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Abstract
Background: Ulcerative Colitis (UC) is a chronic inflammatory bowel disease characterized by gut microbiota dysbiosis. This study aims to provide a transparent and reproducible analysis by re-analyzing a publicly available raw 16S rRNA gene sequencing dataset to investigate the relationship between gut microbiota composition and disease activity in UC patients. Methods: We performed a complete re-analysis of a publicly available dataset (Papa et al., 2012) from the MicrobiomeHD database, which includes 16S rRNA gene sequencing data from stool samples of 43 UC patients and 24 healthy controls (HC). UC patients were stratified by clinical activity (inactive, n=11; mild, n=15; moderate, n=9; severe, n=8). All statistical analyses were performed from scratch, including calculating alpha diversity (Shannon index), phylum- and genus-level relative abundances, and Spearman correlations between microbial metrics and an ordinal disease activity score. Results: Our analysis confirmed a significant decrease in Shannon diversity in UC patients in remission (p=0.018) and with mild activity (p=0.002) compared to HCs. Shannon diversity showed a significant negative correlation with disease activity score (Spearman r = -0.294, p=0.016). Active UC patients exhibited a dramatic increase in Proteobacteria (22.6% vs. 0.99% in HC, p<0.0001). At the genus level, Ruminococcus was significantly depleted (p=0.006), while Klebsiella (p=0.003) and Haemophilus (p=0.003) were significantly enriched in active UC. Conclusion: This independent, fully reproducible analysis confirms that UC is characterized by reduced microbial diversity and a significant compositional shift, including depletion of beneficial bacteria and a marked bloom of pro- inflammatory Proteobacteria. These changes are directly correlated with disease activity.