Bacterial strains, cell lines and culture conditions L. plantarum was grown at 30uC in LM medium [1% proteose peptone (w/v), 1% beef extract (w/v), 0.5% yeast extract (w/v), 0.5% lactose (w/v), 9 mM ammonium citrate, 61 mM sodium acetate anhydrous, 0.4 mM magnesium sulfate, 0.3 mM manganese sulfate, 11.2 mM dipotassium phosphate, 0.5% Tween 20 (v/ v)], supplemented with 10 mg/ml of chloramphenicol (Cm). E. coli was grown at 37uC in TBY medium (BD, Franklin Lakes, NJ). T84 human colonic carcinoma epithelial cells were obtained from the American Type Culture Collection (ATCC, CCL-248, Manassas, VA). T84 cells were maintained at 37uC, 5% CO 2 in DMEM-F12K medium modified by ATCC, containing 10% FCS, 100 U/ ml penicillin and 100 mg/ml streptomycin.