Effect of a Probiotic Bile Salt Hydrolytic Lactobacillus reuteri on the Human Gastrointestinal Microbiota as Simulated in the SHIME Reactor System

Abstract

The SHIME reactor (Simulator of the Human Intestinal Microbial Ecosystem) was used to evaluate the use of a bile salt hydrolytic (BSH⁺) Lactobacillus reuteri strain as a probiotic. The effect of L. reuteri on representative microbial associations and on the overall metabolic activity of the SHIME microbiota was investigated. Administration of L. reuteri resulted in a decrease of the Enterobacteriaceae and coliform populations of more than 1 log unit. The CO₂ production decreased by 25-40%, while the concentration of volatile fatty acids augmented by 20-30%. The NH₄⁺ concentration increased during the treatment period from 400 mg N-NH₄⁺/l to about 500 mg/l. Since at the same time the concentration of extracellular protein increased by 25-30%, the ratio of extracellular protein on NH₄⁺ increased, mostly in reactor 4 (36%; p<0.05) and 5 (31%; p<0.05) and less in reactor 6. These effects disappeared when the strain was no longer administered. The strain produced no reuterin so that other bacteriocin-like compounds were probably responsible for the observed inhibitions. The strain showed satisfying survival capacities during passage through the stomach (at most factor 10 die-off) and could maintain growth in the presence of high levels of bile salts. These results suggest that L. reuteri can qualify as an organism to be administered orally to affect the gastrointestinal microbial ecology.