Effect of Intestinal Carriage of *Pilosibacter Rotomagensis* on Intestinal Inflammatory Activity

Crohn's disease is a chronic inflammatory condition that can affect the entire digestive tract. The terminal ileum is the segment most frequently involved, and approximately one-third of patients present with disease limited to the ileum. In such cases, surgical resection to remove all inflammatory lesions may be performed. This procedure prevents recurrence in about 50% of patients within five years of surgery. The post-operative setting offers a prime opportunity to study the early pathophysiological stages of Crohn's disease and the risk factors for recurrence. While smoking is a well-established risk factor for recurrence, the role of other factors-such as a fistulizing phenotype or a history of small-bowel resection-remains a subject of debate. Meanwhile, the role of the gut microbiota in this process remains largely unclear. Currently, the prevention of post-operative recurrence relies exclusively on smoking cessation and biologic therapies. However, the efficacy of these biologics-particularly anti-TNFα (Tumor Necrosis Factor alpha) agents-is reduced in patients who received prior treatment with these drugs before surgery. Notably, the proportion of such pre-treated patients has risen over the last two decades, reaching 50%. Consequently, there is a need to expand the range of strategies available to prevent post-operative recurrence. A better understanding of host-gut bacteria interactions could help prevent postoperative recurrence. To date, only \*Faecalibacterium prausnitzii\* and Adherent-Invasive \*Escherichia coli\* (AIEC) have been associated with a lower and higher risk of postoperative recurrence, respectively. However, a randomized controlled trial showed that antibiotic treatment aimed at eradicating AIEC was no more effective than a placebo in Crohn's disease. These trial results reinforce the value of a strategy based on identifying anti-inflammatory bacterial species that may play a protective role against postoperative recurrence. \*Pilosibacter rotomagensis\* is a bacterial species recently isolated from humans by the INSERM U1073 team; it may play a key role in intestinal physiology. This species is distinguished by its high capacity to produce short-chain fatty acids-particularly butyrate-and by anti-inflammatory properties observed in various \*in vitro\* cellular models. The hypothesis of this project is that carriage of \*Pilosibacter rotomagensis\* could play a protective role against postoperative recurrence in ileal Crohn's disease.

Inclusion Criteria: * Patient aged 18 years or older * Patient with a history of ileocecal resection for Crohn's disease. * Patient with isolated ileal Crohn's disease at the time of ileocecal resection surgery. Exclusion Criteria: * Refusal to participate in the study. * Presence of residual digestive lesions associated with Crohn's disease (e.g., colonic or perineal involvement) less than one month after ileocecal resection. * Use of antibiotics or non-steroidal anti-inflammatory drugs (NSAIDs) within the 28 days prior to stool collection. * Patients with cancer of the digestive tract. * Pregnant patients.