Bacteroides fragilis derived metabolites, identified by molecular networking, decrease Salmonella virulence in mice model

Thomas Gautier; Nolwenn Oliviero; Solenn Ferron; Pierre Le Pogam; Sandrine David-Le Gall; Aurélie Sauvager; Patricia Leroyer; Isabelle Cannie; Sarah Dion; Alaa Sweidan; Olivier Loréal; Sophie Tomasi; Latifa Bousarghin

doi:10.3389/fmicb.2022.1023315

Bacteroides fragilis derived metabolites, identified by molecular networking, decrease Salmonella virulence in mice model

Front Microbiol. 2022 Nov 10:13:1023315. doi: 10.3389/fmicb.2022.1023315. eCollection 2022.

Affiliations

¹ INSERM, Univ Rennes, INRAE, UMR 1241, Nutrition Metabolisms and Cancer Institute, Rennes, France.
² Univ Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) - UMR 6226, Rennes, France.
³ BioCIS, Université Paris-Sud, CNRS, Université Paris-Saclay, Châtenay-Malabry, France.
⁴ Univ Rennes, INSERM, EHESP, Irset (Institut de recherche en santé, environnement et travail) - UMR_S 1085, Rennes, France.
⁵ Laboratory of Microbiology, Department of Life and Earth Sciences, Faculty of Sciences I, Lebanese University, Hadath Campus, Beirut, Lebanon.

Abstract

In the gut microbiota, resident bacteria prevent pathogens infection by producing specific metabolites. Among bacteria belonging to phylum Bacteroidota, we have previously shown that Bacteroides fragilis or its cell-free supernatant inhibited in vitro Salmonella Heidelberg translocation. In the present study, we have analyzed this supernatant to identify bioactive molecules after extraction and subsequent fractionation using a semi-preparative reversed-phase Liquid Chromatography High-Resolution Tandem Mass Spectrometry (LC-HRMS/MS). The results indicated that only two fractions (F3 and F4) strongly inhibited S. Heidelberg translocation in a model mimicking the intestinal epithelium. The efficiency of the bioactive fractions was evaluated in BALB/c mice, and the results showed a decrease of S. Heidelberg in Peyer's patches and spleen, associated with a decrease in inflammatory cytokines and neutrophils infiltration. The reduction of the genus Alistipes in mice receiving the fractions could be related to the anti-inflammatory effects of bioactive fractions. Furthermore, these bioactive fractions did not alter the gut microbiota diversity in mice. To further characterize the compounds present in these bioactive fractions, Liquid Chromatography High-Resolution Tandem Mass Spectrometry (LC-HRMS/MS) data were analyzed through molecular networking, highlighting cholic acid (CA) and deoxycholic acid. In vitro, CA had inhibitory activity against the translocation of S. Heidelberg by significantly decreasing the expression of Salmonella virulence genes such as sipA. The bioactive fractions also significantly downregulated the flagellar gene fliC, suggesting the involvement of other active molecules. This study showed the interest to characterize better the metabolites produced by B. fragilis to make them means of fighting pathogenic bacteria by targeting their virulence factor without modifying the gut microbiota.

Keywords: Bacteroides fragilis; cholic acid; fractionation; metabolites; microbiota; molecular networking; supernatant; virulence factors.