XDH and major depressive disorder: Treatment with the strains CCFM1229 and CCFM1228 reduced anxiety- and depression-related behaviours in a chronic stress depression model, possibly by increasing the relative abundance of bacterial genera such as Anaerotruncus, Lachnospiraceae UCG-001, Ruminococcaceae UCG-005, Rikenellaceae RC9 gut group, and Bifidobacterium to regulate xanthine oxidase activity in the brain.