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There is a long history of health claims concerning living microorganisms in food. Already the Persian version of the Old Testament states that ‘Abraham owed his longevity to the consumption of sour milk.’ However, it was only at the beginning of last century that the health effects associated with the intake of fermented products (i.e. yoghurt) were for the first time linked to a shift in the intestinal microbial balance. Since then, the interest in gastrointestinal microbiota modulation has significantly increased, generating the idea that human health can be enhanced, and the risk of disease reduced by the consumption of health-promoting bacteria such as probiotics. Currently, probiotics are considered as ‘living microorganisms which, when administered in adequate amounts, confer a health benefit on the host.’ Although detailed molecular mechanisms underlying probiotic action are largely unknown, adhesion of these microorganisms, including lactobacilli, to the intestinal mucosa is considered one of the main properties to confer health effects. Despite the fact that Lactobacillus rhamnosus GG (LGG) is one of the clinically most studied probiotic organisms, and which selection as probiotic strain is mainly based on its ability to adhere to the intestinal mucosa, the molecular mechanisms mediating the adhesion of this strain are largely unstudied. In this work, a search for these factors was initiated. Both, a membrane-associated protein and the non-proteinaceous lipoteichoic acids (LTA) were studied in detail in relation to their role in LGG adhesion and host stimulation. During the last years the number of probiotic-containing food products introduced in the market has witnessed a strong increase. A microbiological analysis of seven bio-yoghurts available at the Columbian market was performed. Based on the results, some of the isolates were classified as potential probiotic strains, based on a comparison with LGG. However, not all of them were present in the advised amount to exert beneficial health effects. In addition to the consumption of probiotic-containing products, the consumption of food ingredients such as prebiotics is thought to provide beneficial effects in the gastrointestinal tract of humans and animals. Prebiotics are non-digestible food ingredients that benefit the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon. In this work, the prebiotic potential of a specific non-digestible oligosaccharide was evaluated for LGG. Results indicated that although LGG is not able to ferment the tested compound as such, it plays an important role, be it most likely indirectly, in the modulation of important LGG metabolic pathways. Moreover, preliminary evaluation of the capacity of the non-digestible oligosaccharide indicated its possible potential as anti-inflammatory compound.

Academic collection --- 579.264 --- 577.2 --- 579.864 --- 579.864 Lactobacillaceae. Lactobacillus --- Lactobacillaceae. Lactobacillus --- 577.2 Molecular bases of life. Molecular biology --- Molecular bases of life. Molecular biology --- 579.264 Antagonism. Probiotics --- Antagonism. Probiotics --- Theses