Dangers of the chronic stress response in the context of the microbiota-gut-immune-brain axis and mental health: a narrative review.

More than 20% of American adults live with a mental disorder, many of whom are treatment resistant or continue to experience symptoms. Other approaches are needed to improve mental health care, including prevention. The role of the microbiome has emerged as a central tenet in mental and physical health and their interconnectedness (well-being). Under normal conditions, a healthy microbiome promotes homeostasis within the host by maintaining intestinal and brain barrier integrity, thereby facilitating host well-being. Owing to the multidirectional crosstalk between the microbiome and neuro-endocrine-immune systems, dysbiosis within the microbiome is a main driver of immune-mediated systemic and neural inflammation that can promote disease progression and is detrimental to well-being broadly and mental health in particular. In predisposed individuals, immune dysregulation can shift to autoimmunity, especially in the presence of physical or psychological triggers. The chronic stress response involves the immune system, which is intimately involved with the gut microbiome, particularly in the process of immune education. This interconnection forms the microbiota-gut-immune-brain axis and promotes mental health or disorders. In this brief review, we aim to highlight the relationships between stress, mental health, and the gut microbiome, along with the ways in which dysbiosis and a dysregulated immune system can shift to an autoimmune response with concomitant neuropsychological consequences in the context of the microbiota-gut-immune-brain axis. Finally, we aim to review evidenced-based prevention strategies and potential therapeutic targets.

Evolution and the critical role of the microbiota in the reduced mental and physical health associated with low socioeconomic status (SES).

The evolution of the gut-microbiota-brain axis in animals reveals that microbial inputs influence metabolism, the regulation of inflammation and the development of organs, including the brain. Inflammatory, neurodegenerative and psychiatric disorders are more prevalent in people of low socioeconomic status (SES). Many aspects of low SES reduce exposure to the microbial inputs on which we are in a state of evolved dependence, whereas the lifestyle of wealthy citizens maintains these exposures. This partially explains the health deficit of low SES, so focussing on our evolutionary history and on environmental and lifestyle factors that distort microbial exposures might help to mitigate that deficit. But the human microbiota is complex and we have poor understanding of its functions at the microbial and mechanistic levels, and in the brain. Perhaps its composition is more flexible than the microbiota of animals that have restricted habitats and less diverse diets? These uncertainties are discussed in relation to the encouraging but frustrating results of attempts to treat psychiatric disorders by modulating the microbiota.

Akkermansia muciniphila in neuropsychiatric disorders: friend or foe?

An accumulating body of evidence suggests that the bacterium Akkermansia muciniphila exhibits positive systemic effects on host health, mainly by improving immunological and metabolic functions, and it is therefore regarded as a promising potential probiotic. Recent clinical and preclinical studies have shown that A. muciniphila plays a vital role in a variety of neuropsychiatric disorders by influencing the host brain through the microbiota-gut-brain axis (MGBA). Numerous studies observed that A. muciniphila and its metabolic substances can effectively improve the symptoms of neuropsychiatric disorders by restoring the gut microbiota, reestablishing the integrity of the gut mucosal barrier, regulating host immunity, and modulating gut and neuroinflammation. However, A. muciniphila was also reported to participate in the development of neuropsychiatric disorders by aggravating inflammation and influencing mucus production. Therefore, the exact mechanism of action of A. muciniphila remains much controversial. This review summarizes the proposed roles and mechanisms of A. muciniphila in various neurological and psychiatric disorders such as depression, anxiety, Parkinson's disease, Alzheimer's disease, multiple sclerosis, strokes, and autism spectrum disorders, and provides insights into the potential therapeutic application of A. muciniphila for the treatment of these conditions.

Psychobiotic Lactobacillus plantarum JYLP-326 relieves anxiety, depression, and insomnia symptoms in test anxious college via modulating the gut microbiota and its metabolism.

