Anticancer impacts of potentially probiotic acetic acid bacteria isolated from traditional dairy microbiota

Two acetic acid bacteria, Acetobacter indonesiensis and Acetobacter syzygii, were isolated from Iranian traditional yogurt and curd, respectively, and were identified by using Basic Local Alignment Search Tool search of their amplified 16S rRNA gene sequences. Several primary tests were conducted on isolated bacteria, including Gram staining, catalase assay, low pH and high bile salt concentration tolerance, antibacterial activity against pathogenic bacteria, and antibiotic susceptibility, to prove the probiotic properties of isolates. Strain secretions were also used for cytotoxicity assessments on several cancer cell lines (HeLa, MCF-7, AGS, and HT-29) and a human normal cell line (human umbilical vein endothelial cells) through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay as well as qualitative and quantitative evaluations of apoptosis. The results proved the acceptable probiotic characteristics of the isolated strains. A. syzygii secretions showed significant cytotoxicity against all cancer cell lines, whereas these secreted metabolites did not show cell toxicity on human normal cells. In conclusion, the anticancer effect of A. syzygii strain secretions depends on the induction of apoptosis in cancer cells. However, several investigations should be conducted to precisely determine the effective compounds to be used as anticancer therapeutics in the future.