Increased diversity of Blautia species in patients with ulcerative colitis

Ulcerative colitis (UC) is characterized by pronounced dysbiosis of the gut microbiota, with previous studies implicating multiple bacterial taxa in disease pathogenesis. This study investigated the species-level diversity of Blautia in 24 UC patients and 15 healthy controls (HC) using 16S rRNA gene sequencing and MALDI-TOF mass spectrometry for species identification. Results demonstrated a marked 10.9-fold increase in Blautia abundance in UC patients (mean 44.6% vs. 5.26% in HC, p=0.0003), with four species - B. obeum, B. luti, B. faecis, and unidentified Blautia sp. (ID 375)-accounting for >80% of the genus. Notably, B. luti showed 100% prevalence in UC patients versus 79.2% in HC (p=0.0086). This Blautia expansion paradoxically correlated with reduced abundance of protective bacteria, including Faecalibacterium duncaniae, Anaerostipes hadrus, and Dorea longicatena, and was associated with increased disease severity. Although Blautia species are known butyrate producers with anti-inflammatory properties, their overabundance in UC represents functional dysbiosis, in which the microbiota attempts metabolic compensation but fails to effectively deliver short-chain fatty acids in the pathologically altered colonic environment. The concurrent depletion of mucus-layer-associated bacteria indicates compromised intestinal barrier integrity. These findings establish Blautia diversity as a potential marker of dysbiosis for UC severity, opening new diagnostic and therapeutic avenues for disease stratification and targeted interventions aimed at restoring eubiotic composition through selective bacterial modulation.