Psychological stress-induced reductions in α-defensin-5 levels result in microbiota dysbiosis in mice with depression, and α-defensin-5 supplementation attenuates the unbalanced gut microbiota and metabolites.262 Fecal α-defensin-5 concentrations have been significantly correlated with gut microbiota composition, including being positively correlated with the beneficial bacteria Ruminococcaceae, Allobaculum, Sutterella, and Akkermansia, but they have been negatively correlated with the harmful bacteria Erysipelotrichaceae. This evidence concerns the gene DEFA5 and major depressive disorder.