SRP373991 PRJNA835259 Commensal Roseburia from cows attenuates gut dysbiosis-induced mastitis through inhibiting bacterial translocation by producing butyrate in mice The precise mechanism by which gut dysbiosis contributes to the pathogenesis of extraintestinal diseases and how commensal microbes mediate these processes remain unclear. Here, we showed that cows with mastitis had marked gut dysbiosis, characterized by the enrichment of opportunistic pathogenic Escherichia_Shigella and the depletion of commensal Roseburia. Fecal microbiota transplantation from donor cows with mastitis (M-FMT) to recipient mice significantly caused mastitis and changed the gut and mammary microbiota in mice. Notably, M-FMT facilitated the translocation of pathobiont from the gut into the mammary gland, and the depletion of Enterobacteriaceae alleviated M-FMT-induced mastitis in mice. In contrast, commensal Roseburia intestinalis improved M-FMT-induced mastitis and microbial dysbiosis in the gut and mammary gland and limited bacterial translocation by producing butyrate, which was associated with inflammatory signaling inhibition and barrier repair. Our research suggests that commensal Roseburia alleviates gut dysbiosis-induced mastitis but further studies in dairy cows and humans are needed.