In vitro Probiotic Potential and Anti-cancer Activity of Newly Isolated Folate-Producing Streptococcus thermophilus Strains

Abstract

Most probiotic strains commercially available today are lactic acid bacteria. Within this functional group, <i>Streptococcus thermophilus</i> is a thermophilic species widely used as starter culture for a huge number of dairy products. Besides being rapid acidifiers, many <i>S. thermophilus</i> strains are able to produce and release folate during growth but, unfortunately, they are seriously impaired during passage through the human gastrointestinal tract. In this work, we studied eight <i>S. thermophilus</i> strains isolated from dairy environments in Italy, which already had shown good technological properties, to evaluate their possible probiotic potential and cytotoxicity against cancer cells <i>in vitro</i>. All strains were also evaluated for some health-related properties such as susceptibility to most common antibiotics, hemolytic activity, resistance to simulated gastrointestinal conditions, bile salts hydrolytic activity, production of folate, adhesion to HT-29 human colorectal adenocarcinoma cells and cytotoxic activity against cancer cells and production of biogenic amines. Results revealed that two fast acidifying <i>S. thermophilus</i> strains were found to possess <i>in vitro</i> probiotic properties along with anticancer activity and production of folate. These properties resulted similar and, in some cases, superior to those of <i>Lactobacillus rhamnosus</i> GG, a well-known commercial probiotic strain. These findings encourage further <i>in vivo</i> studies to evaluate the actual health benefits of these strains on the human host.