The primary objective of this case-control study aims to explore the role of bacterium Ruminococcus gnavus (R. gnavus) with intestinal biopsy and faecal sampling in the initiation and the development of spondyloarthritis (SPA) in comparison with health control subjets (patients without chronic disease but have indication to digestive endoscopy).

As secondary objectives, the study aims:

• to research the abundance of bacterial strain of R. gnavus in mucosal sampling by biopsy;
• to study the interaction between R. gnavus bacterium and mucus from histological sampling;
• to correlate the expression of genes of intestinal mucus with the variations of identified microbiota of mucus biopsy;
• to study the interaction between bacteria and intestinal epithelial cells during culture;
• to demonstrate perturbations of the immune responses by dysbiosis.

Inclusion Criteria:

Patients with SPA:

• Patients ⩾ 18 years;
• Diagnosed as spondyloarthritis (SpA) according ASAS classification;
• Affiliated to a social security scheme;
• Have signed the written informed consent form.

Control subjects:

• Subjects ⩾ 18 years;
• Subjects free of SPA and planned for a digestive endoscopy for another indication such as to explore the risk of colorectal cancer in family member;
• Affiliated to a social security scheme;
• Have signed the written informed consent form.

Exclusion Criteria:

• Subjects unable to understand the proposed study and/or sign a informed consent form;
• Pregnant women or breast feeding women;
• Subjects under guardianship or curatorship;
• Have taken antibiotic 1 month prior to inclusion;
• Presenting acute or chronic severe pathology may likely to interfere with the interpret of outcome;
• Refusal of subjects to participate to the study;
• Foreign patients under french AME scheme.