HtrA strongly contributes to virulence after low dose infection with a more modest role for SFP.

<p>Mice were infected with a 10-fold lower inoculum of WT or mutant <i>S. pneumoniae</i> (relative to the infectious dose used in the experiments shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0080062#pone-0080062-g002" target="_blank">figures 2</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0080062#pone-0080062-g004" target="_blank">4</a>; 5×10⁴ CFU) via the intranasal route and euthanized 48 hours later. Bacterial counts were determined in lung (A), blood (B), spleen (C) and liver (D). Data are expressed as box- and whisker plots depicting the smallest observation, lower quartile, median, upper quartile and largest observation. N = 8 mice per group at each time point. * P <0.05, ** P < 0.01, *** P < 0.005 versus WT <i>S. pneumoniae</i>.