Table 4.

Human studies of the gut microbiota in T2D.

Reference	Authors	Year of Study	Subjects Number	Study Findings (Microbiota Changes in T2D vs. Control)
[89]	Li et al.	2020	20 T2D patients vs. 40 healthy individuals from North China	Decreased gut microbe diversity. T2D had reduced levels of Butyrate-producing bacteria (Bifidobacterium, Akkermansia, Faecalibacterium) and increased levels of bacteria involved in chronic inflammation (Dorea). Abundance in Dorea’s levels could identify patients at high risk for T2D.
[90]	Chávez-Carbajal et al.	2020	217 pre-diabetic and diabetic patients with and without treatment vs. healthy individuals (Mexican subjects)	Reduced bacterial richness and diversity. Pre-diabetic and diabetic groups had specific predicted metabolic characteristics and gut bacteria.
[91]	Doumatey et al.	2020	98 T2D Nigerians vs. 193 healthy Nigerians	Increased Actinobacteria and Bacteroidetes phyla. Decreased Firmicutes phylum. Clostridiaceae and Peptostreptococcaceaea families were significantly reduced.
[92]	Sedighi et al.	2017	18 T2D vs. 18 healthy	Bifidobacterium genus was reduced while Lactobacillus was significantly increased.
[93]	Inoue et al.	2017	12 T2D vs. 10 healthy (Japanese population)	11 pathways were significantly enriched in the diabetic group, including insulin signaling, glycolysis, and glycogenesis pathways. Significant reduction in Blautia genus, negatively correlated with HbA1c and glucose levels.
[94]	Wu et al.	2010	16 T2D vs. 12 healthy	Reduction in species profiles and reduced levels of Bifidobacterium genus and Bacteroides vulgatus.
[95]	Larsen et al.	2010	18 T2D vs. 18 healthy	Bacteroidetes: Firmicutes ratio and Bacteroides-Prevotella to Blautia coccoides -Eubacterium rectal correlated positively with plasma glucose levels.
[96]	Bilen et al.	2007	66 T2D vs. 50 healthy	Conjunctival flora from patients with T2D had increased Staphylococcus aureus and Staphylococcus epidermidis compared to control.