Background: Colonic transformation is defined by phenotypic alterations in the ileum after total proctocolectomy. Changes in microbiota of the ileal pouch and the roles of these microbes in colonic transformation, however, have not been addressed. Methods: A total of 151 stool samples were collected from patients with ulcerative colitis patients and an ileostomy, those with an ileal pouch, and healthy control volunteers. Bacterial DNA was extracted from stool, and the diversity of complex bacteria was assessed by terminal restriction fragment length polymorphism (T-RFLP) analysis, a novel DNA-based approach that enables us to investigate the presence of nonculturable bacteria. To determine whether ileal pouch bacterial communities shift to a more colon-like distribution, the relative abundance of terminal restriction fragments that could be classified as "colonic," "ileal," or "common" was investigated. Results: Cluster analysis demonstrated that most of the ileostomy samples were categorized into Cluster I or II and that less than 10% of ileostomy samples were classified into Cluster IV. In contrast, more than 90% of control samples were grouped in Cluster IV. In further analyses, the median lifetimes of pouches in Clusters I, II, III, and IV were significantly different at 11, 56, 265, and 310 days, respectively. T-RFLP patterns of the ileal pouch were characterized by a time-dependent decrease in "ileal" and increase in a part of "colonic" fragments, which represented mainly nonculturable bacteria such as the Clostridium coccoides group. Conclusion: T-RFLP analysis demonstrated that a time-dependent shift to a "colon-like" bacterial community, including nonculturable bacteria, in the ileal pouch after total proctocolectomy.
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