Table 1.

Studies on gut microbiome composition in depression.

Authors/Year Country	Study Design	Study Subjects	Biospecimen	Diagnosis/Severity of Depression Scales	Mean severity of depression at baseline	Microbiological Analysis	Total score of quality assessment (0–10)
Jiang et al. (15) China	Cross-sectional	n = 29 patients with depression [Active-Major Depressive Disorder, (A-MDD)] n = 17 patients during response to antidepressant treatment [Responded-Major Depressive Disorder (R-MDD)] n = 30 healthy controls Age: 18–40 years	1) Fecal samples 2) Blood samples (Serum tumor necrosis factor-a (TNF-a), interleukin-1b (IL)-1b, IL-6, and brain-derived neurotrophic factor (BDNF) levels	Diagnostic and Statistical Manual of Mental Disorders Fourth Edition (DSM IV), Hamilton’s Depression Scale (HAMDS), Montgomery–Asberg Depression Rating Scale (MADRS)	HAMDS: 29.8 MADRS: 27.4	16S rRNA genes (V1–V3 regions), PCR, Pyrosequencing. α-diversity, ß-diversity, bacterial taxonomic composition	7
Kelly et al. (16) Ireland	Cross-sectional	n = 34 patients with depression n = 33 healthy controls Mean age: 45.8	Fecal sample Salivary cortisol Plasma Tryptophan and kynurenine pathway metabolites Plasma levels of IL-6, IL-8, TNF-a, and CRP Lipopolysaccharide binding protein	Diagnostic and Statistical Manual of Mental Disorders (DSM IV)/Hamilton rating scale for Depression (HAMD 17)/Beck Depression Inventory	HAMD: 19.5 Beck Depression: 32.4	16S rRNA genes, illumina MiSeq platform. α-diversity, ß-diversity, bacterial taxonomic composition	6
Aizawa et al. (21) Japan	Cross-sectional	n = 43 patients with depression n = 57 healthy controls Mean age: 40 years	Fecal samples	Diagnostic and Statistical Manual of Mental Disorders, 4th ed. (DSM-IV), Hamilton depression rating scale	HAM-D: 16.9	16S rRNA genes, Reverse Transcription quantitative PCR, bacterial taxonomic composition	5
Lin et al. (17) China	Cross-sectional	n = 60 patients with depression n = 60 healthy controls Age: 20–85 years	Fecal samples	Diagnostic and Statistical Manual of Mental Disorders (DSM-IVTR), Hamilton depression rating scale (HAM-D) scale	HAM-D ≥23	16S rRNA genes (V3-V4), Illumina MiSeq platform. bacterial taxonomic composition	6
Naseribafrouei et al. (25) Norway	Partially blinded observational study	n = 37, patients with depression n = 18 healthy controls Mean age: 48 years	Fecal samples	ICD-10, Montgomery-Asberg Depression Rating Scale (MADRS)	MADRS: 26.3	16S rRNA genes, PCR, Illumina sequencing. α-diversity, ß-diversity, bacterial taxonomic composition	5
Chen et al. (20) China	Cross-sectional	n = 10 people with depression n = 10 healthy controls Age:18–65 years	Fecal samples	Diagnostic and Statistical Manual of Mental Disorders, 4th ed. (DSM-IV), Hamilton’s Depression Scale	HAMDS: 25.6	Protein, Liquid chromatography-tandem mass spectrometry	6
Liu et al. (23) China	Cross-sectional	n = 40 IBS-D patients n = 15 people with depression n = 25 comorbidity patients with both IBS and depression n = 20 healthy controls Age >18 years	Fecal samples	Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV)/Self-Rating Depression Scale (SDS)	SDS:60	16S rRNA genes (V1 to V3 region), PCR, Pyro sequencing. α-diversity, ß-diversity, Bacterial taxonomic composition	7
Zheng et al. (24) China	Cross-sectional	n = 58 patients with depression, n = 63 healthy controls; age >18 years	Fecal samples	DSM-IV-TR, Hamilton Depression Rating Scale	HDRS: 22.8	16S rRNA genes (V3-V5 regions), PCR, illumina sequencing. α-diversity, ß-diversity, bacterial taxonomic composition	7
Chen et al. (22) China	Cross-sectional	n = 24 people with depression, n = 24 healthy controls; age >18 years old (18–60)	Fecal samples	Diagnostic and Statistical Manual of Mental Disorders IV, Hamilton Depression Rating Scale (HDRS-17)	HDRS: 23.04	16S rRNA genes (V3–V5 regions), PCR, Pyro sequencing. α-diversity, ß-diversity, Bacterial taxonomic composition	6