Introduction: Test anxiety is a common issue among college students, which can affect their physical and psychological health. However, effective interventions or therapeutic strategies are still lacking. This study aims to evaluate the potential effects of Lactobacillus plantarum JYLP-326 on test anxious college students. Methods: Sixty anxious students were enrolled and randomly allocated to the placebo group and the probiotic group. Both groups were instructed to take placebo and JYLP-326 products twice per day for three weeks, respectively. Thirty unanxious students with no treatments were assigned to a regular control group. The anxiety, depression, and insomnia questionnaires were used to measure students' mental states at the baseline and the end of this study. 16S rRNA sequencing and untargeted metabolomics were performed to analyze the changes in the gut microbiota and fecal metabolism. Results: The questionnaire results suggested that JYLP-326 administration could relieve the symptoms of anxiety, depression, and insomnia in test anxious students. The gut microbiomes of the placebo group showed a significantly greater diversity index than the control group (p < 0.05). An increased abundance of Bacteroides and Roseburia at the genus level was observed in the placebo group, and the relative abundance of Prevotella and Bifidobacterium decreased. Whereas, JYLP-326 administration could partly restore the disturbed gut microbiota. Additionally, test anxiety was correlated with disordered fecal metabolomics such as a higher Ethyl sulfate and a lower Cyclohexylamine, which could be reversed after taking JYLP-326. Furthermore, the changed microbiota and fecal metabolites were significantly associated with anxiety-related symptoms. Conclusion: The results indicate that the intervention of L. plantarum JYLP-326 could be an effective strategy to alleviate anxiety, depression, and insomnia in test anxious college students. The potential mechanism underlying this effect could be related to the regulation of gut microbiota and fecal metabolites.

The Muscle-Gut-Brain Axis and Psychiatric Illness.

The microbiota-gut-brain axis (MGBA) has been the subject of much research over the past decade, offering an exciting new paradigm for the treatment of psychiatric disorders. In this review, the MGBA is extended to include skeletal muscle and the potential role of an expanded "muscle-gut-brain axis" (MuGBA) in conditions such as anxiety and depression is discussed. There is evidence, from both preclinical and human studies, of bidirectional links between the gut microbiome and skeletal muscle function and structure. The therapeutic role of exercise in reducing depressive and anxiety symptoms is widely recognised, and the potential role of the gut microbiota-skeletal muscle link is discussed within this context. Potential pathways of communication involved in the MuGBA including the tryptophan-kynurenine pathway, intestinal permeability, immune modulation, and bacterial metabolites such as short-chain-fatty-acids are explored.

The gut microbiome and mental health: advances in research and emerging priorities.

The gut microbiome exerts a considerable influence on human neurophysiology and mental health. Interactions between intestinal microbiology and host regulatory systems have now been implicated both in the development of psychiatric conditions and in the efficacy of many common therapies. With the growing acceptance of the role played by the gut microbiome in mental health outcomes, the focus of research is now beginning to shift from identifying relationships between intestinal microbiology and pathophysiology, and towards using this newfound insight to improve clinical outcomes. Here, we review recent advances in our understanding of gut microbiome-brain interactions, the mechanistic underpinnings of these relationships, and the ongoing challenge of distinguishing association and causation. We set out an overarching model of the evolution of microbiome-CNS interaction and examine how a growing knowledge of these complex systems can be used to determine disease susceptibility and reduce risk in a targeted manner.

Co-occurrence of gut microbiota dysbiosis and bile acid metabolism alteration is associated with psychological disorders in Crohn's disease.

This study aims to elucidate the relationships between gut microbiota, bile acid metabolism, and psychological comorbidity in Crohn's disease (CD). We profiled the fecal microbiota composition and quantified the bile acid pool of 39 CD patients and 14 healthy controls using 16S rRNA gene sequencing and liquid chromatography-tandem mass spectrometry, respectively. Significant reductions in the secondary bile acids, LCA and DCA, were found in both the feces and serum samples of CD patients, while the concentration of 7-DHCA was particularly higher in the serum of CD patients with psychological disorders. The fecal levels of HDCA and 12-DHCA of the CD patients were inversely correlated with their Self-Rated Depression Scale (SDS) scores, whereas the serum level of 7-DHCA was positively correlated with the SDS scores. In addition, the fecal levels of TDCA, TLCA, and TßMCA showed a positive correlation with the Self-Rated Anxiety Scale (SAS) scores. The fecal microbiota biodiversity was particularly declined in CD patients with psychological disorders. An enrichment of Ruminococcus gnavus in CD patients may cause psychological disorders by affecting the microbiota-gut-brain axis via its ability to degrade the gut barrier, regulate the tryptophan-kynurenine metabolism, and modulate bile acid metabolism. In addition, the overabundant Enterobacteriaceae and Lachnospiraceae in CD patients may contribute to psychological comorbidity via dysregulating their bile acids metabolism. Taken together, changes in the gut microbiota composition may cooperate with alterations in the bile acid metabolism that are involved in the development of psychological disorders in CD.

