TABLE 3.
Influence of MexAB-OprM on β-lactamase inhibitor enhancement of β-lactam activitya
| β-Lactam | β-Lactamase inhibitor | MIC (μg/ml) for the following strain:
|
||
|---|---|---|---|---|
| K767 (wild type) | K1119 (ΔmexAB-oprM) | OCR1 (nalB) | ||
| Ampicillin | None | 1,024 | 256–512 | NDb |
| Cloxacillin | 256 | 4 | ND | |
| BRL42715 | 64 | <2 | ND | |
| Clavulanate | 1,024 | 512 | ND | |
| Cephaloridine | None | >10,240c | 2,560c | ND |
| Cloxacillin | >1,024 | 258 | ND | |
| BRL42715 | 32 | 4–8 | ND | |
| Clavulanate | >1,024 | >1,024 | ND | |
| Carbenicillin | None | 64 | 1–2 | 256 |
| Cloxacillin | 64 | 1 | 256 | |
| BRL42715 | 64 | 0.125 | 256 | |
| Clavulanate | 64 | 2 | 256 | |
| Piperacillin | None | 4 | 0.25 | 16 |
| Cloxacillin | 4 | 0.25 | 16 | |
| BRL42715 | 8 | 0.125 | 16 | |
| Clavulanate | 4 | 0.25 | 16 | |
a
Determinations of the MICs of the various β-lactams were carried out in the presence of constant amounts (cloxacillin, 100 μg/ml; BRL42715, 20 μg/ml; and clavulanate, 10 μg/ml) of the indicated β-lactamase inhibitors.
b
ND, not determined.
c
These values were >1,024 μg/ml in the initial assays. In order to assess differences between these strains, a second assay was performed with higher concentrations of cephaloridine.