Table 2.
Frequency of spontaneous mutations conferring resistance to rifampicin and nalidixic acid
| Genotype | Mutation frequency per 109 cells |
||
|---|---|---|---|
| Mean ± SEM | Fold difference | n | |
| RifampicinR | |||
| Wild type | 19.3 ± 3.7 | 1.0 | 39 |
| mutLdown + tc | 22.4 ± 4.3 | 1.1 | 39 |
| mutLdown − tc | 2,468 ± 286 | 127.8* | 20 |
| mutL | 6,504 ± 394 | 336.6* | 32 |
| Wild-type pVector | 37.2 ± 14.2 | 1.0 | 19 |
| Wild-type pMutL | 51.8 ± 20.4 | 1.3 | 20 |
| Wild-type pMutS | 23.8 ± 3.5 | 0.6 | 10 |
| Nalidixic acidR | |||
| Wild type | 2.7 ± 0.6 | 1.0 | 17 |
| mutLdown + tc | 2.4 ± 0.6 | 0.9 | 16 |
| mutLdown − tc | 990 ± 116 | 361.3* | 20 |
| mutL | 1,450 ± 144 | 531.2* | 35 |
Fold difference is the ratio of the value for a given strain to the value of the control strain, i.e., the first strain in every subdivision of the column. tc, tetracycline.
*Difference is significant according to Mann–Whitney test, P < 0.05.