Abstract: To investigate the proliferation effect of exopolysaccharide(EPS)produced from Streptococcus thermophilus of Tibetan kefir on human colon cancer HCT-8 cells. CCK-8 assay was used to examine the effect of EPS in anti-proliferation, killing effect of EPS was evaluated through morphology identification combined with fluorescence microscopy observation, the cell cycle pattern was studied by flow cytometry. CCK-8 assay showed that the proliferation of HCT-8 cells was inhibited apparently after treatment with EPS, and in a time- and dose-dependent manner. EPS treatment resulted in morphological changes, including cell shrinkage, membrane blebbing, nuclear condensation, boundary aggregation or split, the necrotic cells increased along with the elevation of EPS concentration, and leading to cell cycle arrest at G1 phase. EPS showed that its anti- tumer effect by way of direct killing effects and make cells arresting the G1 phase to inhibiting the cell growth.

Key words: Streptococcus thermophilus, exopolysaccharide, human colon cancer cells, anti-proliferation, cell cycle