Exopolysaccharides May Increase Gastrointestinal Stress Tolerance of Lactobacillus reuteri

This study investigated a possible relationship between exopolysaccharides (EPS) production and the resistance to bile salts and low pH in intestinal strains of Lactobacillus reuteri. The strains displayed a mucoid phenotype, when grown in the presence of 10 % sucrose. Scanning electron microscopy (SEM) revealed strands of exopolysaccharide linking neighbouring cells. The strains (except L. reuteri B1/1) produced EPS in the range from 15.80 to 650.70 mg.l−1. The strains were tested for tolerance to bile salts (0.15; 0.3 %) and low pH (1.5—2.0—2.5—3.0). The survival rate, after the treatment with artificial gastric and intestinal juices, was determined by flow cytometric analysis. The strains of L. reuteri that produced 121—650 mg.l−1 of EPS showed a significantly higher tolerance (P < 0.001) to the gastric juice at pH 3 and 2.5, throughout the entire exposure time, in comparison to the strains that produced less than 20 mg.l−1 of EPS. L. reuteri L26, with the highest production of EPS, exhibited the highest survival rate (60 %) at pH 2 after the 120 minutes of in-cubation and was able to tolerate pH 1.5 for 30 minutes. Higher production of EPS significantly (P < 0.001) increased the strains’ tolerance against the intestinal juice in the presence of 0.15 and 0.3 % bile salts and was time dependent. L. reuteri L26 showed the highest tolerance (P < 0.001) against 0.3 % bile salts. This investigation revealed a positive correlation between the EPS production and the resistance of intestinal L. reuteri to the stress conditions of the gastrointestinal tract (GIT).