Fig. 5. An in vivo model of brain infection in Drosophila identifies Blr as a virulence factor and confirms LpR2 as a BBB receptor for brain invasion by GBS.

a Schematic representation of Drosophila third instar larva injected with GBS. Confocal picture and close-up (top and orthogonal views) showing GBS (in green) inside the brain, 4 h after microinjection. b GBS brain entry 4 h post-injection for WT GBS (n = 18), Δlgt/lsp (n = 19), Δblr (n = 23) and Δblr + blr (n = 20). A Kruskal–Wallis test followed by Dunn’s multiple comparisons test generated adjusted p-values: Δlgt/lsp p = 0.0168, Δblr p = 0.0039, Δblr + blr p = 0.6579. c Kaplan–Meier survival curves for larvae injected with mock, WT GBS, Δlgt/lsp, Δblr and Δblr + blr strains (n = 60 for each condition) show that Δlgt/lsp and Δblr are avirulent. Log-rank test: p(WT GBS vs mock) <0.0001; p(WT GBS vs Δlgt/lsp) = 0.001; p(WT GBS vs Δblr) <0.0001; p(WT GBS vs Δblr + blr) = 0.7308, and p(mock vs Δblr) = 0.9686. d GBS brain entry at 4 h post-injection in control (n = 13) and LpR2 knockdown (n = 24) larvae. Two-tailed Mann–Whitney test: p = 4 * 10⁻⁸. e Kaplan–Meier survival curves for control larvae and larvae in which LpR2 has been knocked down in the SPG (SPG > LpR2 RNAi), injected with mock or WT GBS (n = 60 for each condition). Log-rank test: p(Control + WT GBS vs SPG > LpR2 RNAi + WT GBS) = 0.16; p(SPG > LpR2 RNAi vs SPG > LpR2 RNAi + WT GBS) = 0.13. For c and e, log-rank p-values were adjusted through stacked p-values analysis by the Holm–Sidak method. Kaplan–Meier curves show error bars corresponding to standard errors (SE). 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. n represents the number of larvae analysed. *p ≤ 0.05; **p ≤ 0.01; ****p ≤ 0.0001; ns, not significant. Source data are provided as a Source Data file for b–e.