Epithelial tight junctions are disrupted by AIEC infection. MDCK-I monolayers were grown to confluence on 6.5 mm diameter Transwells and then either left uninfected (sham control; Panel A) or infected with AIEC, strain LF82 (Panel B) at a MOI of 100:1 for 16 h. Monolayers were then washed with PBS and fixed, blocked and incubated with primary rabbit anti-ZO-1 and the appropriate secondary antibody and DAPI. Panel A: Sham control cells showed a normal distribution of ZO-1, outlining the intercellular tight junctions. Panel B: AIEC infection resulted in disruption of ZO-1 localization with large gaps between cells (arrows). Approximate original magnifications: × 630.