OBJECTIVES: The intestinal microbiota plays an important role in intestinal health. After colonic diversion from the fecal stream, luminal nutrients for bacteria are expected to be depleted, inducing changes in microbial composition. In this study, we describe microbial changes in the healthy colon following surgical fecal stream diversion, studied in the surgically constructed sigmoid-derived neovagina. METHODS: At various postoperative times after sigmoid vaginoplasty, rectal, neovaginal, and skin microbial swabs were obtained for microbial analysis by interspacer profiling, a PCR-based bacterial profiling technique. Differences in bacterial profiles, in terms of bacterial abundance and phylum diversity, were assessed. Microbial dissimilarities between anatomical locations were analyzed with principal coordinate analysis and partial least squares discriminant analysis. RESULTS: Bacterial samples were obtained from 28 patients who underwent sigmoid vaginoplasty. By principal coordinate analysis, microbial profiles of samples from the sigmoid-derived neovagina were distinctively different from rectal samples. Partial least squares discriminant analysis showed that the most discriminative species derived from the phylum Bacteroidetes. The abundance and diversity of Bacteroidetes species were reduced following fecal stream diversion compared with rectal samples (median Shannon diversity index of 2.76 vs. 2.18, P<0.01). Similar abundance of Phyla Firmicutes, Actinobacteria, Fusobacteria, Verrucomicrobia, and Proteobacteria was observed. CONCLUSION: By analyzing the microbiome of sigmoid-derived neovaginas, we studied the effects of fecal diversion on the microbial composition of the healthy intestine. Most changes were observed in the phylum Bacteroidetes, indicating that these bacteria are likely part of the diet-dependent (butyrate-producing) colonic microbiome. Bacteria of other phyla are likely to be part of the diet-independent microbiome.