Fig. 2.

Second-generation 2-pyridone PS757 has bacteriostatic activity on exponential phase cultures and Atn autolysin-mediated bactericidal activity on nongrowing stationary phase cultures. (A) Growth of exponential phase cultures in the presence of 1/2–4× MIC (3 to 24 µM) of PS757. Exponential phase cultures (OD₆₀₀= 0.2 to 0.3) of OG1RF were split and left untreated (green), treated with DMSO as a vehicle control (orange), and treated with 3 µM (yellow), 6 µM (light green), 12 µM (pink), and 24 µM (purple) PS757 at time 0. The OD₆₀₀ was monitored at 15-, 30-, 60-, and 1,080-min (18 h) time points. To account for change in the OD₆₀₀ due to compound addition, OD₆₀₀ values were normalized by subtracting the change in OD₆₀₀ at t = 0 from t = 15. Black bars represent SD of replicates. (B) Time course killing curves of exponential phase cells. Exponential phase cultures (OD₆₀₀ = 0.2 to 0.3) of OG1RF were split and left untreated (green), treated with DMSO as a vehicle control (orange), and treated with 100 µM (purple) or 50 µM (pink) PS757 at time 0. The CFU/mL were enumerated at time 0, and 2 hr, 4 hr, 6 hr, and 24 hr timepoints posttreatment. (C) Time course killing curves of stationary phase cells. Stationary phase cultures (18 h) of OG1RF were split and left untreated (green), treated with DMSO as a vehicle control (orange), and treated with 100 µM (purple) or 50 µM (pink) PS757 at time 0. The CFU/mL were enumerated at time 0 and 2 hr, 4 hr, 6 hr, and 24 hr time points posttreatment. Black bars represent the SD of the replicates. (D, E) Spot titer assays of PS757-treated mutant cultures. Exponential phase (OD₆₀₀ = 0.2 to 0.3) or stationary phase (18 h) cultures of indicated strains were treated with the vehicle control DMSO (−) or 100 µM PS757 (+) for 24 h. The serial dilution is indicated.