FIG 6.

Pathogenesis of the 4496 strain versus the 4496ΔPPI1 mutant in mice. Two groups of 8 mice were infected intranasally with 10⁷ CFU of the 4496 or 4496ΔPPI1 strain. At 24 h and 36 h postchallenge, numbers of pneumococci in the nasopharynx (A), lung (B), pleural cavity (C), and blood (D) were determined. Horizontal broken lines indicate the geometric mean bacterial load for each group. The horizontal dotted line indicates the limit of detection (LD). At the 12-h time point, this equates to 10² CFU in all niches; at 24 h and 36 h, this equates to 10² CFU in nasopharynx and lung and to 2 × 10² CFU in the pleural lavage fluid and blood. Statistical differences were analyzed by two-tailed unpaired t tests performed on log-transformed data (*, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001).