Table 2.

Alterations of gut microbiota compositions associated with Parkinson’s disease.

Comparisona	Microbiota	Sample	Mechanism	Ref.
					PD patients vs Healthy control	Proteus sp.↑ Bilophila sp.↑and Roseburia sp.↑Lachnospiraceae↓Rikenellaceae↓ Peptostreptococcaceae↓Butyricicoccus sp. ↓	Stool	SCFA-producing families decrease	(Scheperjans et al., 2015)
PD patients vs Healthy control	Lactobacillus↓Prevotellaceae↓ Peptostreptococcus↓ Butyricicoccus spp.↓Proteus↑ Enterobacter spp.↑	Stool	Decreased Prevotellace lead to increased intestinal permeability, systemic exposure of bacterial endotoxins	(Sampson et al., 2016)
PD patients vs Healthy control	Firmicutes ↓ Prevotella ↑ Faecalibacterium ↓	Stool	SCFA-producing taxon decrease	(Heinzel et al., 2020)
PD patients vs Healthy control	Ralstonia↑Proteobacteria↑ Enteococcaceae↑Blautia, Coprococcus↓, Roseburia↓and Faecalibacterium↓	Stool	Pro-inflammatory cytokine producing bacteria increased, anti-inflammatory bacteria decreased	(Keshavarzian et al., 2015)
PD patients vs Healthy control	Helicobacter pylori↑	Stool	Helicobacter pylori is a triggering factor in PD pathogenesis	(Çamcı and Oğuz, 2016)
PD patients vs Healthy control	Bacteroides fragilis ↓ Bifidobacterium↓	Stool	Bacteroides fragilis were related with worsening of motivation/activeness and Bifidobacterium was associated to hallucinations/delusions	(Minato et al., 2017)
PD patients vs Healthy control	Porphyromonas↑Corynebacterium↑, Prevotella, ↑Porphyromonas, ↑ Ruminococcaceae ↓Lachnospiraceae↓ Lactobacillus ↑Bifidobacteria↑	Stool	Opportunistic pathogens were increased, SCFAs producing bacteria reduced, probiotics with carbohydrate-metabolizing increased	(Wallen et al., 2020)
PD patients vs Healthy control	Akkermansia↑ Catabacter ↑Akkermansiaceae↑Roseburia, ↓Faecalibacterium↓ Lachnospiraceae↓	Stool	Akkermansia can increase the permeability of intestine, lead to α-syn fibrils aggregate in intestine butyrate producing bacteria decrease	(Nishiwaki et al., 2020)
PD patients vs Healthy control	Christensenellaceae, ↑Desulfovibrionaceae↑Bifidobacterium↑Bilophila↑Akkermansia↑ Lachnospiraceae↓Roseburia↓, Faecalibacterium↓	Stool, serum	Carbohydrate fermentation reduced, low butyrate synthesis capacity proteolytic fermentation and deleterious amino acid metabolites production increased	(Cirstea et al., 2020)
PD patients vs Healthy control	Bacteroidetes ↓Prevotellaceae ↓Enterobacteriaceae↑	Stool	SCFAs may induce ENS alterations and dysmotility of gastrointestinal in PD	(Unger et al., 2016)
PD patients vs Healthy control	Lactobacillus casei shirota ↓staphylococci ↑	Stool	Lactobacillus casei shirota can improve the bowel movement by decreasing the number of staphylococci in PD patients	(Cassani et al., 2011)
PD patients vs Healthy control	Bacillus spp.↓	Stool	convert L-tyrosine to L-DOPA	(Surwase and Jadhav, 2011)
PD mice vs Healthy control	Proteobacteria↑ Turicibacterales↑Enterobacteriales↑ Firmicutes↓ Clostridiales↓	Stool	Fecal SCFAs concentration decrease, increase DA and 5-HT levels, reduce activation of microglia and astrocytes	(Sun et al., 2018)

^aA comparison of condition A vs condition B; ↑, increase in condition A related to condition B; ↓, decrease in condition A related to condition B.