Compared with the negative control group, the expression of ZO-1 (Fig 4B–4D), claudin-5 (Fig 5B–5D) and occludin (Fig 6B–6D) in the pia mater, cerebral cortex and hippocampus of mice brains infected by APEC XM and APEC XMΔclbA/pclbA was significantly decreased, while the expression level in the APEC XMΔclbA infection group was similar to that in the control group. Here, CLDN5 is linked to infection.