Objective To observe the effect of high - fat diet on the incidence of colorectal cancer( CRC)in an animal model,and to investigate the change of intestinal flora and the relationship with the occurrence of CRC. Methods From September 2014 to September 2015,120 SPF male Wistar rats which were four weeks old were randomly divided into four groups:normal diet + EDTA not induced tumor group(SDC group);normal diet + DMH induced tumor group(SDT group);high fat diet + EDTA not induced tumor group(HFDC group);high fat diet + DMH induced tumor group(HFDT group). Each group included 30 rats. SDC group and SDT group were fed with normal diet which contained 13. 5% fat while HFDC group and HFDT group were fed with high fat diet which contained 45. 0% fat. SDT group and HFDT group were intraperitoneal injected with DMH 40 mg/ kg every week for ten weeks,the SDC group and the HFDC group were intraperitoneal injected with 0. 9% sodium chloride with EDTA at the same amount. Rats′ whole period of colorectum was taken and stool samples were collected. Tissues of colorectum was examined by athologist. Genomic DNA was extracted using the QIAamp DNA Mini Kit according to the manufacturer′s instructions. Afterwards,the determination of genomic DNA,PCR amplification of 16S rRNA V3 region and the pyrosequencing and bioinformatic analysis were performed in order to compare the differences of intestinal flora structure under high - fat diet and normal diet and the correlation between intestinal flora structure and CRC. Results The average tumor numbers was higher in HFDT group than in SDT group〔(3. 0 ± 0. 4)and(2. 0 ± 0. 4),t = 2. 143,P = 0. 038〕. Moreover, the result of pyrosequencing showed that the differences of Shannon diversity index among four groups were significant( P <0. 05). The Shannon diversity index was higher in SDC group and SDT group than in HFDT group(P < 0. 05). In SDC group, 1 407 bacteriophyta and 134 581 genuses were detected;In SDT group,808 bacteriophyta and 128 582 genuses were detected;In HFDT group,896 bacteriophyta and 91 957 genuses were detected,and in HFDC group 1 519 bacteriophyta and 125 197 genuses were detected. According to the result of OTU classification analysis,relative abundance of firmicutes,actinobacteria, and spirochaetes in SDT group were lower than in SDC group,relative abundance of bacteroides and fusobacterium in SDT group were higher than in SDC group( P < 0. 05). The relative abundance of firmicutes in HFDT group was lower than in HFDC group,relative abundance of bacteriodetes,fusobacteria and proteobacteria in HFDT group were higher than in HFDC group(P< 0. 05). Relative abundance of actinobacteria in HFDT group was lower than in SDT group,relative abundance of fusobacteria in HFDT group was higher than in SDT group(P < 0. 05). Conclusion High - fat diet increases the risk of CRC for rats in this study. The structure of intestinal flora changes through taking high fat diet and the relative abundance of multiple potential pathogenic bacteria also increases,especially for fusobacteria. High - fat diet may cause intestinal flora disorder which plays a certain role in the occurrence and development of CRC.%目的：采用高脂饮食干预结直肠癌模型大鼠，观察其结直肠癌发生、发展及肠道菌群结构改变情况，分析高脂饮食引发肠道菌群结构改变与结直肠癌发生的相关性。方法2014年9月—2015年9月，选取4周龄 SPF 级雄性 Wistar 大鼠120只，按照随机数字表法分为4组：普通饮食+乙二胺四乙酸（EDTA）非诱导肿瘤组（SDC 组）、普通饮食+1，2-二甲基肼（DMH）诱导肿瘤组（SDT 组）、高脂饮食+ EDTA 非诱导肿瘤组（HFDC 组）、高脂饮食+ DMH 诱导肿瘤组（HFDT 组），每组30只。SDC 组和 SDT 组大鼠给予含13.5%脂肪的普通饲料，HFDC 组和 HFDT组大鼠给予含45.0%脂肪的高脂饲料。SDT 组和 HFDT 组大鼠给予40 mg/ kg DMH 腹腔注射，1次/周，连续注射10周；SDC 组和 HFDC 组大鼠给予等量的 EDTA +0.9%氯化钠溶液腹腔注射。获取大鼠整段结直肠，收集大鼠肠道粪便样本，病理学检查结直肠组织，利用 QIAamp DNA Mini Kit 试剂盒进行基因组 DNA 抽提，然后进行基因组 DNA 鉴定、聚合酶链式反应（PCR）扩增16S rRNA V3可变区，采用焦磷酸测序和生物信息学分析比较高脂饮食与普通饮食干预下肠道菌群结构的差异及其与结直肠癌发生的相关性。结果 HFDT 组平均结直肠癌数目多于 SDT 组〔（3.0±0.4）与（2.0±0.4），t =2.143，P =0.038〕。焦磷酸测序结果分析显示，4组大鼠 Shannon 多样性指数比较，差异有统计学意义（P <0.05）；其中 SDC 组、SDT 组大鼠 Shannon 多样性指数高于 HFDT 组（P <0.05）。SDC 组检测到1407个门、134581个属菌群；SDT 组检测到808个门、128582个属菌群；HFDC 组检测到1519个门、125197个属菌群；HFDT组检测到896个门、91957个属菌群。基于光转换单位（OTU）群落聚类分析结果显示，SDT 组厚壁菌门、放线菌门、螺旋体门相对丰度较 SDC 组降低，拟杆菌门、梭杆菌门相对丰度较 SDC 组升高（P <0.05）；HFDT 组厚壁菌门相对丰度较 HFDC 组降低，变形菌门、拟杆菌门、梭杆菌门相对丰度较 HFDC 组升高（P <0.05）；HFDT 组放线菌门相对丰度较 SDT 组降低，梭杆菌门相对丰度较 SDT 组升高（P <0.05）。结论高脂饮食干预下结直肠癌诱导大鼠发生肿瘤的数量多于普通饮食的结直肠癌诱导大鼠，高脂饮食能够引起肠道菌群结构改变，增加多种潜在性致病菌，特别是梭杆菌门，提示高脂饮食及其导致的肠道菌群结构改变在结直肠癌的发生、发展中有一定的促进作用。
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