mL-1 in cell culture medium without serum and antibiotics. Caco-2/TC7 cells grown on 24-wells culture plates or inserts were washed twice with fresh Baf-A1 culture medium and the bacterial suspensions were applied to the cell surface at a concentration of 108 CFU.cm-2, resulting

to a multiplicity of infection (MOI) of 100. Infected cells were then incubated at 37°C in 5% CO2-95% air during 24 h for all experiments, excepted 4 h of infection for the invasion test. Each assay was conducted in triplicate in independent experiments (successive passages of Caco-2/TC7 cells). Cytotoxicity assay Cytotoxicity assay was performed on confluent Caco-2/TC7 grown in 24-wells culture plates. After 24 h of infection, the supernatants from Caco-2/TC7 monolayers were collected and the concentration of lactate dehydrogenase (LDH), a cytoplasmic enzyme released upon cell death, was determined

using an enzymatic assay (Cytotox 96 Promega, Charbonnieres, France) as previously described [17]. Caco-2/TC7 cells exposed to Triton ×100 (0.9%) were used as a control of total LDH release (100% dead cells). Bacterial invasion assay After 4 h of infection, Caco-2/TC7 monolayers were washed with phosphate-buffered saline (PBS). Adherent bacteria were killed by incubation for 1 h with 300 μg.mL-1 gentamycin, an antibiotic that does not cross the cytoplasmic membrane of eukaryotic cells and then only kills bacteria not internalized in cells. Caco-2/TC7 monolayers were washed 3 times with PBS to remove the antibiotic and dead bacteria. The Selleck VX-680 cells were then lysed by incubation for 15 min with 0.5% Triton ×100 to release the intracellular bacteria and the lysates were plated onto nutrient agar to determine the number of internalized bacteria. Quantification of IL-6, IL-8 and HBD-2 After 24 h of infection with the bacterial suspensions, the levels of IL-6 and IL-8 cytokines were measured in Caco-2/TC7 cells supernatant using ELISA Quantikine kits (R&D systems). The human β-defensin-2 (HBD-2) was quantified using the Defensin 2, beta (Human) – ELISA Kit (Phoenix Pharmaceuticals Dichloromethane dehalogenase inc). These assays were conducted

according to the manufacturer’s protocols. Transepithelial electrical resistance measurements Caco-2/TC7 cells grown on inserts were used at 21 days post-confluence (fully differentiated cells) and the transepithelial electrical resistance (TER) of the monolayers infected or not with the bacterial strains was measured during 24 h using the Millicell Electrical Resistance System (Millipore Corp, Bedford, MA). TER values are expressed as percentages of the pre-infection level of the TER (baseline) measured for each click here individual cell monolayer in the inserts. Actin visualisation Fully differentiated Caco-2/TC7 monolayers were exposed to the bacterial strains for 24 h. At the end of the experiment, the cells were washed with PBS, fixed for 10 min in 3.7% paraformaldehyde and permeabilized for 5 min with 0.1% Triton ×100 at room temperature.