FIG. 1.

Effect of hydrogen peroxide production and SpxB expression on hydrogen peroxide resistance. (A) After growth to mid-log phase, cultures of type 2 phase variants P125 (░⃞) and P126 (□) or type 4 phase variants P836 (░⃞) and P835 (□) were incubated in TS containing 20 mM H₂O₂ for 30 min. (B) After growth to mid-log phase, cultures of wild type (░⃞), spxB mutant (□), or spxB mutant complemented with pMU1328::300+spxB (▨) were incubated in TH+Y (D39) or TS (R6x) containing 20 mM H₂O₂ for 30 min. Values are the average of three independent determinations in duplicate and represent the change in CFU expressed as a percentage of the control culture without hydrogen peroxide ± the standard deviation (SD). Symbols: †, below the limit of detection; ✽, P < 0.05. (C) Relative expression of SpxB in different S. pneumoniae strains. Cell lysates of D39 (lane 1), P878 (lane 2), P1221 (lane 3), R6x (lane 4), P1167 (lane 5), and P1185 (lane 6) were electrophoresed on a 10% SDS-polyacrylamide gel, transferred to a polyvinylidene difluoride membrane, and immunoblotted with an antibody to SpxB. Size markers are given in kilodaltons.