Safety assessment of Butyricicoccus pullicaecorum

Advances in gut microbiota research have triggered interest in developing colon butyrate producers as niche-specific next-generation probiotics, targeted at increasing colon butyrate production and countering disease-associated microbiota alterations. Crucial steps in the development of next-generation probiotics are the design of formulations with a reasonable shelf life as well as the safety demonstration of an intervention in healthy volunteers. One such potential next-generation butyrate-producing probiotic is Butyricicoccus pullicaecorum 25-3T, with demonstrated safety in in vitro as well as in animal models. Here, we examined the strain's safety, tolerability, and impact on microbiota composition and metabolic activity in healthy volunteers in a randomized, double blind, placebo-controlled, crossover study in 30 healthy volunteers. Study design consisted of two four-week intervention periods (108 CFU B. pullicaecorum [treatment] or maltodextrin [placebo] per day) with a three-week washout in between. We assessed adverse events, blood parameters (primary endpoints), and fecal microbiota composition and metabolite profiles (secondary endpoints).The number of reported adverse events during the B. pullicaecorum treatment was similar to placebo intervention, as were observed changes in blood chemistry parameters, bowel habits, and fecal calprotectin concentrations. Administration of the strain did not induce any disruptive effect in microbiota composition or metabolic activity. In this first human intervention trial with a butyrate-producing Clostridium cluster IV isolate, we demonstrated B. pullicaecorum 25-3T administration to be both safe and well tolerated by healthy participants. This safety study paves the way for the further development of the strain as a next-generation probiotic.