Differential gut microbiota profiles among normal colorectal mucosa, adenomatous and hyperplastic polyps in healthy volunteers: ColoMAR-1 study.

271 Background: Increasing evidence indicates that the interaction between intestinal microbiota and host cells plays an important role in colorectal cancer oncogenesis through immune, inflammatory and/or metabolic alterations. However, there are no clear evidence in the very early adenoma-carcinoma sequence at which microbiota species influences future steps to colorectal carcinoma. This study aims do find a point in the adenoma-carcinoma sequence ad witch microbiota species suggest the risk of a future tumor to develop less invasive forms of early diagnosis. Methods: In this cross-sectional study, healthy volunteers above 45 years old were selected to participate. Exclusion criteria includes previous colonoscopy performed in the last 5 years. Stool sample were collected before a colonoscopy with biopsy. Samples of normal mucosa were systematically obtained, and all polyps found were removed. In fecal samples, microbiota species were identified using GoodGut test: Bacteroides fragilis, Subdoligranulm variabile, Ruminococcus, Roseburia, Coprococcus , eubacteria, Faecalibacterium prausnitzii and Gemella morbillorum . Number of genomic copies/μL were analyzed using the Wilcoxon test. Results: From February to June 2024, 29 healthy volunteers between 45 and 69 years were recruited. 62% were female. Adenomatous polyps or hyperplastic polyps were found in 9 volunteers. No case of colorectal cancer was found. For species S. variabile, Ruminococcus, Roseburia, Coprococcus and F. prausnitzii , higher counts were found in stool samples from volunteers with adenomatous or hyperplastic polyps than in those from volunteer with a normal colonoscopy, both in the total count and after correction for bacterial load (p<0.001). For B. fragilis , bacterial count was higher in samples from volunteers with adenomatous polyps, but not in the samples from people with hyperplastic polyps compared with those samples from volunteers with a normal colonoscopy. G. morbillorum counts were not related to any type of polyps. None of this counts met the laboratory-designated threshold related to colorectal cancer. Conclusions: The presence of B. fragilis could be related to the differential risk of malignancy of adenomatous compared to hyperplastic polyps. Bacterial count for each sample and specie. Bacteria specie* Normal mucosa Adenoma Hyperplastic B. fragilis 22.13 22.3 20.42 S.variable 6.06 7.29 7.53 Ruminococcus, Roseburia, Coprococcus 6.08 7.29 7.47 F. prausnitzii 4.7 6.28 7.09 G.morbillorum 20.91 20.54 20.84 *Number of genomic copies/μL.