Fig. 2.

Pneumococcal H₂O₂ is responsible for bronchial epithelial cell lysis. a Monitoring of growth behavior of S. pneumoniae D39∆cps, ∆cps∆ply, ∆cps∆spxB, and ∆cps∆ply ∆spxB mutant strains in THY medium (n = 3). b H₂O₂ production by pneumococci was determined by colorimetric analysis of bacterial culture supernatants (n = 4). 16HBE cells were infected with pneumococcal strains, and bacterial infectivity (c, e) and cytotoxicity toward the cells (d, f) were assessed at indicated time points (n ≥ 4). The data in (b, c, e) are displayed as box plots. Bars in (d, f) denote mean values ± SD. The level of significance was determined using Kruskal-Wallis test with Dunn's post-test (n ≥ 4; n.s., not significant; *p < 0.05; **p < 0.01; ***p < 0.001). CFU, colony-forming unit; SD, standard deviation; THY, Todd-Hewitt broth supplemented with 0.5% (w/v) yeast extract.