Fig 1

A,B. S. sonnei is more virulent than S. flexneri in vivo. Survival curves (A) and Log₁₀-transformed CFU counts (B) of larvae injected in the hindbrain ventricle (HBV) with PBS (grey), S. flexneri (blue) or S. sonnei (red). Experiments are cumulative of 3 biological replicates. In B, full symbols represent live larvae and empty symbols represent larvae that at the plating timepoint had died within the last 16 hours. Statistics: Log-rank (Mantel-Cox) test (A); unpaired t-test on Log₁₀-transformed values (B); **p<0.0021; ***p<0.0002; ****p< 0.0001. C,D. S. sonnei elicits a stronger inflammatory signature than S. flexneri in vivo. Quantitative real time PCR for representative inflammatory markers were performed on pools of 20 HBV injected larvae collected at 6 (C) or 24 (D) hpi with PBS (grey), S. flexneri (blue) or S. sonnei (red). Experiments are cumulative of 4 biological replicates. Statistics: one-way ANOVA with Sidak’s correction on Log₂-transformed values; ns, non-significant; *p<0.0332 **p<0.0021; ***p<0.0002; ****p<0.0001. E,F. S. sonnei can disseminate from the injection site. Representative images of three GFP-labelled S. flexneri-infected (E) or S. sonnei-infected (F) larvae at 24 hpi. In D, arrows indicate dissemination in the blood circulation; arrowheads indicate dissemination in the neuronal tube. Scale bars = 1 mm.