TABLE 1.
Resistance mutations in the atpE gene and MIC levelsa
| Parent strain group and strain | Selection concn (multiple of MIC) | No. of mutants sequenced (total no. obtained) | atpE, F0 operon, or ATP synthase operon mutation | No. of independent mutants | MIC range (mg/liter) |
|---|---|---|---|---|---|
| MDR parent strains | |||||
| 1 | 10 | 6 (12) | Glu61 → Asp (GAG-GAC) | 1 | 0.48 |
| WT atpE | 5 | 0.12-0.48 | |||
| 30 | 2 (2) | Ala63 → Pro (GCA-CCA) | 2 | 1.92-3.84 | |
| 2 | 10 | 3 (5) | Asp28 → Val (GAC-GTC) | 1 | 0.48 |
| Glu61 → Asp (GAG-GAC) | 1 | 0.24 | |||
| WT atpE | 1 | 0.12 | |||
| 30 | 0 (0) | ||||
| 3 | 10 | 6 (12) | WT atpE | 2 | 0.9 |
| WT atpE and F0 operon | 1 | 0.9 | |||
| WT atpE and ATP synthase | 3 | 0.9 | |||
| 30 | 5 (11) | WT atpE | 3 | 0.48-0.9 | |
| WT atpE and F0 operon | 2 | 0.9 | |||
| 5 | 10 | 3 (7) | WT atpE | 2 | 0.12-0.24 |
| WT atpE and F0 operon | 1 | 0.24 | |||
| 30 | 2 (2) | Ala63 → Pro (GCA-CCA) | 1 | 0.9 | |
| Ile66 → Met (ATC-ATG) | 1 | 0.48 | |||
| Drug-susceptible parent strains | |||||
| 4 | 10 | 7 (12) | Asp28 → Pro (GAC-GGC) | 1 | 0.3 |
| Glu61 → Asp (GAG-GAC) | 1 | 0.96 | |||
| WT atpE | 3 | 0.12-0.24 | |||
| WT atpE and F0 operon | 2 | 0.3-0.48 | |||
| 30 | 1 (1) | Glu61 → Asp (GAG-GAC) | 1 | 0.48 | |
| 6 | 10 | 5 (10) | WT atpE | 5 | 0.24-0.96 |
| 30 | 5 (5) | Glu61 → Asp (GAG-GAC) | 1 | 0.48 | |
| Ala63 → Pro (GCA-CCA) | 1 | 0.9 | |||
| WT atpE | 3 | 0.12-24 | |||
| 7 | 10 | 3 (10) | WT atpE | 1 | 0.48 |
| WT atpE and F0 operon | 2 | 0.48 | |||
| 30 | 5 (5) | Ala63 → Pro (GCA-CCA) | 3 | 3.84 | |
| WT atpE | 2 | 0.24-0.48 |
a
The atpE genes of 53 mutants (33 selected at 10× MIC [0.3 mg/liter] and 20 selected at 30× MIC [0.9 mg/liter]) were sequenced, and six different classes of mutations were identified. The first five classes represented single point mutations within the atpE gene; and the last group, which consisted of 38 mutant clones, represented mutants in which no mutation within the sequenced gene was identified. Eleven of the mutants exhibited wild-type (WT) F0 operons, and three of these had wild-type ATP synthase (F0 and F1 operons).