Microbiota and the gut-liver axis: Bacterial translocation, inflammation and infection in cirrhosis

Table 1 Changes in intestinal microbiota and clinical consequence in cirrhosis

	Ref.	Implicated dysbiosis	Potential biological functions
Cirrhosis vs healthy people	Stool samples, Bajaj et al[5]	Overgrowth of (family):	There is a reduction in autochthonous taxa that can be disruptive given that they produce short-chain fatty acids that reduce colonic inflammation and nourish colonocytes improving the intestinal barrier
		Leuconostocaceae ↑
		Enterobacteriaceae ↑↑↑
		Fusobacteriaceae ↑
		Alcaligenaceae ↑
		Reduction of (family):
		Clostridium Incertae sedis XIV ↓↓↓
		Lachnospiraceae ↓
		Ruminococcaceae ↓
	Mucosal samples, Bajaj et al[5]	Overgrowth of (family - genus):	There was a significantly lower abundance of autochthonous genera (Clostridium Incertae Sedis XIV) and a higher abundance of potentially pathogenic ones (Enterococcus, Proteus, Clostridium) in cirrhotic patients compared with the mucosa of healthy controls
		Clostridiaceae - Clostridium ↑
		Enterococcaceae - Enterococcus ↑↑
		Enterobacteriaceae - Proteus ↑
		Reduction of (family - genus):
		Clostridium Incertae sedis XIV ↓↓
		Ruminococcaceae - Subdoligranulum ↓
		Lachnospiraceae ↓
Cirrhotics with vs without infection	Stool samples, Bajaj et al[18]	Overgrowth of (family):	There is an increase in abundance of pathogenic taxa, reduction in autochthonous taxa and higher endotoxemia compared to uninfected patients despite matching for MELD-score and medication confounders
		Enterobacteriaceae ↑
		Reduction of (family):
		Clostridium Incertae sedis XIV ↓↓
		Lachnospiraceae ↓↓
		Ruminococcaeae ↓↓
		Veillonellaceae ↓
Cirrhotics with vs without inflammation	Stool samples, Bajaj et al[18]	Overgrowth of (family):	This relative overgrowth of Enterobacteriaceae can result in endotoxemia due to increased production with worsening intestinal permeability, which has been associated with worsening disease severity and complications in cirrhosis. The lower abundance of butyrate producing genera (such as Roseburia and Ruminococcaceae) might represent a trophic injury to colonocytes
		Bacteroidaceae
		Enterobacteriaceae
		Reduction of (family):
		Clostridium Incertae sedis XIV
		Lachnospiraceae
		Ruminococcaeae
		Roseburia
Cirrhotics with vs without hepatic encephalopathy	Mucosal samples, Bajaj et al[23]	Overgrowth of (family - genus):	Firmicutes such as members of genera Veillonella, Megasphaera, Bifidobacterium, and Enterococcus were higher in HE whereas Roseburia was more abundant in the no-HE group
		Enterococcaceae - Enterococcus ↑
		Veillonellaceae - Megasphaera ↑
		Bifidobacteriaceae - Bifidobacterium ↑↑
		Veillonellaceae - Veillonella ↑
		Reduction of (family - genus):
		Lachnospiraceae - Roseburia ↓↓
Higher MELD score	Stool samples, Bajaj et al[18]	Overgrowth of (family):	With the increase in cirrhosis severity, there was a significant increase in potentially pathogenic and decrease in autochthonous taxa
		Staphylococcae
		Enterococceae
		Enterobacteriaceae
		Reduction of (family):
		Clostridium Incertae sedis XIV
		Lachnospiraceae
		Ruminococcaeae
		Rikenellaceae
Cirrhotics with vs without decompensated disease	Stool samples, Bajaj et al[18]	Overgrowth of (family):	With the increase in cirrhosis severity, there was a significant increase in potentially pathogenic and decrease in autochthonous taxa
		Enterobacteriaceae ↑
		Alcaligenaceae ↑
		Reduction of (family):
		Clostridium Incertae sedis XIV ↓
		Lachnospiraceae ↓
		Ruminococcaceae ↓
		Veillonellaceae ↓
Aetiology of cirrhosis
Alcoholic aetiology vs others	Stool samples, Bajaj et al[18]	Overgrowth of (family):	Alcoholic cirrhotics had a significantly higher abundance of Enterobacteriaceae and Halomonadaceae, lower Lachnospiraceae, Ruminococcaceae, and Clostridialies XIV, despite statistically similar MELD score and BMI compared to those without alcoholic etiology
		Enterobacteriaceae ↑
		Halomonadaeace ↑
		Reduction of (family):
		Clostridiales Incertae sedis XIV ↓
		Lachnospiraceae ↓
		Ruminococcaceae ↓
NASH aetiology vs others		Overgrowth of (family):	There is a higher abundance of Porphyromonadaceae, Bacterioidaceae, and lower Veillonellaceae in NASH patients than the non-NASH counterparts
		Bacteroidaceae ↑
		Porphyromonadaceae ↑
		Reduction of (family):
		Veillonellaceae ↓

Normalized relative abundance: ↑/↓: 1-2 fold of increase/reduction vs control; ↑↑/↓↓: 3-6 fold of increase/reduction vs control; ↑↑↑/ ↓↓↓ > 7 fold of increasereduction vs control. NASH: Nonalcoholic steatohepatitis; MELD score: Model for end-stage liver disease score; BMI: Body mass index.