(A) Equivalent titers of aerobic stationary phase bacteria grown in TSB broth were added to molten top-agarose and poured onto TSB agar plates. Filter paper disks (7 mm) impregnated with 8.8 M H2O2 were then placed on the solidified top agarose. Small white bars, the precise width of the killing zone, are placed just above each zone for ease of viewing. (B) Approximately 106 stationary phase bacteria were sub-cultured into fresh TSB containing increasing concentration of H2O2 after which the MICs were determined 24 hr post-exposure. Lane 1, wild-type; lane 2, oxyR; lane 3, oxyR-poxyR; lane 4, oxyR + pahpB; lane 5, oxyR + pkatB; lane 6, oxyR + pahpCF.