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Objective Accumulating evidence from microbial studies have highlighted the modulatory roles of intestinal microbes in numerous human diseases, however, the shared microbial signatures across different diseases remain relatively unclear. Methods To consolidate existing knowledge across multiple studies, we performed meta-analyses of 17 disease types, covering 34 case–control datasets of 16S rRNA sequencing data, to identify shared alterations among different diseases. Furthermore, the impact of a microbial species, Lactobacillus salivarius , was established in a dextran sodium sulphate–induced colitis model and a collagen type II–induced arthritis mouse model. Results Microbial alterations among autoimmune diseases were substantially more consistent compared with that of other diseases (cancer, metabolic disease and nervous system disease), with microbial signatures exhibiting notable discriminative power for disease prediction. Autoimmune diseases were characterized by the enrichment of Enterococcus , Veillonella , Streptococcus and Lactobacillus and the depletion of Ruminococcus , Gemmiger , Oscillibacter , Faecalibacterium , Lachnospiracea incertae sedis , Anaerostipes , Coprococcus , Alistipes , Roseburia , Bilophila , Barnesiella , Dorea , Ruminococcus2 , Butyricicoccus , Phascolarctobacterium , Parabacteroides and Odoribacter , among others. Functional investigation of L. salivarius , whose genus was commonly enriched in numerous autoimmune diseases, demonstrated protective roles in two separate inflammatory mouse models. Conclusion Our study highlights a strong link between autoimmune diseases and the gut microbiota, with notably consistent microbial alterations compared with that of other diseases, indicating that therapeutic strategies that target the gut microbiome may be transferable across different autoimmune diseases. Functional validation of L. salivarius highlighted that bacterial genera associated with disease may not always be antagonistic, but may represent protective or adaptive responses to disease. [ABSTRACT FROM AUTHOR]

Objectives: Spondyloarthritis (SpA) results from the interplay between genetic and environmental factors. An emerging modifiable factor is the human intestinal microbiota, which multiple studies in children and adults have shown to be abnormal in SpA patients, including enthesitis related arthritis and ankylosing spondylitis (AS). However, HLA-B27 itself appears to impact the contents of the microbiota and is more common in SpA patients versus controls, thus serving as a confounding factor in most comparative studies., Methods: This was a cross-sectional study that evaluated the contents of the faecal microbiota among 29 patients with HLA-B27+ AS and 43 healthy adults who underwent 16S sequencing and genotyping as part of the TwinsUK Programme., Results: HLA-B27 positive+ patients and healthy controls demonstrated substantial clustering based upon diagnosis. Decreased richness was observed among the AS patients, although measures of evenness were similar. After correction for multiple comparisons, several taxa - including Faecalibacterium prausnitzii and Coprococcus - were elevated in AS patients compared to controls, even when restricted to female subjects, while Bacteroides fragilis, Ruminococcus, and Akkermansia muciniphila were depleted in AS patients., Conclusions: Consistent with some previous studies, our study demonstrates in patients with AS associations with Coprococcus, Bacteroides, and Ruminococcus. Other findings, including increased Faecalibacterium, are inconsistent with previous studies and thus potentially underscore the necessity of evaluating HLA-B27 positive controls in studies evaluating the impact of the intestinal microbiota on SpA.