Background. The microbiome has been implicated in the pathogenesis of major depressive disorder (MDD) and suicidal behavior. We studied gut and oral microbiomes with respect to suicide attempt status, diagnosis (MDD vs HV), depression severity, and sex.
Methods. Stool and saliva samples were obtained from well-characterized unmedicated patients with DSM5 MDD (n=24), and HV (stool n=11; saliva n=10) for quantification of gut and oral microbiomes. DNA was extracted and 16S rRNA sequences from V3-V4 (stool) and V1-V2 (saliva) were amplified. We assessed alpha and beta diversity and performed microbiota profiling for differential abundance using DESeq2.
Results. Gut and oral microbiome were compositionally distinct between 1) MDD vs HV, 2) suicide attempters (n=9) vs non-attempters (n=15), and 3) males vs females. Among participants with MDD and a history of suicide attempt, a differential abundance analysis in gut microbiome using DESeq2 found that only Ruminococcus bromii was more abundant, while 6 taxa including Prevotella and Coprococcus species were less abundant, than in those without suicide attempt history. In oral microbiome, 5 taxa were enriched in those with suicide attempt history, and all were species from Alloprevotella or Prevotella, while in non-attempters only Neisseria was enriched. No group differences were seen in alpha or beta diversity, except with respect to sex.
Limitations. Given the modest sample size and multiple testing, these results require replication.
Conclusions. This study links the microbiome with both MDD and suicide attempt status.
Future work should further investigate identified microbes of interest. Our findings are consistent with large-scale studies finding Coprococcus to be lower in depression. Longitudinal studies can help in determining causality and assessing microbiome stability over time.