The acid and bile tolerance of the isolates were determined as described previously by Ben Salah et al. The cultures were
grown in MRS broth at 37 ◦C overnight. The cultures were centrifuged at 2000 × g for 10 min at 4 ◦C. The pellets were washed twice in sterile phosphate-buffered saline (PBS, pH 7·2) and resuspended in MRS broth. For each isolate the culture suspension (0.1 at OD600 nm) was added separately into series of tubes containing 2 ml of MRS broth at various pH of 3–5. Three tests, each with a duplicate was made for each isolates at each pH value. The OD600 nm was recorded every 1 h for 8 h. Bile tolerance was estimated using the same procedure except the isolates were inoculated in MRS broth containing bovine bile (1% and 5%). The MRS broth without bile served as a control.