Characterization of the ileal microbiota in rejecting and nonrejecting recipients of small bowel transplants

Small bowel transplantation can be a life-preserving procedure for patients with irreversible intestinal failure. Allograft rejection remains a major source of morbidity and mortality and its accurate diagnosis and treatment are critical. In this study, we used pyrosequencing of 16S ribosomal RNA gene tags to compare the composition of the ileal microbiota present during nonrejection, prerejection and active rejection states in small bowel transplant patients. During episodes of rejection, the proportions of phylum Firmicutes (p < 0.001) and the order Lactobacillales (p < 0.01) were significantly decreased, while those of the phylum Proteobacteria, especially the family Enterobacteriaceae, were significantly increased (p < 0.005). Receiver-operating characteristic analysis revealed that relative proportions of several bacterial taxa in ileal effluents and especially Firmicutes, could be used to discriminate between nonrejection and active rejection. In conclusion, the findings obtained during this study suggest that small bowel transplant rejection is associated with changes in the microbial populations in ileal effluents and support microbiota profiling as a potential diagnostic biomarker of rejection. Future studies should investigate if the dysbiosis that we observed is a cause or a consequence of the rejection process. Analysis of the gut microbial community in the ileostomy output of small bowel transplant patients can discriminate between patients that are or are not rejecting their grafted intestines.