The Composition of Colonic Commensal Bacteria According to Anatomical Localization in Colorectal Cancer

Colorectal cancer （CRC） is a multistage disease resulting from complex factors, including genetic mutations, epigenetic changes, chronic inflammation, diet, and lifestyle. Recent accumulating evidence suggests that the gut microbiota is a new and important player in the development of CRC. Imbalance of the gut microbiota, especially dysregulated gut bacteria, contributes to colon cancer through mechanisms of inflammation, host defense modulations, oxidative stress, and alterations in bacterial-derived metabolism. Gut commensal bacteria are anatomically defined as four populations： luminal commensal bacteria, mucus-resident bacteria, epithelium-resident bacteria, and lymphoid tissue-resident commensal bacteria. The bacterial flora that are harbored in the gastrointestinal （GI） tract vary both longitudinally and cross-sectionally by different anatomical localization. It is notable that the translocation of colonic commensal bacteria is closely related to CRC progression. CRC-associated bacteria can serve as a noninvasive and accurate biomarker for CRC diagnosis. In this review, we summarize recent findings on the oncogenic roles of gut bacteria with different anatomical localization in CRC progression.

结直肠癌是由遗传突变、表观遗传改变、慢性炎症、饮食和生活方式等多因素引起的多阶段疾病。最新研究表明,肠道菌群是结直肠癌发展过程中的重要参与者。肠道菌群稳态的失调,可通过诱发炎症、调控宿主防御、氧化应激和改变细菌代谢产物等机制促进结直肠癌的发生发展。值得注意的是,肠道横、纵截面上不同解剖部位的驻留菌群有所不同。根据细菌在肠道中定植部位的不同,可将其划分为4种类型:肠腔共生菌、肠黏膜驻留菌、上皮驻留菌和淋巴组织驻留菌。由于结肠共生细菌的易位与结直肠癌的发展密切相关,结直肠癌相关细菌可有望成为用于结直肠癌诊断的非侵入且准确性高的新型生物标志物。本文旨在总结和概述肠道不同解剖部位中的肠道菌群在结直肠癌发生发展中的作用。