Gut microbiota and neuropsychiatric disorders: Implications for neuroendocrine-immune regulation.

Recently, increasing evidence has shown gut microbiota dysbiosis might be implicated in the physiological mechanisms of neuropsychiatric disorders. Altered microbial community composition, diversity and distribution traits have been reported in neuropsychiatric disorders. However, the exact pathways by which the intestinal microbiota contribute to neuropsychiatric disorders remain largely unknown. Given that the onset and progression of neuropsychiatric disorders are characterized with complicated alterations of neuroendocrine and immunology, both of which can be continually affected by gut microbiota via "microbiome-gut-brain axis". Thus, we assess the complicated crosstalk between neuroendocrine and immunological regulation might underlie the mechanisms of gut microbiota associated with neuropsychiatric disorders. In this review, we summarized clinical and preclinical evidence on the role of the gut microbiota in neuropsychiatry disorders, especially in mood disorders and neurodevelopmental disorders. This review may elaborate the potential mechanisms of gut microbiota implicating in neuroendocrine-immune regulation and provide a comprehensive understanding of physiological mechanisms for neuropsychiatric disorders.

Perturbations in Gut Microbiota Composition in Psychiatric Disorders: A Review and Meta-analysis.

Importance: Evidence of gut microbiota perturbations has accumulated for multiple psychiatric disorders, with microbiota signatures proposed as potential biomarkers. However, no attempts have been made to evaluate the specificity of these across the range of psychiatric conditions. Objective: To conduct an umbrella and updated meta-analysis of gut microbiota alterations in general adult psychiatric populations and perform a within- and between-diagnostic comparison. Data Sources: Cochrane Library, PubMed, PsycINFO, and Embase were searched up to February 2, 2021, for systematic reviews, meta-analyses, and original evidence. Study Selection: A total of 59 case-control studies evaluating diversity or abundance of gut microbes in adult populations with major depressive disorder, bipolar disorder, psychosis and schizophrenia, anorexia nervosa, anxiety, obsessive compulsive disorder, posttraumatic stress disorder, or attention-deficit/hyperactivity disorder were included. Data Extraction and Synthesis: Between-group comparisons of relative abundance of gut microbes and beta diversity indices were extracted and summarized qualitatively. Random-effects meta-analyses on standardized mean difference (SMD) were performed for alpha diversity indices. Main Outcomes and Measures: Alpha and beta diversity and relative abundance of gut microbes. Results: A total of 34 studies provided data and were included in alpha diversity meta-analyses (n = 1519 patients, n = 1429 control participants). Significant decrease in microbial richness in patients compared with control participants were found (observed species SMD = -0.26; 95% CI, -0.47 to -0.06; Chao1 SMD = -0.5; 95% CI, -0.79 to -0.21); however, this was consistently decreased only in bipolar disorder when individual diagnoses were examined. There was a small decrease in phylogenetic diversity (SMD = -0.24; 95% CI, -0.47 to -0.001) and no significant differences in Shannon and Simpson indices. Differences in beta diversity were consistently observed only for major depressive disorder and psychosis and schizophrenia. Regarding relative abundance, little evidence of disorder specificity was found. Instead, a transdiagnostic pattern of microbiota signatures was found. Depleted levels of Faecalibacterium and Coprococcus and enriched levels of Eggerthella were consistently shared between major depressive disorder, bipolar disorder, psychosis and schizophrenia, and anxiety, suggesting these disorders are characterized by a reduction of anti-inflammatory butyrate-producing bacteria, while pro-inflammatory genera are enriched. The confounding associations of region and medication were also evaluated. Conclusions and Relevance: This systematic review and meta-analysis found that gut microbiota perturbations were associated with a transdiagnostic pattern with a depletion of certain anti-inflammatory butyrate-producing bacteria and an enrichment of pro-inflammatory bacteria in patients with depression, bipolar disorder, schizophrenia, and anxiety.

Mitochondria and Antibiotics: For Good or for Evil?

