Lactobacillus reuteri (now renamed to Limosilactobacillus reuteri) is a species of bacteria that belongs to one of the major lactic-acid producing genera of bacteria. It can be found in the human intestinal tract, though not always and often in relatively low numbers. Lactobacillus reuteri is also found in the gut of other mammals and birds.
Initially, Lactobacillus reuteri was used to treat necrotizing colitis, a gastrointestinal disease characterized by infection and inflammation that is particularly dangerous for infants, particularly those born prematurely. Lactobacillus reuteri was used due to its anti-inflammatory effects. The research on Lactobacillus reuteri and necrotizing colitis used the Lactobacillus reuteri strains ATCC 55730 and its daughter strain DSM 17938, both of which can survive oral supplementation.
Interest in Lactobacillus reuteri grew after research confirmed that changing aspects of the digestive system can influence the immune system. A strain of Lactobacillus reuteri called ATCC PTA 6475 has been found to improve levels of testosterone and oxytocin, as well as skin quality in animal studies. Research on animals has also found potential benefits for hair quality, bone mass and preventing weight gain from obesity-causing diets.
One of the ways Lactobacillus reuteri may work involves a kind of T cell called a Treg cell (a T cell that down-REGulates the immune system in part by producing a cytokine called IL-10). Lactobacillus reuteri increases the amount of Treg cells in the body, which suppresses the actions of another kind of T cell called a Th17 cell (which secretes IL-17). Preserving or reversing this process (either by increasing IL-10 or by blocking IL-17) appears to provide therapeutic benefits.
Lactobacillus reuteri increases the number of Treg cells in the intestines, which can then be absorbed back into the blood to benefit the rest of the body.