Table 1.

Gut dysbiosis, its consequences, therapeutic interventions and their outcomes in various mental health disorders

Mental health disorder	Change in gut microbiota	Consequences of microbial dysbiosis	Therapeutic interventions	Observations after treatment/therapy	References
Autism spectrum disorder (ASD)	Alterations in  Bacteroidetes/firmicutes ratio Increase abundance of  Bacteroides, Barnesiella, Clostridium and Roseburia Decreased abundance of  Bifidobacterium, Coprococcus, Dialister, Faecalibacterium, Prevotella, and Streptococcus	Less production of butyrate and lactate; mucin degradation	FMT Changes in diet Antibiotics	Increased abundance of Bifidobacterium, Prevotella, and Desulfovibrio FMT associated changes in GI and ASD symptoms	[20, 25, 26]
Attention-deficit/hyperactivity disorder (ADHD)	Increase abundance of  Bifdobacterium  Neisseria	Predicted enhanced biosynthesis of cyclohexadienyl dehydratase—enzyme required for dopamine synthesis	Micronutrient supplementation	Decline in abundance of Bifdobacterium	[27, 28]
General anxiety disorder (GAD)	Increase abundance of  Fusobacterium, Ruminococcus and Escherichia- Shigella Decrease in  SCFAs-producing genera— Faecalibacterium, Eubacterium and Sutterealla	Immune activation Degradation of mucin	Non-probiotic (supplementary of the resistant dextrin)	Improvement in anxiety symptoms	[29, 30]
Depression	Abundance of  Prevotella, Klebsiella, Enterobacteriaceae and Alistipes Decrease in  Faecalibacterium, Coprococcus, Dialister, Ruminococcus species  Lachnospiraceae family  Lactobacillus and Bifidobacterium species	Butyrate production decline Increased intestinal inflammation	FMT—capsule administration	Reduction in the psychological distress	[31, 32]
Bipolar disorder (BD)	Increase in  Bacteroidetes, Actinobacteria, class Coriobacteria, Lachnospira, Enterobacteriaceae, Flavonifractor Decrease in  Firmicutes  Butyrate producing genera—Roseburia, Faecalibacterium and Coprococcus, Ruminococcaceae	Reduction in butyrate production Abnormal glucose metabolism Oxidative stress	Special nutritional diet Pharmacotherapies including lithium, anticonvulsants, and atypical antipsychotics (AAP)	Improvement in the symptoms of the disease	[32–36]
Schizophrenia (SCZ)	Increase in  Lactobacillus Streptococcus vestibularis, Lactobacillus fermentum, Enterococcus faecium, Alkaliphilus oremlandii, and Cronobacter sakazakii Cronobacter turicensis Decrease in  Veillonellaceae  Lachnospiraceae and Ruminococcaceae family, Proteobacteria,  Firmicutes, Clostridia, Haemophilus, Sutterella	Reduction in mucin, SCFAs Immune activation and neuroinflammation	Fiber rich diets suggested as an effective treatment FMT- capsule administration	Improved social-behaviors	[36–38]
Anorexia nervosa (AN)	Abundance in  Firmicutes, Methanobrevibacter smithii Reduction in  Bacteroides  Roseburia	Reduction in butyrate Production of autoantibodies leads to cross reactivity with host neuro-peptides and hormones Decrease in appetite and food efficiency	FMT (in GF-mice and AN patients)	Increase in Bacteroidetes Improvement in compulsive behavior	[39, 40]
Addiction (Substance abuse)	Abundance in  Bacteroidetes, Proteobacteria, Fusobacteria, Bacillaceae and Ruminococcaceae, Enterococcaceae and Staphylococcaceae  Paracoccus, Thauera, and Prevotella species	Neuroinflammation and gut inflammation	Antibiotic administration (in normal mice)	Enhanced sensitivity towards cocaine rewards	[42]
Post-traumatic stress disorder (PTSD)	Abundance in  Enterococcus and Escherichia-Shigella Decrease in  Actinobacteria, Lentisphaerae, and Verrucomicrobia, Lachnospiraceaeae and Ruminococcaceae	Decreased immunoregulation	FMT Diet change	Reduction in severity of PTSD	[43, 44]
Dementia	Increase in  Firmicutes/bacteroidetes ratio Decrease in  Bacteroidetes	Lower cognitive function	Probiotics	Alleviated cognitive dysfunction by modulating CNS functions	[47]
Alzheimer's disease (AD)	Abundance in  Escherichia and Shigella Reduction in  Eubacterium rectale	Production of proinflammatory cytokines Alteration in neurotransmitters level	Antibiotics	Use of antibiotics Reduced inflammation but sometime with side effects	[48]
Parkinson's disease (PD)	Abundance of  Bifidobacteriaceae, Lactobacillaceae, Pasteurellaceae, Christensenellaceae, Lachnospiraceae and Verrucomicrobiaceae Reduction in  Lachnospiraceae	Depletion in SCFA results in inflammation in brain and colon, constipation Mucin degradation	Drugs	Reduction in disease symptoms with side effects Improvement in the disease symptoms	[49, 50]