The discovery and application of antibiotics in the common clinical practice has undeniably been one of the major medical advances in our times. Their use meant a drastic drop in infectious diseases-related mortality and contributed to prolonging human life expectancy worldwide. Nevertheless, antibiotics are considered by many a double-edged sword. Their extensive use in the past few years has given rise to a global problem: antibiotic resistance. This factor and the increasing evidence that a wide range of antibiotics can damage mammalian mitochondria, have driven a significant sector of the medical and scientific communities to advise against the use of antibiotics for purposes other to treating severe infections. Notwithstanding, a notorious number of recent studies support the use of these drugs to treat very diverse conditions, ranging from cancer to neurodegenerative or mitochondrial diseases. In this context, there is great controversy on whether the risks associated to antibiotics outweigh their promising beneficial features. The aim of this review is to provide insight in the topic, purpose for which the most relevant findings regarding antibiotic therapies have been discussed.

The role of microbiota-gut-brain axis in neuropsychiatric and neurological disorders.

Emerging evidence indicates that the gut microbiota play a crucial role in the bidirectional communication between the gut and the brain suggesting that the gut microbes may shape neural development, modulate neurotransmission and affect behavior, and thereby contribute to the pathogenesis and/or progression of many neurodevelopmental, neuropsychiatric, and neurological conditions. This review summarizes recent data on the role of microbiota-gut-brain axis in the pathophysiology of neuropsychiatric and neurological disorders including depression, anxiety, schizophrenia, autism spectrum disorders, Parkinson's disease, migraine, and epilepsy. Also, the involvement of microbiota in gut disorders co-existing with neuropsychiatric conditions is highlighted. We discuss data from both in vivo preclinical experiments and clinical reports including: (1) studies in germ-free animals, (2) studies exploring the gut microbiota composition in animal models of diseases or in humans, (3) studies evaluating the effects of probiotic, prebiotic or antibiotic treatment as well as (4) the effects of fecal microbiota transplantation.

Legionnaires' disease arising with hirsutism: case report of an extremely confusing event.

BACKGROUND: Legionella bacteria is a common cause of pneumonia, but the infection may affect several organs in the most serious cases. A systemic involvement ab initio could be non-specific, leading to a diagnostic misinterpretation. CASE PRESENTATION: A 33-year-old woman had been complaining of mental confusion, restlessness, aggressiveness, and, subsequently, hirsutism. After 3 weeks, the patient developed pneumonia and died during the hospitalization. The autopsy examination revealed a multi-organ necrotizing exudative disease involving the lung, the heart and the brain. The microbiological tests of tracheal aspirate were positive for Legionella pneumophila serotype 1. CONCLUSION: The Legionella infection may show a proteiform clinical course and an extra-pulmonary manifestation may be the first sign of the disease. Herein, we report a case of Legionella infection in a young female, presenting with non-specific neurological symptoms and hirsutism at onset, misdiagnosed as a metabolic disease.

Production of Psychoactive Metabolites by Gut Bacteria.

The gut microbiome plays a vital role in numerous aspects of physiology, including functions related to metabolism, the immune system, behaviour, brain structure and function. Furthermore, it is now becoming increasingly clear that alterations in microbial composition or diversity are implicated in several disease states, including anxiety, depression, autism spectrum disorder (ASD), Alzheimer's disease (AD), Parkinson's disease (PD), obesity, and diabetes. Therefore, therapeutic targeting of the gut microbiota has the potential to be useful in the treatment of both stress-related disorders and metabolic diseases. An important method by which the gut microbiome can influence the gut-brain axis is through microbial production of psychoactive metabolites. Several bacteria have been shown to produce metabolites which can impact host health, such as short-chain fatty acids, conjugated linoleic acid, antimicrobials, exopolysaccharides, and vitamins. Furthermore, several molecules with neuroactive functions, including serotonin, gamma-aminobutyric acid, catecholamines, and acetylcholine, have been isolated from bacteria within the human gut. This review aims to explore the psychoactive metabolites reported to be produced by gut bacteria, particularly those of relevance to stress-related disorders. Screening methods for psychoactive metabolite production, as well as the challenges and limitations of this research, will also be addressed. Finally, the implications of metabolite production for neuropsychiatric disorders such as depression, anxiety, and stress, behavioural disorders such as ASD, and neurodegenerative disorders such as AD and PD will be discussed.

Psychotropic Drugs and the Microbiome.

