TABLE 2.
ISAba1 transposition frequency in E. coli without and with antibioticsa
| Antibiotic (μg/ml) | Transposition frequency [(mean ± SD) × 10−7] |
|---|---|
| None | 2.1 ± 1.0 |
| Ceftazidime (0.12) | 1.8 ± 0.8 |
| Ceftazidime (0.06) | 2.4 ± 0.5 |
| Ceftazidime (0.02) | 7.5 ± 5.8 |
| Cefotaxime (0.02) | 5.2 ± 1.7 |
| Cefotaxime (0.01) | 3.2 ± 2.1 |
| Cefotaxime (0.005) | 4.0 ± 3.2 |
| Ciprofloxacin (0.001) | 3.3 ± 2.6 |
| Ciprofloxacin (0.0005) | 3.6 ± 0.6 |
| Ciprofloxacin (0.0002) | 2.6 ± 1.0 |
| Imipenem (0.06) | 1.4 ± 1.1 |
| Imipenem (0.03) | 6.6 ± 6.1 |
| Imipenem (0.01) | 3.4 ± 2.0 |
| Nalidixic acid (0.5) | 4.5 ± 3.1 |
| Nalidixic acid (0.25) | 1.2 ± 0.7 |
| Nalidixic acid (0.1) | 1.6 ± 1.0 |
| Piperacillin (6) | 2.9 ± 0.2 |
| Piperacillin (3) | 1.8 ± 0.2 |
| Piperacillin (1) | 3.1 ± 3.8 |
a
In each case, three independent experiments were performed, and the mean and standard deviations were calculated. Statistical analysis was performed using the Student t test, and a P value of ≤0.05 was considered significant. MICs for the E. coli RZ211 strain (pISAba1-TEM-1) were as follows: ceftazidime, 0.25 μg/ml; cefotaxime, 0.047 μg/ml; ciprofloxacin, 0.002 μg/ml; imipenem, 0.12 μg/ml; nalidixic acid, 1 μg/ml; and piperacillin, 12 μg/ml.