Effect of acquired resistance to bile salts on enzymatic activities involved in the utilisation of carbohydrates by bifidobacteria.: An overview

Bifidobacteria are probiotics widely used in dairy-based products. In order to exert the health-promoting benefits attributed to these microorganisms, they must survive the restrictive conditions of the gastrointestinal tract, being resistant, among other factors, to the toxic action of bile salts. The inhibition exerted by these compounds on bifidobacteria can be overcome by progressive adaptation to gradually increasing concentrations of bile. The acquisition of stable resistance, or even transient exposure to bile salts in Bifidobacterium, promoted in these microorganisms irreversible physiological changes that are reviewed in this article. The presence of, or short-term exposure to bile salts caused a diminution in adhesion to mucus and intestinal epithelial cells, as well as a decrease in cellular surface hydrophobicity. However, adaptation to high bile salt concentrations promoted an enhancement of adhesion to intestinal mucus, which correlates in some cases with increases in cellular surface hydrophobicity. In addition, differences in membrane protein profiles, better tolerance to low pH, and variations in glycosidic activities and fructose-6-phosphate-phosphoketolase (F6PPK) activity were detected in some bile-adapted strains with respect to their originals. In particular, some bile-resistant derivatives showed higher levels of F6PPK activity than the corresponding more sensitive strains of origin, and increases in alpha-glucosidase and beta-glucosidase activities. These glycosidases are responsible for the hydrolysis of maltose and cellobiose, respectively. Both disaccharides can result from the partial hydrolysis of glucose polysaccharides. The more detailed study of one original/resistant derivative pair indicated that the acquisition of bile salt resistance maintained the viability of old cultures and promoted shifts in the carbohydrate fermentation patterns, which modified growth in media containing maltose or glucose as a carbon source, as well as the profile of organic acids formed. Bile tolerance adaptative mechanisms may lead to better adaptation to the colon environment and available carbon sources as well as to an increase in the viability and permanence of Bifidobacterium in the intestinal environment.