The human gut microbiome plays a key role in host physiology in health and disease. There is a growing emphasis on the bidirectional interaction between various medications and the gut microbiome. Here, we will first review how drugs can affect microbiome composition and how the microbiome can alter the pharmacodynamics and potentially pharmacokinetics of psychotropic medications. We will take into consideration different classes of psychotropics, including antipsychotics, antidepressants, antianxiety drugs, anticonvulsants/mood stabilisers, opioid analgesics, drugs of abuse, alcohol, nicotine, and xanthines. The varying effects of these widely used medications on microorganisms are becoming apparent from in vivo and in vitro studies. This has important implications for future drug discovery in psychiatry which will need to consider the host microbiome as a major potential target.

Sex-related patterns of the gut-microbiota-brain axis in the neuropsychiatric conditions.

Sex differences are often observed in psychiatric patients, especially major depressive disorders (MDD), schizophrenia, and developmental disorders, including autism spectrum disorders (ASDs). The prevalence rates between males and females seem variate according to the clinical condition. Although the findings are still incipient, it is suggested that these differences can involve neuroanatomical, neurochemical, and physiological sex differences. In this context, the microbiota-gut-brain axis hypothesis arises to explain some aspects of the complex pathophysiology of neuropsychiatric disorders. The microbiota composition is host-specific and can change conforming to age, sex, diet, medication, exercise, and others. The communication between the brain and the gut is bidirectional and may impact the entire system homeostasis. Many pathways appear to be involved, including neuroanatomic communication, neuroendocrine pathways, immune system, bacteria-derived metabolites, hormones, neurotransmitters, and neurotrophic factors. Although the clinical and preclinical studies are sparse and not very consistent, they suggest that sex differences in the gut microbiota may play an essential role in some neuropsychiatric conditions. Thus, this narrative review has as a mainly aim to show the points sex-related patterns associated to the gut-microbiota-brain axis in the MDD, ASDs, and schizophrenia.

Protocol for a systematic review on the role of the gut microbiome in paediatric neurological disorders.

INTRODUCTION: The gut-brain axis refers to the bidirectional communication that occurs between the intestinal tract and central nervous system (CNS). Through a series of neural, immune, endocrine, and metabolic signalling pathways, commensal microbiota are able to influence CNS development and neurological function. Alterations in gut microbiota have been implicated in various neuropathologies. The purpose of this review is to evaluate and summarise existing literature assessing the role of specific bacterial taxa on the development of neurodevelopmental, neuropsychiatric, and neurodegenerative pathologies of childhood. We will also discuss microbiota-based therapies dietary interventions and their efficacy. METHODS AND ANALYSIS: We will search PubMed, Cochrane Library, and OVID electronic databases for articles published between January 1980 and February 2021. A search method involving two rounds of reviewing the literature using a three-step method in each round will be performed. Two researchers will be selected, and screen titles and abstracts independently. The full text of selected articles will be assessed against inclusion criteria. Data will be extracted and evaluated using the appropriate Critical Appraisal Skills Programme (CASP) checklist. ETHICS AND DISSEMINATION: Findings from this study will be shared across relevant paediatric neurology and gastroenterology societies and submitted for peer review. This study did not require institutional ethics approval.

Gut microbiota alteration and modulation in psychiatric disorders: Current evidence on fecal microbiota transplantation.

The micro-organisms residing within the gastrointestinal tract, namely gut microbiota, form a dynamic population proper of each individual, mostly composed by bacteria which co-evolved symbiotically with human species. The advances of culture-independent techniques allowed the understanding of the multiple functions of the gut microbiota in human physiology and disease, the latter often recognising a predisposing condition in an imbalanced intestinal microbial ecosystem (dysbiosis). A complex mutual interconnection between the central nervous system (CNS), the intestine and the gut microbiota, known as "microbiota-gut-brain axis", has been hypothesized to play a pivotal role in maintaining central and peripheral functions, as well as mental health. Thus, dysbiosis with specific microbiota imbalances seems to be strongly associated with the onset psychiatric disorders by altering neurodevelopment, enhancing neurodegeneration, affecting behaviour and mood. Fecal microbiota transplantation (FMT) consists of transferring the fecal matter from a donor into the gastrointestinal tract of a recipient, and it is used to quickly modulate the gut microbiota. This review focuses on the uses of FMT in psychiatric disorders. FMT has been used to induce dysbiosis and to study the disease development, or to heal dysbiosis-related mental disorders. Overall, FMT of impaired microbiota resulted effective in enhancing psychiatric-like disturbances (mainly depression and anxiety) in recipient animals, plausibly by impairing immune system, inflammatory and metabolic pathways, neurochemical processes and neuro-transmission. On the other side, preclinical and clinical data suggest that reversing or mitigating dysbiosis seems a promising strategy to restore behavioural impairments or to obtain psychiatric symptom relief. However, current evidence is limited by the lack of procedural standardization, the paucity of human studies in the vastity of psychiatric conditions and the need of a microbiota-targeted donor-recipient matching.

