Analysis of the Intestinal Lumen Microbiota in an Animal Model of Colorectal Cancer

Abstract

Recent reports have suggested that multiple factors such as host genetics, environment and diet can promote the progression of healthy mucosa towards sporadic colorectal carcinoma. Accumulating evidence has additionally associated intestinal bacteria with disease initiation and progression. In order to examine and analyze the composition of gut microbiota in the absence of confounding influences, we have established an animal model of 1, 2-dimethylhydrazine (DMH)-induced colon cancer. Using this model, we have performed pyrosequencing of the V3 region of the 16S rRNA genes in this study to determine the diversity and breadth of the intestinal microbial species. Our findings indicate that the microbial composition of the intestinal lumen differs significantly between control and tumor groups. The abundance of Firmicutes was elevated whereas the abundance of Bacteroidetes and Spirochetes was reduced in the lumen of CRC rats. Fusobacteria was not detected in any of the healthy rats and there was no significant difference in observed Proteobacteria species when comparing the bacterial communities between our two groups. Interestingly, the abundance of Proteobacteria was higher in CRC rats. At the genus level, Bacteroides exhibited a relatively higher abundance in CRC rats compared to controls (14.92% vs. 9.22%, p<0.001). Meanwhile, Prevotella (55.22% vs. 26.19%), Lactobacillus (3.71% vs. 2.32%) and Treponema (3.04% vs. 2.43%), were found to be significantly more abundant in healthy rats than CRC rats (p<0.001, respectively). We also demonstrate a significant reduction of butyrate-producing bacteria such as Roseburia and Eubacterium in the gut microbiota of CRC rats. Furthermore, a significant increase in Desulfovibrio, Erysipelotrichaceae and Fusobacterium was also observed in the tumor group. A decrease in probiotic species such as Ruminococcus and Lactobacillus was likewise observed in the tumor group. Collectively, we can conclude that a significant difference in intestinal bacterial flora exists between healthy rats and CRC rats.

Role of colonic microbiota in colorectal carcinogenesis: A systematic review

“…Roseburia, which is a butyrate-producing genus, as well as Faecalibacterium, were also diminished in CRC patients (3.59% in healthy controls and 1.56% in CRC patients; p < 0.05); the same tendency was also seen in rats by Zhu et al (21)(22)(23).…”

“…Despite this, Eubacterium, a butyrate-producing genus of this family, was reduced in CRC rats, comparing with the control group (23).…”

“…This decrease in CRC patients (comparing with healthy controls) was also observed in animal studies with rats (2.32% vs. 3.71%; p < 0.001). Furthermore, Ruminococcus, another probiotic specie, was similarly decreased (23,26).…”

“…Also, Baxter et al, using transplanted faecal microbiota from both CRC patients and healthy individuals into germ-free mice, stated that Bacteroides where strongly correlated with increased tumor burden (p < 0.005). Finally, Zackular et al found an enrichment of members of the Bacteroides in tumour-bearing mice (p < 0.001) (23,28,29).…”

“…Fusobacterium, genus of this phylum, was shown to be more prevalent in colorectal cancer individuals than in healthy rats and humans (p = 0.001) (22,23). In addition, Kostic et al found Fusobacterium in 48% of adenomas and, in those patients, it was augmented in adenomatous tissue vs. surrounding tissue -p < 0.004 (24).…”