Understanding the intricate interactions between microbiota and host

Table 1 Interactions of the gut microbiota with other organs of the body

Gut-organ axis	Interactions	Important bacteria associated	Ref.
Gut-brain axis	Communication between CNS, ANS, and ENS. Significant role in neuroinflammation, and neuropsychiatric disorders and neurological diseases, interaction with neurotransmitters like serotonin, noradrenaline, norepinephrine dopamine, and GABA	Candida, Enterococcus, Escherichia, Lactobacillus, Bifidobacterium, etc.	[43,44]
Gut-heart axis	Significant role in development of coronary artery diseases, hypertension, cardiac fibrosis, atherosclerosis, etc.	Escherichia spp., Shigella, Streptococcus, Ruminococcus, Veillonella, etc., and a decline in the abundance of Prevotella, Faecalibacterium, Megamonas	[45,46]
Gut-lung axis	Onset and progression of tuberculosis, chronic obstructive pulmonary disease, cystic fibrosis, asthma, etc.	Decreased abundance of Eubacterium, Bacteroides, Bifidobacterium and Feacalibacterium, and abundance of propionate and butyrate producers like Facelibacterium, Eubacterium and Phascolarctobacterium	[47]
Gut-liver axis	Development of non-alcoholic liver disease, cirrhosis, and hepatocellular carcinoma	Bifidobacterium, Lactobacillus, Enterobacteriaceae, Clostridiales, Bacteroides, Prevotella	[48]
Gut-pancreas axis	Significant effects on insulin signaling and glucose and lipid metabolism, along with onset and progression of diabetes mellitus and inflammation of the pancreas
Gut-bone axis	Dysbiois may result in osteoporosis, and other osteodegenerative diseases		[49]
Gut-muscle axis	Development of sarcopenia and muscular atrophy		[50]
Gut-skin axis	Skin-related disorders such as psoriasis, alopecia, rosacea, acne and skin cancer may result due to dysbiosis	Bacteroides and Faecalibacterium, Clostridium, Escherichia	[51]
Gut-reproductive axis	Suggested role in spermatogenesis and development of PCOS, cervical and ovarian cancer and postmenopausal disorders	Escherichia, Clostridium and Citrobacter, an increased abundance of microbiota such as Phocaeicola vulgatus, Bacillota, Streptococcus and Escherichia/Shigella complex, and a decreased population of Akkermansiaa and Oscillospiraceae	[52]
Gut-kidney axis	Onset and progression of chronic kidney diseases, acute kidney injury, and diabeteic kidney disease	Increased occurrence of bacteria including Clostridium spp., Enterobacteria, Eggerthella spp., and a decreased occurrence of Prevotella, Bacteroides, and Roseburia
Gut-bladder axis	Recurring urinary tract infections and overactive bladder		[53]

CNS: Central nervous system; ANS: Autonomic nervous system; ENS: Enteric nervous system; GABA: Gamma-aminobutyric acid; PCOS: Polycystic ovarian syndrome.

Table 2 Studies on the therapeutic potential of gut microbiota in the treatment of various diseases

Microbiota-based intervention	Disease treated	Observations	Ref.
Bifidobacterium lactis and Lactobacillus rhamnosus	Colorectal cancer	Significant reduction in cancer proliferation and improved epithelial barrier function in patients under placebo-controlled trials	[135]
Lactobacillus reuteri	Gastric cancer	Human adenocarcinoma epithelial cells of the gastric tissue (AGS) treated with test strain showed reduced proliferation in dose-dependent manner	[136]
Lactobacillus casei and Lactobacillus paracasei	Cervical cancer	Upregulation of apoptotic genes such as BAX, caspase 3, caspase 8 and caspase 9, downregulation of BCl-2 gene observed in HeLa cells	[137]
Fecal microbiota transplantation	Clostridium difficile infection	Full primary or secondary response was achieved in 7 patients, with no serious after-effects contrary to metronidazole-treated control group	[138]
Faecal microbiota transplantation	Ulcerative colitis		[139]
Fecal microbiota transplant	Recurrent hepatic encephalopathy	Improved cognition and dysbiosis	[140]