Bacteroides vesicles promote functional alterations in gut microbiota composition

Inflammatory bowel diseases are characterized by chronic intestinal inflammation and alterations of gut microbiota composition. Bacteroides fragilis, which secretes outer membrane vesicles (OMVs) with polysaccharide A (PSA), can moderate inflammatory response and possibly alter microbiota composition. In this research, we created a murine model of chronic DSS- induced intestinal colitis and treated it with Bacteroides fragilis OMVs. We monitored the efficiency of OMVs therapy by determining the disease activity index (DAI) and histological examination (HE) of the intestine before and after vesicles exposure. We also analyzed the microbiota composition using 16S rRNA gene sequencing. Finally, we evaluated the volatile compounds composition in animals stools by HS-GC/MS to assess the functional activity of the microbiota. As a result, we observed a more effective intestine repair after OMVs treatment according to DAI and HE. The metabolomic study also indicated the microbiota functional activity change, showing a predominance of phenol and pentanoic acid in the control group compared to the group treated with DSS (DSS) and the group treated with OMVs (DSS OMV). We also observed a positive correlation of these metabolites with Saccharibacteria and Hungatei Clostridium in the control group, whereas in the DSS group there was a negative correlation of phenol and pentanoic acid with Lactococcus and Romboutsia. According to metabolome and sequencing data, the microbiota composition of the DSS OMV group was intermediate between the control and DSS groups. It can be concluded that OMVs not only have an anti-inflammatory effect, but also contribute to the recovery of the microbiota composition.