Outer Membrane Vesicles Secreted by Bacteroides fragilis Inhibit CFTR Chloride Secretion by Human Colon Organoids

The goals of this study were to develop a model to study host pathogen interactions in primary human colon organoids and to test the hypothesis that Bacteroides fragilis toxin (BFT-2) secreted in outer membrane vesicles (OMVs) modulates mucosal immunity and CFTR Cl ^- secretion. Since Bacteroides species reside in mucus, OMVs are likely to represent a mechanism of communication between Bacteroides and the host. Two strains of Bacteroides were studied, Enterotoxigenic Bacteroides fragilis (ETBF), which produces BFT-2, and the non-toxigenic Bacteroides fragilis strain NCTC 9343 (NTBF) that does not produce BFT-2. We also utilized two additional strains of Bacteroides fragilis: one in which bft -2 was knocked out (ETBF Δ bft ), and one that was engineered to contain bft-2 (NTBF+ bft) . We report that Bacteroides fragilis OMVs reduced CFTR Cl ^- secretion but had no effect on tight junction or cell adhesion proteins, transepithelial resistance (TER) or cytokine secretion by primary human colon organoids. NTBF OMVs containing BFT-2 were more effective in reducing CFTR Cl ^- secretion than NTBF lacking BFT-2. We conclude that OMVs secreted by Bacteroides can be an important mechanism of host pathogen interactions in the colon by reducing CFTR Cl ^- secretion.