Comparison of serum microbiome composition in bipolar and major depressive disorders.

Bipolar disorder and major depressive disorder are debilitating psychiatric conditions which can be difficult to differentiate; however, recent studies have suggested that microbiome composition may be a potential tool in distinguishing between these two disorders. This study aimed to compare the serum microbiome composition of patients with bipolar disorder, major depressive disorder, and healthy controls. Serum samples were collected from 42 subjects with bipolar disorder, 30 with major depressive disorder, and 36 healthy controls. Bacterial DNA was isolated from bacteria-derived extracellular vesicles in the serum and then amplified and quantified with primers specific to the V3-V4 hypervariable region of the 16S rDNA gene. Sequence reads were clustered into operational taxonomic units and classified using the SILVA database. Alpha and beta diversity, individual taxa analysis based on phylum and genus, and functional pathways were compared. There was no statistical difference between alpha or beta diversity in patients with bipolar disorder and major depressive disorder; however, the Prevotella 2 and Ruminococcaceae UCG-002 genera were significantly more prevalent in patients with major depressive disorder than in either those with bipolar disorder or in healthy controls. Functional analysis of pathways revealed that the apoptosis function differed between all three groups. In conclusion, the Prevotella 2 and Ruminococcaceae UCG-002 genera were identified as potential candidates for distinguishing bipolar disorder and major depressive disorder. Further studies with larger sample sizes, longitudinal designs, and control for other various confounders are warranted.