[Changes of intestinal microflora in patients with colorectal benign and malignant tumors in high altitude area and comparison with the normal population in low altitude area].

Objective: To analyze the changes of intestinal flora in patients with benign and malignant colorectal tumors in high altitude areas and to compare them with the normal population in low altitude areas.

Methods: The clinical data of 61 patients who underwent colonoscopy in the People' s Hospital of Tibet Autonomous Region from 2020 to 2022 were collected as the high altitude group. According to the colonoscopy results, they were divided into control group (29 cases), non-adenomatous polyp group (12 cases), adenoma group (10 cases), colorectal cancer group (10 cases). 17 patients who had negative colonoscopy results in the Peking University Third Hospital during the same period were collected as the low altitude control group. Before bowel preparation for colonoscopy, the fecal samples were collected. Then the DNA of bacteria in the fecal samples was extracted. The V3-V4 variable region of the 16S rRNA gene was PCR amplified and high-throughput sequenced. The species diversity of fecal flora was analyzed.

Results: Alpha diversity analysis showed that the species diversity of samples from the high altitude colorectal cancer group differed statistically from that of the high altitude non-adenomatous polyp group and the low altitude control group, and the species diversity of colorectal samples from the high altitude colorectal cancer group was higher than that of the other two groups. While beta diversity showed no significant difference among the five groups. Differences were found in phylum level analysis that the abundance of Actinobacteriota in the low altitude control group was significantly lower than those in each group of the high altitude area, while the abundance of Actinobacteriota in the colorectal cancer group was significantly lower than those in the other 3 groups of the high altitude area. Differences were found in genus level analysis that the abundance of Bacteroides, Phascclarctobacterium and Lachnoclostridium in the low altitude control group was significantly higher than those of all the groups in the high altitude area; the abundance of Blautia and Collinsella in the high altitude control group was the highest. Lactobacillus was not detected in the low altitude control group, while there was a highly significant difference (P < 0.05) in the level of Lactobacillus in the four groups of high altitude area, and the abundance of Lactobacillus was significantly higher in the control group than those of the other three groups. In the four groups of samples at high altitude, the abundance of Bifidobacterium decreased significantly, while the abundance of Christensenellaceae_R-7_group increased significantly.

Conclusion: Compared with the high and low altitude controls, the diversity and abundance of intestinal flora in patients with colorectal benign and malignant tumors at high altitudes are different. And the abundance of species are also diffe-rent at the phylum and genus levels, suggesting that altitude factors may have some influence on intestinal flora.