FIG 4.

ESR determination of hydroxyl radicals formed in S. aureus. Hydroxyl-radical signals were detected in S. aureus cells resuspended in 50 mM sodium sulfate buffer using the DMPO probe. Cells were treated with 6 mM hydrogen peroxide, 2.5 μg/ml vancomycin, or 0.4 μg/ml ciprofloxacin. Measurements at 15 min (black columns) and 35 min (gray columns) of treatment are shown.