Role of Bile Acids and Microbiota in Clostridioides Difficile Infection in Ulcerative Colitis

For everyone : Inclusion Criteria: * Pediatric patients (\<18 years) consultant or hospitalized in the Gastroenterology department of Necker-Enfants Malades Hospital. * Information and consent of parents and the patient Exclusion Criteria: * Patient who received antibiotic or antifungal treatment in the 4 weeks prior to inclusion. * Patients colonized by C. difficile. * Pregnant or breastfeeding young girl. * Refusal of the protocol by parents or patient. For group 1: Patients with active UC Inclusion criteria: * Patient with UC, whatever the extent, except isolated proctitis (\<5 cm), diagnosed for more than 3 months according to the usual clinical, biological and endoscopic criteria. * UC in flare defined by a PUCAI score of between 35 and 65. Non-inclusion criteria: * Patient with IBD unclassified or Crohn's disease. * Patient with isolated proctitis (\<5 cm). * Colectomized patients. * Patients with sclerosing cholangitis associated with their UC or liver disease. Group 2: Patients in UC remission Inclusion criteria: * Patient with UC, whatever the extent, except isolated proctitis (\<5 cm), diagnosed for more than 3 months according to the usual clinical, biological and endoscopic criteria. * UC in remission defined by a PUCAI score \<10. Non-inclusion criteria: * Patient with IBD unclassified or Crohn's disease. * Patient with isolated proctitis (\<5 cm). * Colectomized patients. * Patients with sclerosing cholangitis associated with their UC or liver dise…