It has been well-established that the gut microbiota, the indigenous microbes of the gastrointestinal tract, is intimately involved in susceptibility to colonization and infection with Clostridium difficile, an important health care-associated pathogen. Alteration of these microbes, such as after antibiotic use, can result in the depletion of key microbial functions that provide resistance to C difficile infection (CDI).1,2 Given the success of fecal microbiota transplantation in treating CDI, considerable effort has been made to develop targeted microbial treatments.