2.9. MTT assay
Cancer/normal cell lines (with cell density of 1.2 104 cell/well)
were seeded into each well of the 96-well microplates (Nunc,
Denmark) and incubated under cell growth conditions. According
to the adequate number of viable probiotic cells for fresh dairy
products (1e10 106 CFU/ml), 10 concentration rates (5 mg/ml to
50 mg/ml) were screened on four cancer cell lines. Different concentrations
of sterile bacterial secretions, pronase (Roche Applied
Science) treated/untreated secretions, were administrated into
each well after post-seeding for 24 h. Treated/untreated cell lines
were incubated for 48 h. The medium of each well after incubation
was replaced with equally fresh media containing 20 ml of MTT
solution (2 mg/ml). Incubation was continued under dark conditions
for 4 h. The medium of each well was again replaced with
200 ml DMSO plus 25 ml of Sorenson's glycine buffer (0.1 Mglycine,
0.1 M NaCl, pH 10.5) and incubated for 30 min at 37 C. The
absorbent of microplates were read using m Quant ELISA Reader
(Bio-tek Instruments, USA) at 570 nm. Taxol, as a famous anticancer
drug, was used as a positive control in this assessment