Possible association of Bifidobacterium and Lactobacillus in the gut microbiota of patients with major depressive disorder

- The patients had significantly lower Bifidobacterium counts than the controls.
- The patients had tended to have lower Lactobacillus counts than the controls.
- Bacterial counts below the optimal cut-off point confer MDD risk for both bacteria.
- Decreased counts of these bacteria were associated with irritable bowel syndrome.
- Fermented milk consumption was associated Bifidobacterium counts in the patients.

BackgroundBifidobacterium and Lactobacillus in the gut have been suggested to have a beneficial effect on stress response and depressive disorder. We examined whether these bacterial counts are reduced in patients with major depressive disorder (MDD) than in healthy controls.MethodBifidobacterium and Lactobacillus counts in fecal samples were estimated in 43 patients and 57 controls using bacterial rRNA-targeted reverse transcription-quantitative polymerase chain reactionResultsThe patients had significantly lower Bifidobacterium counts (P=0.012) and tended to have lower Lactobacillus counts (P=0.067) than the controls. Individuals whose bacterial counts below the optimal cut-off point (9.53 and 6.49 log10 cells/g for Bifidobacterium and Lactobacillus, respectively) were significantly more common in the patients than in the controls for both bacteria (Bifidobacterium: odds ratio 3.23, 95% confidence interval [CI] 1.38-7.54, P=0.010; Lactobacillus: 2.57, 95% CI 1.14-5.78, P=0.027). Using the same cut-off points, we observed an association between the bacterial counts and Irritable bowel syndrome. Frequency of fermented milk consumption was associated with higher Bifidobacterium counts in the patients.LimitationsThe findings should be interpreted with caution since effects of gender and diet were not fully taken into account in the analysis.ConclusionOur results provide direct evidence, for the first time, that individuals with lower Bifidobacterium and/or Lactobacillus counts are more common in patients with MDD compared to controls. Our findings provide new insight into the pathophysiology of MDD and will enhance future research on the use of pro- and prebiotics in the treatment of MDD.