TABLE 1.
Frequency of mutants of P. aeruginosa PA14 and its hypermutable mutS derivative resistant to single antibiotics and their combinations with fosfomycin
| Antibiotic(s) | MICa (μg/ml) | Concnb (μg/ml) | Mutant frequency |
|
|---|---|---|---|---|
| WT | mutS | |||
| Fosfomycin | 8 | 128 | 2.3 × 10−6 | 2.1 × 10−4 |
| Tobramycin | 1 | 4 | 2.2 × 10−9 | 1.4 × 10−7 |
| Amikacin | 1 | 16 | 2.6 × 10−9 | 1.2 × 10−7 |
| Imipenem | 0.5 | 8 | 1.5 × 10−7 | 1.6 × 10−5 |
| Meropenem | 0.25 | 8 | 4.2 × 10−8 | 1.3 × 10−6 |
| Ceftazidime | 1 | 8 | 1.3 × 10−8 | 1.3 × 10−6 |
| Ciprofloxacin | 0.1 | 1 | 1.1 × 10−9 | 9.0 × 10−7 |
| Colistin | 0.5 | 2 | <1.0 × 10−10 | <1.0 × 10−10 |
| Tobramycin + fosfomycin | 4 + 128 | <1.0 × 10−10 | <1.0 × 10−10 | |
| Amikacin + fosfomycin | 16 + 128 | <1.0 × 10−10 | <1.0 × 10−10 | |
| Imipenem + fosfomycin | 8 + 128 | 1.1 × 10−9 | 1.1 × 10−7 | |
| Meropenem + fosfomycin | 8 + 128 | <1.0 × 10−10 | <1.0 × 10−10 | |
| Ceftazidime + fosfomycin | 8 + 128 | <1.0 × 10−10 | 1.0 × 10−8 | |
| Ciprofloxacin + fosfomycin | 1 + 128 | <1.0 × 10−10 | <1.0 × 10−10 | |
| Colistin + fosfomycin | 2 + 128 | <1.0 × 10−10 | <1.0 × 10−10 | |
a
The MICs for PA14 (WT) and its mutS derivative were identical in all cases. For all antibiotics, the MIC was determined as recommended by the CLSI (1).
b
Final concentration used for calculation of mutant frequency.