The Influence of Indigenous Segmented Filamentous Bacteria on Small Intestinal Transit in Mice

The indigenous microbiota of healthy animals is known to stimulate intestinal motility. Since the indigenous microbiota of the ileum dominantly contains segmented filamentous bacteria (SFB), we tested the hypothesis that SFB are involved in increasing small intestinal transit (SIT). Five groups of mice were compared: germfree mice, mice mono-associated either with SFB or with Clostridium innocuum , SFB-free mice with a specified pathogen-free (SPF) microbiota and SFB-positive SPF mice. As a measure for intestinal transit, the distance travelled by a charcoal marker was determined 30 min after oral administration. We found a strong increase in SIT in both the mice mono-associated with SFB, and the SFB-positive SPF mice (P<0.05), but not in SPF mice or mice mono-associated with C. innocuum when compared to germfree mice. SPF-mice with and without SFB were given ciprofloxacin for either 3 or 13 d to remove SFB from the intestinal tract from the first group while the second group served as a control. Although SFB were successfully removed, their stimulating influence on SIT could not be reversed. Increased intestinal transit had a positive effect on the clearance of an administered non-pathogenic Escherichia coli TG1. However, no difference was found in the clearance of Morganella morganii , a mild pathogen that is able to translocate to peripheral sites. We conclude that SFB stimulate SIT which leads to an increased clearance of some bacterial species while others might show mechanisms to escape from such a clearance. Keywords: segmented filamentous bacteria, microbiota, Clostridium innocuum , small intestinal transit; mice.