Vancomycin Efficacy in Response to Dysbiosis in Atypical Colitis

The goal of this clinical trial is to learn how oral vancomycin therapy may contribute in treating paediatric inflammatory bowel disease, particularly atypical ulcerative colitis and PSC-associated colitis. It will also give more information on how this treatment affects gut microbiota and metabolism. The main questions it aims to answer are: 1. Does oral vancomycin improve disease activity and lead to remission (based on symptoms, biomarkers, and endoscopy findings)? 2. How does oral vancomycin change gut metabolism? 3. Does different types of colitis respond differently to oral vancomycin? Researchers will compare children receiving oral vancomycin plus standard therapy to those receiving standard therapy alone. The gut metabolisim before and after oral vancmycin will also be compared, as well as to healthy controls and children with typical ulcerative colitis. Participants will: 1. Take oral vancomycin (if assigned) together with conventional treatment for at least 3 months and up to 12 months depending on response 2. Visit the clinic approximately every 3 months for checkups, tests, and monitoring 3. Provide blood, stool, and saliva samples to study disease activity and microbiota activity 4. Undergo clinical assessments such as symptom scoring, imaging, and possibly endoscopy 5. Complete questionnaires about quality of life 6. Be monitored for side effects and treatment response throughout the study period