The gut microbiome is increasingly believed to play key roles in the pathogenesis of several enteric, metabolic and psychiatric diseases.
This case-control study used 16S ribosomal rRNA gene sequencing of stool samples to find a discriminatory microbial pattern in individuals with major depressive disorder (MDD) (n=599) and bipolar disorder (BD) (n=217) compared to healthy controls (HCs) (n=217).
The relative abundance of altered bacterial operational taxonomic units (OTUs) was sought. Neither MDD or BD groups were medicated, although both groups were experiencing depressive episodes, therefore isolated microbes were reflecting the current pathophysiological state.
MDD was characterised by altered covarying OTUs assigned to the Bacteroidaceae family. The upregulation of Bacteroidaceae OTUs and one downregulated Enterobacteriaceae OTU suggests that these OTUs may play a cooperative role in the gut microbial environment of MDD. BD showed disturbed covarying OTUs belonging to Lachnospiraceae, Prevotellaceae and Ruminococcaceae families.
A signature of 26 OTUs were identified that could distinguish patients with MDD from those with BD or HCs, four of which correlated with disease severity. A confirmed gut microbial classifier with diagnostic and differential diagnostic potential was also identified which can distinguish MDD from BD.
Gut microbiota-based clinical diagnostic assay development is required for differential diagnosis of MDD and BD.