Alterations in the Gut Microbiome in Ankylosing Spondylitis and Their Correlation with Disease Activity

The microbiome significantly influences immune dysfunction and gut dysbiosis in patients with ankylosing spondylitis (AS). This study focuses on defining the distinct microbial characteristics within AS and biomarkers associated with disease activity. 44 patients with AS and 50 healthy controls (HC) were recruited. 16S rRNA sequencing was conducted to assess the microbiome of stool samples. The Ankylosing Spondylitis Disease Activity Score with C-reactive protein (ASDAS-CRP) was calculated for all AS patients; scores ≥ 2.1 indicated high disease activity, while < 2.1 indicated low disease activity. Similar alpha diversity profiles were maintained in both AS and HC cohorts, whereas significant differences were identified in beta diversity. The compositional prevalence of Proteobacteria, particularly Gammaproteobacteria, and Enterobacterales, including Escherichia spp., in the AS group was significantly increased. On the other hand, beneficial taxa, including Firmicutes, Clostridia, Clostridiales, Lachnospiraceae, Ruminococcaceae, and Faecalibacterium, were highly abundant in the HC group. Among patients with AS, alpha diversity decreased in the high disease activity group compared to the low disease activity group, while beta diversity did not differ significantly. Moreover, Coprobacter spp. abundance positively correlated with the Bath Ankylosing Spondylitis Disease Activity Index (p = 0.032) and the ASDAS-CRP (p = 0.023). Patients with AS exhibit distinct gut microbiota profiles, with increased Proteobacteria and decreased beneficial taxa such as Firmicutes. Greater disease activity is accompanied by reduced alpha diversity, while Coprobacter spp. abundance correlates with disease activity, suggesting its potential as a biomarker.