Table 4

Sequences, resistance levels, and fitness costs of Rif-resistant mutants

RNAP β subunit (rpoB) mutationaNo. of independent isolatesMIC/MICwtbFitness cost (% per generation [± SEM])c
RifMyx
464 (509) Ser → Pro12,000113 (±2)
471 (516) Asp → Gly76010 (5 ± 7)
471 (516) Asp → Tyr210010 (±3)
477 (522) Ala → Asp3>5,00019 (±6)
477 (522) Ala → Val1100110 (±5)
481 (526) His → Asn130010 (1 ± 2)
481 (526) His → Arg1>5,00016 (±4)
481 (526) His → Tyr6>5,000114 (±1)
486 (531) Ser → Leu2>5,000113 (±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.