Increased susceptibility of the <i>C. diphtheriae</i> C7(β) Δ<i>cat</i> mutant to growth inhibition and killing by H₂O₂.

<p>A: Growth (A600) of wild-type <i>C. diphtheriae</i> C7(β) (left graph) and the isogenic C7(β) Δ<i>cat</i> mutant (right graph) in high-iron PGT medium. At the time points indicated by the downward arrows, H₂O₂ was added at 10 mM (○), 100 mM H₂O₂ (▵), or 300 mM H₂O₂ (□) or was omitted from controls (⧫). B: At the 8 h time points marked by upward arrows in (A) and (B), viability of wild-type <i>C. diphtheriae</i> C7(β) (top row) and C7(β) Δ<i>cat</i> (bottom row) was determined by spotting 30 µl samples from serial dilutions of each culture onto HIA as shown. Spotting cell number illustrate on the left. The photographs show bacterial growth after 14 h at 37°C.