TABLE 1.

MICs for and inhibition zone diameters of strains PAO1 and PAOΔmutS and their respective resistant mutant subpopulations

AntibioticPAO1aPAOΔmutSaNCCLS breakpointsc
Etest MIC (μg/ml)Disk diffusion diam (mm)EtestDisk diffusionN, R MIC (μg/ml)R, N diam (mm)
MIC (μg/ml)MIC for the subpopulation (relative no.)bDiam (mm)Diam of the subpopulation (relative no.)
Ceftazidime125.6148 (+++)25.414.1 (+++)≤8, ≥32≤14, ≥18
Imipenem1.521.91.512 (+ to ++)22.814.8 (++)≤4, ≥16≤13, ≥16
Meropenem0.3829.40.53 (++)27.219.0 (++)≤4, ≥16≤13, ≥16
Ciprofloxacin0.06432.40.0640.38 (++)34.029.6 (++)≤1, ≥4≤15, ≥12
Tobramycin1.520.023 (+)18.015.0 (+)≤4, ≥16≤12, ≥15
  • a Results shown are the median values of five independent determinations. MICs and inhibition zone diameters were measured at 24 h for the general population and at 36 h for the resistant mutant subpopulation. The highest MICs or the smallest inhibition zone diameters of resistant mutant subpopulations are listed.

  • b Relative number of resistant mutant colonies (see Materials and Methods). +, < 10 mutants; ++ 10 to 100 mutants; +++, > 100 mutants.

  • c N, nonsuceptibility breakpoint; R, resistance breakpoint.