The characteristics of gut microbiota in colorectal cancer with different microsatellite states.

The efficacy of immunotherapy varies between MSI-H and MSS colorectal cancer(CRC) patients. Multiple studies have shown that gut microbiota is closely related to CRC, but the causality of them has yet to be fully established.

This study aims to look for differential bacteria and related pathways by collecting feces from patients with different MS of CRC and healthy individuals, providing direction for immunotherapy of MSS CRC patients. 1. Explore the differences in gut microbiota between MSI-H and MSS CRC. 2.Provide new direction for the future clinical treatment of MSS CRC patients and improve their prognosis. From October 2021 to December 2025, fecal samples and medical records were collected from healthy individuals and patients with different genotypes of MSS and MSI-H CRC admitted to Shandong Cancer Hospital and Institute. 28 fecal samples were collected from MSI-H, MSS CRC patients and healthy individuals respectively. Then 84 fecal samples were analyzed using 16S rDNA sequencing.

Finally the differential microbial communities in the fecal samples of MSI-H and MSS CRC patients were analyzed based on the sequencing results, and healthy human fecal samples were used as controls to explore the role of differential microbial communities in CRC immunotherapy. The collected 84 fecal samples were subjected to 16s rDNA sequencing analysis. Through Venn plot analysis, it was found that there are 1774 same bacterial species in MSS and MSI-H CRC patients, 3951 unique bacterial species in MSS CRC patients, and 2571 unique bacterial species in MSI-H CRC patients. The species richness of intestinal microbiota in MSS was higher than that in MSI-H CRC patients.

Through species analysis, differential bacteria were identified among the samples submitted for testing, and further validation was obtained. Finally, based on the test results and comprehensive analysis of relevant literature, this study found that the bacteria with the most significant difference at phylum level between MSI-H and MSS CRC patients are Bacillota(p=0.024), Bacteroidota(p=0.024), Pseudomonadota(p=0.024), Actinomycetota(p=0.026), Verrucomicrobiota(p=0.037), and at genus level are Akkermansia(p=0.022), Alistipes(p=0.032), Anaerostipes(p=0.034), ASF356(p=0.016), Bacteroides(p=0.032), Bilophila(p=0.007), Coprococcus(p=0.037), Culicoidibacter(p=0.031), Enterocloster(p=0.049), Escherichia-Shigella(p=0.045), Faecalibacterium(0.042), Flavobacterium(p=0.037), Mediterraneibacter(p=0.037), Monoglobus(p=0.028), Oscillibacter(p=0.024), Parabacteroides(p=0.038), Ruthenibacterium(p=0.041), Streptococcus(p=0.015), Terrisporobacter(p=0.019), Tyzzerella(p=0.045), UCG-002(p=0.025), UCG-005(p=0.027), UCG-009(p=0.032), Veillonella(p=0.020). Among them, the relationship between Akkermansia, Faecalibactrium, Coprococcus and Bacteroides with immunotherapy is a hot research topic at home and abroad. There are differences in the species composition of gut microbiota between MSI-H and MSS CRC patients, which may provide new directions for further research.