Table 2. Quinolone resistance-determining region (QRDR) mutations and minimal inhibitory concentration of quinolones for surviving mutants obtained in the mutant prevention concentration (MPC) assay.
| Strain* | Mutant | MPC(μg/ml) | QRDR mutations | MIC (μg/ml)† | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| GyrA | GyrB | ParC | ParE | NAL | CIP | OFX | LVX | |||||||
| E. coli ATCC25922/pDIJ09-518a | #1 | 1 | S83L | - | - | - | >256 | R | 0.125 | S | 0.38 | I | 0.19 | S |
| #2 | 1 | S83W | - | - | - | 24 | R | 0.25 | S | 0.5 | I | 0.38 | S | |
| #3 | 1 | S83W | - | - | - | >256 | R | 0.38 | I | 0.75 | R | 0.38 | S | |
| #4 | 1 | S83W | - | - | - | 24 | R | 0.19 | S | 0.5 | I | 0.25 | S | |
| #5 | 1 | S83W | - | - | - | >256 | R | 0.125 | S | 0.38 | I | 0.19 | S | |
| E. coli ATCC25922/pDIJ09-518a + TOB | #1 | 2 | S83W | - | - | - | >256 | R | 1 | R | 4 | R | 1 | I |
| #2 | 2 | S83W | - | G78D | - | >256 | R | 0.38 | I | 2 | R | 0.75 | I | |
| #3 | 2 | S83W | - | G78D | - | >256 | R | 1.5 | R | 4 | R | 0.75 | I | |
| #4 | 2 | S83W | - | G78D | - | >256 | R | 1 | R | 6 | R | 1 | I | |
| #5 | 2 | S83W | - | - | - | >256 | R | 1 | R | 4 | R | 1 | I | |
*
+TOB stands for strains exposed to sub-MIC of tobramycin prior to MPC assay.
†
Susceptibility testing categories according to EUCAST clinical breakpoints. Nalidixic acid: R > 16 μg/ml. Levofloxacin: S ≤ 0.5 μg/ml, R > 1 μg/ml. Ofloxacin: S ≤ 0.25 μg/ml, R > 0.5 μg/ml. Ciprofloxacin: S ≤ 0.25 μg/ml, R > 0.5 μg/ml.