Fig. 6: Blr is a streptococcal virulence factor in mice involved in BBB crossing by GBS.

a, b GBS counts in a the brain (including bacteria found in the parenchyma and inside the capillaries) [log10(cfu/g)] and b the blood [log10(cfu/ml)] of mice inoculated with WT GBS at 3 h (n = 10), 6 h (n = 10), 24 h (n = 18), and 48 h (n = 10). One-way ANOVA followed by Sidak’s multiple comparisons tests: p(Brain 24 h vs 48 h) = 0.0003, and Kruskal–Wallis followed by Dunn’s multiple comparisons test: p(Blood 6 h vs 24 h) = 8.5 * 10⁻⁶. c Confocal images showing GBS-GFP (green) attached to and in the capillaries (CD31, red) of the brain parenchyma at 4 h post-injection. d Confocal images of sagittal brain sections of mice injected with a fluorescent GBS WT-GFP strain showing GFP-positive bacteria (green) at the choroid plexus (CP) inside the lateral ventricle (LV; outlined; left image) as well as at the walls of the LV and in the brain parenchyma adjacent to the LV (upper right image), at 24 h post-infection. In the lower right image, a representative cluster of GFP-positive bacteria (also positive for anti-GBS; red) detected in the brain parenchyma. Typical streptococcal chains found in the clusters are presented in the inset. DNA is stained with DAPI (blue). e Kaplan–Meier survival curves of mice intravenously injected with WT GBS (n = 22) or Δblr (n = 10). Log-rank test p = 0.0055. f The ratio of bacterial counts in the brain vs blood [log10([cfu/g brain]/[cfu/ml blood])] in mice inoculated with Δblr was significantly lower than in mice inoculated with WT GBS, at 3 and 6 h post-inoculation (n = 10 for each condition). Two-tailed Student’s t-test, 3 h: p = 0.0351; 6 h: p = 0.0404. For results presented as box and whisker plots: whiskers mark the minimum and maximum, the box includes the 25th–75th percentile, and the line in the box is the median. *p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001; ****p ≤ 0.0001. Source data are provided as a Source Data file for a, b and e, f.