FIG. 4.

HtrA is required for full virulence of L. monocytogenes 10403S in mice. Eight-week-old female BALB/c mice (groups of five) were injected intravenously with 2 × 10⁴ CFU of wild-type or htrA mutant L. monocytogenes. Three days postchallenge, the numbers of CFU in their livers (A) and spleens (B) were determined. Data represent the mean (± the standard error of the mean [error bars]) number of CFU per organ from organs of 10 mice pooled from two separate experiments. The Mann-Whitney rank sum test was used for statistical analysis. The numbers of CFU per liver (P < 0.009) and per spleen (P < 0.002) in htrA mutant-infected mice were significantly reduced compared to those in wild-type L. monocytogenes 10403S-infected mice.