Human gastrointestinal tract resistance of Lactobacillus strains isolated from infant faeces

Resumen

The probiotic bacteria survival during the gastrointestinal transit is primordial, and implies in the ability of microorganisms to survive at the stomach acidity and bile, so they can exert their beneficial effects on the host. The aim of this study was to evaluate, “in vitro”, Lactobacillus strains originated from one year old children fecal material in the selection of probiotic microorganisms. Two commercial strains, L. casei (Lc 01^TM) and L. acidophilus (La-05 ^TM) were used as controls. The first screening resulted in 75 colonies and they were isolated from six samples faeces. Isolates were Gram positive, mostly rod shaped (cocobacilli, long and thin rods) and rarely cocci. They were submitted to catalase test and evaluated for the presence of spores, resulting in 30 pre-selected strains. Among those strains, eight strains: L4, L5, L12, L19, L20, L22, L23, L24 were the most resistant to Oxgall (bile salts) concentration (0.3 w/v). These eight strains were also resistant to acid conditions (pH 3.0) and all strains were able to grow in the presence of 0.3 w/v of phenol. The results of treatments were compared to the Neuman Keuls Student test at 5% of probability, with regression analyses made at different times for tolerance to intestinal conditions. The results demonstrated that all these strains were able to survive under gastrointestinal stress condition, indicating potential use as probiotics. The high survival rate of probiotic strains, in conditions that simulate the gastrointestinal transit, is strain dependent and thus, a proper selection of strains in the development of dairy probiotic products is vital.