Background
Bowel polyps are areas of benign but excessive proliferation of epithelial cells in the colon. Left untreated it is estimated that approximately 5% will grow into malignant colorectal cancers. An increasing body of research has correlated different stool microbiota with both gut health and malignant bowel cancers. However, less is known about the microbiome directly at the gut mucosa and whether this contributes to bowel polyp development and ultimately colorectal cancers.
Aim
This study aims to identify bacteria that are differentially abundant in the gut mucosa from people with and without early-stage bowel polyps.
Methods
Colonoscopy patients were recruited from Royal North Shore Hospital (HREC 2019/ETH00301) for indications including rectal bleeding, FOBT positive stool test, scheduled surveillance. Patients with inflammatory bowel disease were excluded. DNA extracted from patient mucosal biopsies with (n = 107) or without (n = 133) polyps underwent short read sequencing of the V3-V4 region of the 16S rRNA gene. Bacterial diversity was compared between groups. Composition plots and MaAsLin multivariate differential abundance analysis was used to identify differences that distinguish the two groups, taking covariates including age, gender, indications for colonoscopy and BMI into account.
Results
There were no statistically significant differences in alpha or beta diversity between cases with and without polyps. However, composition plots showed that Proteobacteria showed increased relative abundance and Firmicutes decreased relative abundance in Polyp-Associated compared to Polyp-Free cases in the proximal mucosa. In particular, proximal cases showed increased relative abundance of bacteria such as Escherichia Shigella and decreased relative abundance of Bacteroides masilliensis. In distal mucosa, Fusobacteria and Bacteriodota showed increased relative abundance and Firmicutes and Proteobacteria decreased relative abundance in Polyp-Associated cases compared to Polyp-Free patients. Changes in the abundance of Blautia ASVs were commonly found in the distal colon.
Conclusions
These findings suggest that there are species of bacteria that show minor differences in abundance between patients with and without early-stage polyps in the bowel mucosa.