Fig. 6: Administration of leucine attenuates NMEC virulence.

a, b qRT-PCR analysis of the NsrP (a) and purD (b) expression in mouse blood were determined 4 h after intravenous injection of 1 × 10⁶ CFU of the NMEC with the administration of leucine or PBS. (c, d, f–k) Bacterial counts in the blood (CFU/mL, c, f–j) and meningitis development (d, k) were determined 4 h after intravenous injection of 1 × 10⁶ CFU of the WT (c), ΔpurD (f), ΔNsrP (g), NsrP^pro-mut (h), NsrP^bind-mut (i), and PurD^syn-mut (j) strains with the administration of leucine or PBS at 0.5 h post-infection (n = 8 for each group). CSF culture positivity was defined as meningitis (d, k). e H&E staining of the brain sections was performed 4 h after intravenous injection of 1 × 10⁶ CFU of the WT strain and of leucine or PBS at 0.5 h post-infection. The right panels are higher-magnification images of the boxed regions, showing meningeal thickening and neutrophil infiltration (arrows). Scale bar, 100 μm. The images shown are representative of three independent experiments. l The distribution of NsrP in 930 publicly available complete E. coli genomes. In a, b, data were presented as the means ± SDs (n = 3 independent experiments). ns nonsignificant. Two-tailed unpaired Student’s t-test (a, b) and two-tailed Mann–Whitney U-test (c, f–j) were applied.