Microbiome diversity predicts surgical success in patients with rectovaginal fistula.

INTRODUCTION AND HYPOTHESIS: Growing literature details the critical importance of the microbiome in the modulation of human health and disease including both the gastrointestinal and genitourinary systems. Rectovaginal fistulae (RVF) are notoriously difficult to manage, many requiring multiple attempts at repair before correction is achieved. RVF involves two distinct microbiome communities whose characteristics and potential interplay have not been previously characterized and may influence surgical success. METHODS: In this pilot study, rectal and vaginal samples were collected from 14 patients with RVF. Samples were collected preoperatively, immediately following surgery, 6-8 weeks postoperatively and at the time of any fistula recurrence. Amplification of the 16S rDNA V3-V5 gene region was done to identify microbiota. Data were summarized using both α-diversity to describe species richness and evenness and ß-diversity to characterize the shared variation between communities. Differential abundance analysis was performed to identify microbial taxa associated with recurrence. RESULTS: The rectal and vaginal microbiome in patients undergoing successful fistula repair was different than in those with recurrence (ß-diversity, p = 0.005 and 0.018, respectively) and was characterized by higher species diversity (α-diversity, p = 0.07 and p = 0.006, respectively). Thirty-one taxa were enriched in patients undergoing successful repair to include Bacteroidetes, Alistipes and Rikenellaceae as well as Firmicutes, Subdoligranulum, Ruminococcaceae UCG-010 and NK4A214 group. CONCLUSIONS: Microbiome characteristics associated with fistula recurrence have been identified. The association of higher vaginal diversity with a favorable outcome has not been previously described. Expansion of this pilot project is needed to confirm findings. Taxa associated with successful repair could be targeted for subsequent therapeutic intervention.