Table 3

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

RNAP subunit and amino acid substitutionaNo. of independent isolatesMIC/MICwtbFitness cost (% per generation [± SEM])
MyxRif
β Subunit (rpoB)
    1080 (1275) Val → Ile12018 (±2)
    1080 (1275) Val → Leu120112 (±3)
    1084 (1279) Glu → Lys1>10018 (±4)
    1101 (1296) Asp → Glu120115 (±1)
    1127 (1322) Ser → Leu3>100110 (±3)
    1127 (1322) Ser → Pro2>10014 (±2)
β′ Subunit (rpoC)
    334 (345) Lys → Asn3>10016 (±2)
    925 (917) Thr → Lys12017 (±1)
    925 (917) Thr → Arg1>10015 (±2)
    1172 (1354) Gly → Cys120113 (±1)
    1172 (1354) Gly → Asp220114 (±1)
  • 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 MIC of the wild-type parent (MICwt) is 0.86 μg/ml for Myx and 0.008 μg/ml for Rif.