CLDN5 and infection: The western blot results showed that, compared with the negative control group, the expressions of ZO-1, occludin and claudin-5 in the brains of mice infected by APEC XM and APEC XMΔclbA/pclbA were all significantly decreased, while the expression level in the APEC XMΔclbA infection group was similar to that in the control group (Fig 3A–3D).