Briefly, autoclaved (15 min at 121 °C) or non-heated CFS diluted in DMEM with 2% methanol were added to each well of Hep-2 cells and incubated 24 h at 37 °C in 5% CO2. CFS (autoclaved or non-heated) from a ces (−) B. cereus strain (B10502) were also evaluated. The medium was removed and DMEM (without phenol red) containing 0.5 mg/ml of MTT was added to each well; plates were incubated at 37 °C for 4 h and then, the medium was removed. Intracellular formazan was solubilized with 0.25 ml of isopropyl alcohol/0.1 N HCl and absorbance at 570 nm was measured in a microtiter plate reader (Bioteck Instruments, Winooski, USA).