Altered Fecal Microbiota Composition in Patients with Major Depressive Disorder.

Accumulating evidence from animal studies supports the hypothesis that gut microbiota play an important role in central nervous system function, namely through inflammation, and the HPA axis, and by affecting neurotransmission.
Human studies have demonstrated increased bacterial translocation in mood disorders such as depression.

METHODS:
- Age: 18–40 years
- 46 patients with depression= 29 with active MDD and 17 with responded MDD.
- 30 healthy controls (HCs)
- Exclusion criteria: hypertension; cardiovascular disease; diabetes mellitus; obesity; liver cirrhosis; fatty liver disease; irritable bowel syndrome; inflammatory bowel disease; drug or alcohol abuse in the last year; use of antibiotics, probiotics, prebiotics, or synbiotics in the month before collection of the fecal sample; and known active bacterial, fungal, or viral infections.

RESULTS:
- Bacterial diversity was significantly higher in the A-MDD group than that in HC group, as indicated by the Shannon index.
- This increased fecal bacterial diversity was not found in the responded-MDD (R-MDD) vs. the HC group.
- Bacteroidetes, Proteobacteria, and Actinobacteria strongly increased in level, whereas that of Firmicutes was significantly reduced in the A-MDD and R-MDD groups compared with the HC group.
- MDD groups had increased levels of Enterobacteriaceae and Alistipes but reduced levels of Faecalibacterium.
- Negative correlation was observed between Faecalibacterium and the severity of depressive symptoms.

CONCLUSIONS:
These findings enable a better understanding of changes in the fecal microbiota composition in such patients, showing:
- either a predominance of some potentially harmful bacterial groups or
- reduction in beneficial bacterial genera.