Effects of Lactobacillus plantarum A7 with probiotic potential on colon cancer and normal cells proliferation in comparison with a commercial strain

Several beneficial effects have been attributed to the probiotic lactic acid bacteria. It was determined that lactobacilli can exert antiproliferative effects on the various cancer cell lines including colon cancer. Effects of lactic acid bacteria on colon cancer may vary from strain to strain and there is a need to find the new probiotic strains with tumor suppressing properties through in vitro studies. Anti-proliferative activities of heat-killed cells and cell-free supernatants of a native strain of Lactobacillus plantarum A7 and a commercial strain of lactobacillus rhamnosus GG were assessed on human colon cancer cell lines (Caco-2 and HT-29) and normal cells (L-929), using MTT assay. Cells were seeded at 2×104 cells/mlin 96 well plates and incubated for 24 hr. Then heat-killed cells (OD620: 0.025, 0.0.05, 0.1) and cell-free supernatants of bacteria were added at concentration of 2.5, 5 and 10 mg/ml. After 48 hr incubation MTT (5 mg/ml) was added and the absorbance was measured at 540 nm using ELISA plate reader. Results showed that heat-killed cells and cell-free supernatants of both probiotic strains reduced the growth rate of cancer and normal cells. These results suggested that anti-proliferative effect may not be an exclusive characteris ticwhich is dedicated to officially approved probiotics. L. plantarum A7 could be considered as colon cancer biological product, most likely due to its advantages in significant organic acid production.