Adhesion assay
The BMECs were washed with PBS three times, and one milliliter triton-X-100 (0.5% V/V, Solarbio Life Science, Beijing, China) was added in each well after incubation with LCZ or E. coli . The cells were scraped off, and the lysate was transferred to a 1.5-mL centrifuge tube after 10 min of stabilization at room temperature.E. coli and LCZ were plated on TSA and MRS agar, respectively, after serial dilution and were quantified by determination of CFU.
Measurement of the trans-epithelial electric resistance
To measure the trans-epithelial electric resistance (TEER) of monolayer BMECs, BMECs were seeded to confluence on transwell inserts (membrane area 0.33 cm2, pore size 0.4 μm, Corning, NY, USA) and a polarized and differentiated state was achieved within 5 days after seeding. TEER was measured immediately after different treatments with a Millicell Electrical Resistance System-2 (Millipore, MA, USA). Measurements of TEER were made three times per well and expressed as Ω∙cm2 after subtracting the filter resistance value. The results of TEER were expressed as change of TEER (TEER of monolayer cells after treatments - TEER of monolayer cells before treatments).