Table 4.
Sequences, resistance levels, and fitness costs of Rif-resistant mutants
| RNAP β subunit (rpoB) mutationa | No. of independent isolates | MIC/MICwtb |
Fitness cost (% per generation [± SEM])c | |
|---|---|---|---|---|
| Rif | Myx | |||
| 464 (509) Ser → Pro | 1 | 2,000 | 1 | 13 (±2) |
| 471 (516) Asp → Gly | 7 | 60 | 1 | 0 (−5 ± 7) |
| 471 (516) Asp → Tyr | 2 | 100 | 1 | 0 (±3) |
| 477 (522) Ala → Asp | 3 | >5,000 | 1 | 9 (±6) |
| 477 (522) Ala → Val | 1 | 100 | 1 | 10 (±5) |
| 481 (526) His → Asn | 1 | 300 | 1 | 0 (−1 ± 2) |
| 481 (526) His → Arg | 1 | >5,000 | 1 | 6 (±4) |
| 481 (526) His → Tyr | 6 | >5,000 | 1 | 14 (±1) |
| 486 (531) Ser → Leu | 2 | >5,000 | 1 | 13 (±6) |
a
Residues are numbered as in S. aureus RNAP and, in parentheses, as in E. coli RNAP.
b
MICs were determined using spiral gradient endpoint assays. The Myx MIC for the wild type (MICwt) is 0.86 μg/ml, and the Rif MICwt is 0.008 μg/ml.
c
Observed fitness costs of the Rif-resistant mutants of ≤0 are shown as 0 and are highlighted in boldface. Observed fitness costs of <0 are shown in parentheses ± standard errors of the means.