An exploratory journey into probiotic interactions : Bioactive properties of Limosilactobacillus reuteri and Bifidobacterium longum

Abstract

Probiotics are defined as live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. The mechanisms by which probiotics affect the host are based on one of two principles: i) directly, by interacting with specific targets, or ii) indirectly, by contributing to the ecological niche constructions of the microbiota. This thesis examined how probiotic bacteria interact with each other and with the host, and how production of probiotics can be manipulated to increase biological functionality, ultimately benefiting the host. Limosilactobacillus reuteri DSM 17938 is a well-documented probiotic strain, but the mechanisms by which it alleviates infantile colic, combats inflammation, and interacts with the immune system are not well understood. However, several features related to the bioactive properties of DSM 17938 may partly explain these interactions. The features in question are extracellular membrane vesicles (MV), exopolysaccharides (EPS), enzymes, and other metabolites. MV and EPS were evaluated in different models of host interactions, aimed at reflecting possible mechanisms of action in infantile colic. Multifunctionality among the MV was demonstrated and it was also shown that the amount and activity of bioactive components can be altered by optimizing production parameters. Further, a novel strain of Bifidobacterium longum subsp. longum was described and shown to be a potent fiber degrader, able to stimulate growth and bioactivity of DSM 17938 and its MV in vitro. Bifidobacteria and lactobacilli are important in ecological niches of the human gut and the interactions between these bacteria may be key to understanding how to fight inflammatory diseases and disorders using probiotics.