Transwell filter supports

Transfected MDCK cells were seeded on Transwell filter supports (6.5 mm diameter and 0.4 μm pore; Corning). Three days after plating, and after confirming through an inverted microscope that monolayers reached confluency, the TEER was measured using an EVOM epithelial voltmeter (World Precision Instruments) (Betanzos et al., 2013 (link)). TEER values were obtained by subtracting cell-free filter readings.
For some experiments, transfected MDCK cells were apically incubated with live trophozoites (10⁵/cm²) and TEER was monitored during 90 min.

Caco-2Bbe1 cells, a differentiated Caco-2 subclone which attains faster confluency, were purchased from American Type Culture Collection and grown using cell culture conditions as previously described8 (link)24 (link). Cells were harvested with trypsin-EDTA and seeded onto 6.5-mm Transwell filter supports (~1 × 10⁵ cells/insert, Corning, Mississauga, Canada) and maintained for 3–4 d until TER reached >800 Ω cm⁻² measured using chopstick electrodes (Millipore, Etobicoke, Canada)9 (link)39 (link). The apical medium was replaced with prebiotic (10% w/v, 16 h), and then challenged with EHEC (5 h). Data are expressed as percentages of TER at baseline relative to untreated wells.