TABLE 1.
Cell-based assays to determine MIC values of E. coli DH10B expressing blaPenI and the C69X variants of PenI for selected β-lactams and β-lactam–β-lactamase inhibitor combinations
| Strain | MICa (mg/liter) |
||||||||
|---|---|---|---|---|---|---|---|---|---|
| AMP | THIN | TAX | CAZ | AZT | IMI | AMP-CLAVb | AMP-SULb | PIP-TAZOc | |
| E. coli DH10B pBC SK(+) | 4 | 2 | 0.06 | 0.25 | 1 | 0.5 | 50/0.06 | 50/1 | 2/0.25 |
| E. coli DH10B pBC SK(+) blaPenId | 512 | 256 | 4 | 2 | 8 | 0.25 | 50/0.06 | 50/4 | 4/0.5 |
| C69A | 512 | 512 | 2 | 4 | 1 | 0.25 | 50/0.125 | 50/4 | 4/0.5 |
| C69D | 8 | 4 | 0.125 | 0.5 | 1 | 0.25 | 50/0.06 | 50/1 | 4/0.5 |
| C69E | 8 | 16 | 1 | 4 | 1 | 0.25 | 50/0.06 | 50/1 | 4/0.5 |
| C69F | 8 | 16 | 4 | 64 | 1 | 0.25 | 50/0.06 | 50/1 | 4/0.5 |
| C69G | 256 | 64 | 0.25 | 2 | 1 | 0.25 | 50/0.125 | 50/2 | 8/1 |
| C69H | 64 | 64 | 2 | 16 | 1 | 0.25 | 50/0.06 | 50/1 | 4/0.5 |
| C69I | 256 | 32 | 0.5 | 16 | 1 | 0.25 | 50/0.06 | 50/1 | 8/1 |
| C69K | 8 | 16 | 1 | 16 | 1 | 0.25 | 50/0.06 | 50/1 | 4/0.5 |
| C69L | 512 | 128 | 0.5 | 4 | 1 | 0.5 | 50/0.06 | 50/4 | 8/1 |
| C69 M | 256 | 256 | 2 | 16 | 1 | 0.5 | 50/0.06 | 50/1 | 4/0.5 |
| C69N | 256 | 128 | 0.5 | 8 | 1 | 0.5 | 50/0.06 | 50/2 | 8/1 |
| C69P | 4 | 2 | 0.06 | 0.25 | 1 | 0.25 | 50/0.06 | 50/1 | 2/0.25 |
| C69Q | 64 | 16 | 1 | 16 | 1 | 0.25 | 50/0.06 | 50/1 | 4/0.5 |
| C69R | 8 | 8 | 1 | 16 | 1 | 0.25 | 50/0.06 | 50/1 | 4/0.5 |
| C69S | 256 | 32 | 0.125 | 0.5 | 1 | 0.5 | 50/0.06 | 50/4 | 8/1 |
| C69T | 512 | 256 | 0.5 | 1 | 1 | 0.5 | 50/0.06 | 50/4 | 16/2 |
| C69V | 512 | 64 | 0.5 | 8 | 1 | 0.5 | 50/0.25 | 50/4 | 8/1 |
| C69W | 4 | 8 | 0.125 | 0.5 | 1 | 0.25 | 50/0.06 | 50/1 | 2/0.25 |
| C69Y | 4 | 16 | 8 | 64 | 1 | 0.25 | 50/0.06 | 50/1 | 4/0.5 |
a
β-Lactam and β-lactamase inhibitor abbreviations: AMP, ampicillin; THIN, cephalothin; TAX, cefotaxime; CAZ, ceftazidime; AZT, aztreonam; IMI, imipenem; CLAV, clavulanic acid; SUL, sulbactam; and TAZO, tazobactam. Experiments were completed in triplicate. Elevated CAZ MICs are in boldface.
b
AMP was maintained at a constant concentration of 50 mg/liter, and the clavulanic acid and sulbactam concentrations were varied.
c
Piperacillin and tazobactam were varied at a ratio of 8:1.
d
All of the C69 variants were expressed from pBC SK(+) blaPenI in E. coli DH10B.