Table 2.

Changes in gut microbiota composition in various forms of cognitive impairment.

Phyla	Class	Order	Family	Genus	Species	Cognition			References
						MCI	D	AD
Firmicutes	Clostridia	Clostridiales						↓	[52]
			Clostridiaceae			↓		↓	[52]
				Clostridium				↓	[49]
		Eubacteriales	Ruminococcaceae					↓ ↓	[52] [49]
				Ruminococcus				↓	[52]
			Lachnospiraceae	- unclassified	Lachnospiraceae bacterium NK4A136	↓	↓ ↓	↓	[52] [51]
				Blautia		↓		↓ ↑	[52] [49]
			Eubacteriaceae	Eubacterium	E. rectale		↓ ↓	↑ ↑	[51] [50]
	Erysipelotrichia	Erysipelotrichales	Turicibacteraceae	Turicibacter				↓	[49]
	Negativicutes	Veillonellales	Veillonellaceae			↑			[52]
				Dialister				↓	[49]
		Selenomonadales	Acidaminococcaceae	Phascolarctobacterium				↑	[49]
	Bacilli	Lactibacillales	Lactobacillaceae	Lactobacillus			↑		[48]
		Staphylococcales	Gemellaceae	Gemella				↑	[49]
Bacteroidetes	Bacteroidia	Bacteroidales	Bacteroidaceae			↑ ↑			[52] [49]
				Bacteroides		↑ ↑	↓	↑ ↑ ↑	[47] [48] [49] [52]
					B. fragilis			↓	[50]
			Rikenellaceae	Alistipes				↑	[49]
Actinobacteria	Actinomycetia	Bifidobacteriales	Bifidobacteriaceae	Bifidobacterium			↑	↓	[47] [49]
	Coriobacteriia	Eggerthellales	Eggerthellaceae	Adlercreutzia				↓	[49]
Proteobacteria	Gammaproteobacteria	Enterobacteriales	Enterobacteriaceae					↑	[52]
				Escherichia/Shigella				↑	[50]
	Deltaproteobacteria	Desulfovibrionales	Desulfovibrionaceae	Bilophila				↑	[49]

Abbreviations: AD, Alzheimer’s Disease; D, dementia; MCI, Mild Cognitive Impairment.