The Dual Roles of Gut Microbiota in Biliary Atresia: Mechanisms, Biomarker Potential, and Therapeutic Implications

Biliary atresia (BA) is a progressive fibroinflammatory cholangiopathy of infancy that rapidly advances to cholestasis, fibrosis, cirrhosis, and liver failure if bile drainage is not restored early. Although Kasai hepatoportoenterostomy (KPE) remains the standard first–line operation, many children still develop recurrent cholangitis, persistent cholestasis, and progressive native liver injury. Increasing evidence indicates that the gut microbiota participates in this clinical course through the gut–liver axis. In BA, dysbiosis may weaken the intestinal barrier, increase translocation of microbe–associated molecular patterns (MAMPs), amplify innate and adaptive immune activation, disturb bile acid signaling, and promote fibrogenic and ferroptosis–related injury. In contrast, beneficial taxa and their metabolites may preserve epithelial integrity, support immune tolerance, maintain bile acid homeostasis, and constrain oxidative stress. This review summarizes current evidence on these contrasting harmful and protective effects, stage–specific microbiome signatures reported before and after KPE, and critically evaluates the present status of microbiota–based biomarkers and interventions. We emphasize that although several microbial signatures and therapeutic approaches are promising, they are not yet ready for routine clinical implementation and require prospective validation with standardized endpoints.