This Chinese study aimed to characterize the gut microbiota of patients with major depressive disorder (MDD): one group of patients with acute MDD (who scored high on a depression scale, indicating clinically significant depression), called ‘active-MDD’, and a second group of patients with a history of MDD who had responded to treatment (achieving a 50% reduction in depression scale scores after 4 weeks of treatment), called ‘responded-MDD’. Researchers compared fecal samples of these patients with those of healthy controls.

Despite great individual variability, there were some trends. Both MDD groups showed increased Bacteroidetes, Proteobacteria, and Actinobacteria, along with decreased Firmicutes, compared to the control group.

Researchers observed increased bacterial diversity in the fecal samples of active-MDD subjects, but not responded-MDD subjects, compared to controls. They also found a negative correlation between Faecalibacterium and the severity of depressive symptoms.

This study provides a ‘snapshot’ of the microbiota in depressed patients and does not address causality in humans. Further studies will elucidate whether the gut microbiota can be a biomarker for depression.

Jiang H, et al. (2015) Altered fecal microbiota composition in patients with major depressive disorder. Brain, Behavior, and Immunity doi:10.1016/j.bbi.2015.03.016