Fig. 4.

Bacterial killing by the MPO/H₂O₂/Cl⁻ system. S. aureus (1 × 10⁷ c.f.u. ml⁻¹) in 0·01 M phosphate buffer at pH 7·5 (●), 6·5 (○) or 5·5 (□) was mixed with MPO (5 mg ml⁻¹). H₂O₂ at a concentration of 1 (a), 10 (b) or 100 (c) mM was added. (d) MPO itself had no effect on bacterial viability (□), whilst the bactericidal effect of 100 mM H₂O₂ (●) was prevented in the presence of MPO (5 mg ml⁻¹) (○) at pH 7·5. Each line is representative of the mean (±se) of three experiments.