TABLE 3.
Effect of mexAB-oprM operon on LVX susceptibility of strains with multiple target mutations
| gyrA or parC mutation | MIC (μg/ml) for indicated strain with the following pump status:
|
||
|---|---|---|---|
| nalBa | WTb | oprM::ΩHgc | |
| None | 2 (PAM1032) | 0.25 (PAM1020) | 0.015 (PAM1154) |
| gyrA (Thr83→Ile) | 8 (PAM1573) | 2 (PAM1548) | 0.125 (PAM1665) |
| gyrA (Thr83→Ile) parC (Ser87→Leu) | 32 (PAM1582) | 4 (PAM1667) | 0.5 (PAM1600) |
| gyrA (Thr83→Ile) parC (Ser87→Leu) gyrA (Asp87→Tyr) | 128 (PAM1609) | 16 (PAM1669) | 2 (PAM1640) |
The strains were obtained by stepwise selection with increasing concentrations of LVX. Strain PAM1032 was selected from wild-type strain PAM1020. The order of the strains in the column corresponds to the order in which the strains were selected, so that for example, PAM1032 is a parent of PAM1573. All mutant selections were performed with LVX at 4× the MIC for the corresponding parent.
WT, wild type. PAM1548 was obtained as a spontaneous LVX-resistant mutant selected from strain PAM1020. PAM1667 and PAM1669 were constructed by transduction of the mexAB-oprM operon with the wild-type level of expression (no nalB mutation) from strain PAM1064 into PAM1582 and PAM1609, respectively, as described in Materials and Methods.
Strains PAM1665, PAM1600, and PAM1640 were constructed by transduction of the Hg resistance from strain PAM1154 (PAM1020 oprM::ΩHg) into strains PAM1573, PAM1582, and PAM1609, respectively.