TABLE 2.

Susceptibility phenotypes and associated ampC and ampD RNA expression for P. aeruginosa strains

StrainaMIC (μg/ml) of (susceptibility phenotype for)b:Level of ampC expression (CV)cLevel of ampD1 expression (CV)dLevel of ampDh2 expression (CV)dLevel of ampDh3 expression (CV)dampC statuse
PIPP/TCAZATMFEPBasalInduced
PAO14 (S)f4 (S)1 (S)4 (S)1 (S)1 (0.02)2,705 (0.04)1.00 (<0.01)1.00 (0.01)1.00 (0.01)WT
PA22128 (R)64 (S)16 (I)4 (S)16 (I)84 (0.05)10,854 (0.01)1.40 (<0.01)1.10 (0.03)1.10 (<0.01)PD
PA36764 (S)64 (S)32 (R)4 (S)16 (I)65 (0.01)11,800 (0.02)0.59 (0.02)0.76 (0.02)0.51 (≤0.01)PD
PA24256 (R)128 (R)128 (R)128 (R)64 (R)442 (0.04)7,670 (0.02)1.06 (0.03)0.74 (0.03)0.79 (<0.01)PD
PA113128 (R)64 (S)32 (R)16 (I)16 (I)247 (0.01)5,340 (0.01)0.80 (0.02)0.82 (0.02)0.50 (0.02)PD
GB57>256 (R)f>256 (R)f>128 (R)g>256 (R)f>256 (R)f5,853 (0.03)12,677 (0.03)0.57 (<0.01)0.59 (0.02)0.46 (<0.01)FD
GB61>256 (R)f>256 (R)f128 (R)g48 (R)f32 (R)f1,616 (0.02)6,597 (0.03)0.92 (<0.01)1.04 (0.02)0.31 (0.05)PD
TX291256 (R)>256 (R)f32 (R)64 (R)32 (R)1,919 (0.01)6,994 (0.01)0.93 (0.02)5.20 (0.04)0.75 (0.03)PD
TX292256 (R)>256 (R)f32 (R)64 (R)32 (R)2,990 (0.01)4,715 (0.05)1.13 (<0.01)4.00 (0.03)1.08 (0.03)FD
164CD>1,024 (R)>256 (R)f128 (R)>256 (R)f>256 (R)f6,468 (0.01)5,526 (0.04)1.17 (0.01)1.89 (0.06)0.83 (0.03)FD
  • a Strains PA22, PA367, PA24, and PA113 are cystic fibrosis isolates; strains GB57, GB61, TX291, and TX292 are non-cystic fibrosis clinical isolates; 164CD is a mutant derived from a clinical isolate by selection using ceftazidime.

  • b Susceptibility data were determined and evaluated by agar dilution methodology (unless noted otherwise) as recommended by the CLSI (3). Phenotypic interpretation: S, susceptible; I, intermediate; R, resistant. PIP, piperacillin; P/T, piperacillin-tazobactam; CAZ, ceftazidime; ATM, aztreonam; FEP, cefepime.

  • c The levels of ampC expression in the presence and absence of imipenem were determined by real-time RT-PCR and compared to those in PAO1. The basal level of ampC expression in PAO1 was set at 1. CV, coefficient of variation.

  • d The level of ampD expression relative to that in PAO1 (which was set at 1.00) was determined by real-time RT-PCR. The coefficient of variation for the CT values from at least two independent experiments is shown.

  • e ampC status based on ampC expression data; WT, wild type; PD, partially derepressed; FD, fully derepressed.

  • f The MIC was determined by Etest (AB Biodisk, Sweden).

  • g The MIC was determined by broth microdilution.