactamase gene.