Intestinal transit time and the gut microbiota: causality and implications?

Microbial communities are highly dependent on the abiotic (environmental) factors of their surroundings, which affect both the composition and activity of the communities. However, our understanding of how specific abiotic factors of the gut affect the gut microbial community is limited. In the collaborative project named PRIMA (towards Personalized dietary Recommendations based on the Interaction between diet, Microbiome, and Abiotic conditions in the gut), we strive to understand how selected abiotic factors in the gut affect the microbiome and thereby host health. A key environmental factor of the gut is intestinal transit time. This factor is subject to high interindividual variability even in healthy subjects, and we  hypothesize that it may drive differences in gut microbial composition and responses to different diets. Moreover, the extremes of intestinal transit times (i.e., constipation and diarrhea) accompany various medical conditions, including inflammatory bowel diseases, Parkinson’s disease, and autism spectrum disorders. Thus, understanding the relationship between intestinal transit time and the gut microbiota may improve our understanding of microbiota/host interactions in health and disease.

We will present the concept and preliminary results from two pilot mouse studies, both focusing on the establishment of animal models for manipulated intestinal transit time. In the first pilot study, we demonstrated that suspensions of Imolope tablets (loperamide), increased intestinal transit time in conventional C56BL/6 mice in a dose-dependent manner. In the second pilot study, we transferred fecal material from two healthy human donors, one with short and one with long transit time, to germ-free Swiss Webster mice. After fecal transplantation, no difference in transit time between the two groups was observed. Thus, in our experimental setup, transit time could not be transferred through fecal transplantation, and we will continue working with the model of pharmaceutical manipulation of transit time in our future animal experiments.