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Biliary atresia is progressive fibro-inflammatory cholangiopathy of young children. Central to pathogenic mechanisms of injury is the tissue targeting by the innate and adaptive immune cells. Among these cells, neutrophils and the IL-8/Cxcl-8 signaling via its Cxcr2 receptor have been linked to bile duct injury. Here, we aimed to investigate whether the intestinal microbiome modulates Cxcr2-dependent bile duct injury and obstruction. Adult wild-type (WT) and Cxcr2-/- mice were fed a diet supplemented with sulfamethoxazole/trimethoprim (SMZ/TMP) during pregnancy and lactation, and their pups were injected intraperitoneally with rhesus rotavirus (RRV) within 24 hours of life to induce experimental biliary atresia. The maternal exposure to SMZ/TMP significantly lowered the incidence of jaundice and bile duct obstruction and resulted in improved survival, especially in Cxcr2-/- mice. Analyses of the microbiome by deep sequencing of 16S rRNA of the neonatal colon showed a delay in bacterial colonization of WT mice induced by SMZ/TMP, with a notable switch from Proteobacteria to Firmicutes. Interestingly, the genetic inactivation of Cxcr2 alone produced a similar bacterial shift. When treated with SMZ/TMP, Cxcr2-/- mice infected with RRV to induce experimental biliary atresia showed further enrichment of Corynebacterium, Anaerococcus and Streptococcus. Among these, Anaerococcus lactolyticus was significantly associated with a suppression of biliary injury, cholestasis, and survivability. These results suggest that the postnatal development of the intestinal microbiota is an important susceptibility factor for experimental biliary atresia.