TABLE 1

Representative Rifr E. coli K12 (MG1655) relative fitness

Mutant% growth/generation
(vs. K12 parent)a
(±SEM)
MIC
(μg/ml rif)b
rpoB substitutioncMutation
clusterd
K12100 (±0.1)0-12.5
rif-186.4 (±1.4)100-200I572L (ATC to CTC)II
rif-286.5 (±1.8)25-50L511Q (CTG to CAG)II
rif-394.4 (±1.5)100-200H526L (CAC to CTC)II
rif-4104.6 (±1.4)100-200None identified in I or in II
rif-596.3 (±0.9)200-400Q148L (CAG to CTG)I
rif-691.3 (±1.0)200-400H526Y (CAC to TAC)II
rif-789.6 (±2.1)50-100Q148L (CAG to CTG)I
rif-883.5 (±1.9)3000-4000P564L (CCT to CTT)II
rif-9103.0 (±0.2)100-200D516G (GAC to GGC)II
  • a Relative fitness (mutation cost) was determined via direct competition between Rifr mutants (rif-1-9, here mal+) and a Rifs K12 MG1655 carrying a neutral marker [mal]. The standard error for the cost estimate (derived from 10 independent completion assays) is shown in parentheses. A value below 100% indicates that the strain tested was at a reproductive disadvantage relative to the wild-type reference strain. A fitness value in excess of 100% indicates that the strain tested exhibited a reproductive advantage relative to the wild type.

  • b The concentration interval indicated for MIC denotes the range within which the true MIC for rifampin exists.

  • c Substitutions are abbreviated as follows: original amino acid (single letter code) followed by amino acid number, followed by substituted amino acid (e.g., I572L signifies an isoleucine has been replaced by a leucine at position 572). The altered codon is shown in parentheses.

  • d See Figure 2 for locations of resistance clusters I and II.