Intestinal transit time phenotype is not transferred through gut microbiota transplantation

Intestinal transit time (TT) varies considerably between healthy individuals and affects gut microbiota composition and activity. Whether differences in the gut microbiota composition also affect the TT is not well elucidated. In this study, we conducted two animal experiments to explore causality between the gut microbiota and TT. In the first experiment, we transplanted two groups of female germ-free (GF) Swiss-Webster mice with fecal material from two healthy human donors with fast and slow TT phenotypes. Following transplantation with human feces, we observed a decrease in TT for both groups of GF recipient mice (from 300 min to 167 min, 95% CI: ±45; and from 369 vs 205 min, 95% CI: ±52) corresponding to reductions of approximately 45% in each group, supporting previous findings that the mere presence of a gut microbiota reduces TT. However, we found no differences in TT between the two recipient groups. In the second experiment, we transplanted two groups of female GF C57Bl/6J mice with cecal material from two different conventional C57Bl/6J mouse donor groups treated with the TT-increasing drug loperamide or a saline vehicle. Again, no differences in TT were observed between the two recipient groups. These findings indicate that either the transferred microbiota did not engraft effectively, or that gut microbiota composition itself is not the principal driver of inter-individual TT variation.