THE INFLUENCE OF INDIGENOUS SEGMENTED FILAMENTOUS BACTERIA ON SMALL-INTESTINAL TRANSIT IN MICE

The indigenous microbiota of healthy animals is known to stimulate int estinal motility. Since the indigenous microbiota of the ileum dominan tly contains segmented filamentous bacteria (SFB), we tested the hypot hesis that SFB are involved in increasing small intestinal transit (SI T). Five groups of mice were compared: germfree mice, mice mono-associ ated 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 charc oal 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 mon o-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 s econd group served as a control. Although SFB were successfully remove d, their stimulating influence on SIT could not be reversed. Increased intestinal transit had a positive effect on the clearance of an admin istered non-pathogenic Escherichia coli TG1. However, no difference wa s found in the clearance of Morganella morganii, a mild pathogen that is able to translocate to peripheral sites. We conclude that SFB stimu late SIT which leads to an increased clearance of some bacterial speci es while others might show mechanisms to escape from such a clearance.