Table 1.

Summary of bacteria that are directly related to the progression of Non-Alcoholic Fatty Liver Disease (NAFLD).

Bacteria Species	Characteristics	Main Effects	Experimental Models	Refs.
Faecalibacterium prausnitzii	Firmicutes phylum. Butyrate-producing bacteria. >5% of the total gut microbiota in healthy humans.	↓ [F. prausnitzii] → >5% fat hepatic content and ↑ adipose tissue inflammation in humans. ↑ [F. prausnitzii] → Lower lipid content, ↓ ALT and ↓ AST, ↑ CDKN1A (inversely correlated with NAFLD), ↓ hepatic fibrosis.	Clinical study with 31 participants with high hepatic fat content. HFD mice fed with F. prausnitzii vs. control mice and HFD mice not fed.	[74,75]
Bilophila wadsworthia	Gram-negativeBacteria. Proteobacteria phylum. Associated with diets rich in fat.	↑ [Bilophila wadsworthia] → ↑ Serum liver enzymes, hepatic steatosis and ↑ cholesterol levels. ↑ Hepatic lipid content and ↑ hepatic TG, ↓ butyrate metabolism pathway activation and ↑ SAA and IL-6. ↑ [Bilophila wadsworthia] → Stimulate systemic inflammation, intestinal barrier defect, bile acid dysmetabolism and interrupting tight junction integrity.	B. wadsworthia infection on specific pathogen-free mice. HFD mice fed with B. wadsworthia.	[76,77]
Helicobacter pylori	Gram-negative Bacteria. Proteobacteria phylum. Common infection in humans.	↑ [H. pylori] → -↑ Chronic inflammation and IR → ↑ TNF-α, IL-1β, IL-6 and IL-8. ↑ [H. pylori] → ↓adiponectin and leptin, ↑ fetuin-A → cytokines release ↑ [H. pylori] → ↑ Flora dysbiosis and mucosal permeability → ↑endotoxemia.	Clinical studies of NAFLD patients with H. pylori in a meta-analysis study.	[78,79,80]
Klebsiella pneumoniae	Gram-negative Bacteria. Proteobacteria phylum Endogenous alcohol-producing bacteria.	↑ [K. pneumoniae] → ↑ Endogenous OH → ↑ ROS, ↑ hepatic steatosis, ↑ TG, AST and AST. ↑ Immune cells and inflammation in liver ↑ Biosynthesis FAs and Fat storage	Clinical study with NAFLD and controls individuals colonized by K. pneumoniae. NAFLD mice induced by K. pneumoniae.	[81]
Akkermansia muciniphila	Gram-negative Bacteria Verrucomicrobia phylum 3–5% of the Gut microbiota Mucin-degrading activity.	↓ [A. muciniphila] → ↑ obesity, metabolic disorders, ↑ fat mass gain, ↑ body weight, ↑ inflammation, ↑ insulin resistance and ↑ glucose tolerance ↑ [A. muciniphila] → ↓ metabolic disorders, ↓ obesity, ↓ insulin sensitivity, ↓ fat mass and liver steatosis, ↓ [cholesterol] Regulation of mucus layer thickness → ↓ permeability → ↓ Endotoxemia	A. muciniphila in HFD-induced obese mice A. muciniphila supplementation in specific pathogen-free-grade mice.	[82,83]