Table 1.

Selection of first- and second-step mutants

StrainaMIC (μg/ml)Frequency of mutation at:Changes in:
TrovafloxacinCiprofloxacinLevofloxacinSparfloxacinPefloxacin2× the MIC4× the MIC8× the MICGrlAGrlBGyrAGyrB
Parent strain RN42200.0150.250.1250.0630.25NoneNoneNoneNone
First-step mutants
 4220-53T0.12520.50.06341.1 × 10−101.1 × 10−10<1.1 × 10−10Ser80 to PheNoneNoneNone
 4220-54T0.12520.50.0634Ser80 to TyrNoneNoneNone
 4220-55T0.06320.50.0634Ser80 to TyrNoneNoneNone
 4220-56T0.12520.50.0634Ser80 to PheNoneNoneNone
 4220-16C0.06310.50.1254Glu84 to LysNoneNoneNone
 4220-19C0.125210.1254Ser80 to PheNoneNoneNone
 4220-20C0.12510.50.1254Ser80 to PheNoneNoneNone
 4220-57C0.06320.50.06343.1 × 10−73.0 × 10−8<4.6 × 10−9Glu84 to LysNoneNoneNone
 4220-58C0.12520.50.0634Ser80 to PheNoneNoneNone
 4220-5L0.06320.50.12543.0 × 10−73.2 × 10−8<1.4 × 10−9NonePro451 to GlnNoneNone
 4220-7L0.12520.50.1254Gly78 to CysNoneNoneNone
 4220-9L0.12520.50.1254Ser80 to PheNoneNoneNone
 4220-11L0.12520.50.1254Ser80 to PheNoneNoneNone
 4220-1P0.12520.50.12541.03 × 10−7<4.4 × 10−9<4.4 × 10−9Ser80 to PheNoneNoneNone
 4220-3P0.12520.50.1254Glu84 to LysNoneNoneNone
 4220-5P0.12520.50.1254Ser80 to PheNoneNoneNone
 4220-7P0.12520.50.1254Ser80 to TyrNoneNoneNone
Second-step mutants
 4220-16-3S0.25888323.5 × 10−83.3 × 10−82.1 × 10−8Glu84 to LysNoneSer84 to LeuNone
 4220-16-8S0.584832Glu84 to LysNoneSer84 to LeuNone
 4220-16-10S0.2588432Glu84 to LysNoneGlu88 to LysNone
 4220-16-21S0.2584432Glu84 to LysNoneGlu88 to LysNone
 4220-19-1S1848321.6 × 10−81.3 × 10−81.8 × 10−8Ser80 to PheNoneSer84 to LeuNone
 4220-19-6S184432Ser80 to PheNoneGlu88 to LysNone
 4220-19-12S184832Ser80 to PheNoneSer84 to LeuNone
 4220-19-23S184432Ser80 to PheNoneGlu88 to LysNone
 4220-20-48C184432Ser80 to PheNoneSer84 to LeuNone
  • a The strain number followed by T, C, L, P, or S designates mutant selected with trovafloxacin, ciprofloxacin, levofloxacin, pefloxacin, or sparfloxacin, respectively. The first-step mutants were selected with trovafloxacin or perfloxacin at 2× the MIC for RN4220 or with ciprofloxacin or levofloxacin at 4× the MIC for RN4220.