AIEC, strain LF82 disrupts the integrity of polarized epithelial monolayers. Model epithelial cell monolayers [T84 (Panel A) and MDCK-I (Panels B & C)] grown in Transwells were infected with either E. coli, strain LF82 (AIEC) or EHEC O157:H7 – employed as a positive control – for 16 h at 37°C. Both apical (black bar histograms) and basolateral (gray bars) infections of human intestinal T84 monolayers caused a reduction in TER (Panel A; N = 4–6). Similar effects of infection on monolayer integrity were observed when MDCK-I cell monolayers were infected with AIEC, strain LF82 (Panel B), together with an increase in permeability to a macromolecular (10-kilodalton) dextran probe, indicating barrier disruption (Panels C; N = 2–4). HK denotes heat-killed bacteria. ANOVA: * p < 0.05; ** p < 0.01; *** p < 0.001.