TABLE 2.
Influence of efflux gene expression on susceptibility of P. aeruginosa to β-lactamase inhibitors
| Strain | Efflux system expresseda | MIC (μg/ml)
|
||
|---|---|---|---|---|
| Cloxacillin | Clavulanate | BRL42715 | ||
| ML5087 | MexAB-OprM | 5,120b | 256 | >1,024 |
| K1110 | 1,024 | 128 | 256 | |
| K1121 | 1,024 | 64 | 512 | |
| K1112 | MexAB-OprM++c | >10,240b | 512–1,024 | >1,024 |
| K1113 | 64 | 64 | 64 | |
| K1114 | MexAB-OprM | >1,024 | 256 | >1,024 |
| K1111 | MexCD-OprJ/MexAB-OprM | >1,024 | 256 | >1,024 |
| K1131 | MexCD-OprJ | 1,024 | 64 | 512 |
| K1115 | 1,024 | 64 | 256 | |
| K1117 | MexEF-OprN | >1,024 | 256 | >1,024 |
| K1116 | 1,024 | 64 | 512 | |
| K1118 | MexEF-OprN | >1,024 | 128–256 | >1,024 |
| K767 | MexAB-OprM | 5,120b | 512 | >1,024 |
| K1119 | 2,560b | 128 | >1,024 | |
| OCR1 | MexAB-OprM++ | >10,240b | 512 | >1,024 |
a
Those efflux systems that are known to be expressed and, thus, that contribute to drug resistance in the indicated strains are indicated.
b
These values were all >1,024 μg/ml in the initial assays. In order to assess differences between the nalB strains OCR1 and K1112 and their parent strains K767 and ML5087, respectively, a second assay was performed with higher concentrations of cloxacillin.
c
The two plus signs denote high-level expression of MexAB-OprM.