Defined microbial communities and their soluble products protect mice from Clostridioides difficile infection

Clostridioides difficile is the leading cause of antibiotic-associated infectious diarrhea. The development of C.difficile infection is tied to perturbations of the bacterial community in the gastrointestinal tract, called the gastrointestinal microbiota. Repairing the gastrointestinal microbiota by introducing lab-designed bacterial communities, or defined microbial communities, has recently shown promise as therapeutics against C.difficile infection, however, the mechanisms of action of defined microbial communities remain unclear. Using an antibiotic- C.difficile mouse model, we report the ability of an 18-member community and a refined 4-member community to protect mice from two ribotypes of C.difficile (CD027, CD078; p < 0.05). Furthermore, bacteria-free supernatant delivered orally to mice from the 4-member community proteolyzed C.difficile toxins in vitro and protected mice from C.difficile infection in vivo (p < 0.05). This study demonstrates that bacteria-free supernatant is sufficient to protect mice from C.difficile; and could be further explored as a therapeutic strategy against C.difficile infection.