Psychiatric Disabilities and Other Long-term Consequences of Childhood Bacterial Meningitis.

BACKGROUND: Bacterial meningitis is known to cause hearing impairments and neurologic deficits; however, less is known regarding psychiatric disabilities. In this study, we assessed psychiatric disabilities and other long-term consequences of childhood bacterial meningitis. METHODS: From a previously validated dataset, we selected children having had bacterial meningitis. We then reviewed medical records and child health records from discharge onwards to identify disabilities. We calculated the occurrence of disabilities with a 95% confidence interval (CI), and we used a χ test to assess possible individual risk factors associated with occurrence of disabilities. RESULTS: Of the 80 children included in this study, permanent disabilities not attributed to preexisting diseases were noted in 56% (CI: 45-67) during the mean observation period of 19 years and 2 months. Psychiatric disease was diagnosed in 30% (CI: 21-41), and another 5% (CI: 2-13) were under ongoing investigations for symptoms of psychiatric disease. Hearing impairments affected at least 30% (CI: 20-40), and neurologic deficits affected at least 23% (CI: 15-34). While other disabilities were often detected within the first year, psychiatric disabilities were detected after a mean time period of 14 years (CI: 11:1-16:11). Although some associations were noted, no individual risk factor was able to predict the occurrence of disabilities. CONCLUSIONS: Psychiatric disabilities affect more than one-third of survivors and are among the most common long-term consequence of childhood bacterial meningitis. Late discovery and predictive difficulties call for a revision of current guidelines to include a specific long-term strategy for detecting psychiatric disabilities.

A systematic review of microbiome changes and impact of probiotic supplementation in children and adolescents with neuropsychiatric disorders.

OBJECTIVES: In recent decades, the diagnostic and therapeutic implications of the microbiome changes and the impact of probiotic supplementation have increased rapidly. However, the potential for clinical translation of microbiome research for children and adolescents with psychiatric disorders is unclear. This review examined available evidence related to gut microbiota as well as the impact of probiotic supplementation on psychiatric disorders in the pediatric population reported to date. METHODS: We performed a literature search for the gut microbiota in child and adolescent population (0-18 years old) with mental health disorders from July 1999 through July 2019 in several databases: ClinicalTrials.gov, Ovid EBM Reviews, Ovid Embase, Ovid Medline, Ovid PsycINFO, Scopus, and Web of Science. RESULTS: A total of 7 studies met inclusion criteria consisting of randomized controlled trials and cohort studies that examined various associations between psychiatric disorders and gut microbiota in youth. Six studies examined the effects of various treatment interventions such as probiotic supplementation on microbiota composition and behaviors. One study showed an increase in prosocial behavior in children with Autism Spectrum Disorder (ASD) and an increase in the Lachnospiraceae family following prebiotic supplementation. Another study suggested that prebiotic supplementation increased bifidobacterial populations for ASD and healthy controls. A study evaluating infant supplementation of prebiotics showed both a decreased likelihood of developing Attention Deficit Hyperactivity Disorder (ADHD) or ASD and decreased gut Bifidobacterium. One study did not find significant differences in microbiome composition after micronutrient treatment. CONCLUSION: The main goal of this systematic review was to comprehensively examine and summarize the current evidence focused on the potential effect of the relationship between microbiota gut composition as well as the effects of probiotic supplementation on psychiatric disorders in children and adolescents. This is a relatively new area of research and the number of included studies is limited. More studies are needed to determine whether gut dysbiosis leads to the development and/or contributes to the severity of mental disorders or whether gut dysbiosis is a result of other processes that accompany mental disorders. CLINICAL SIGNIFICANCE: A better understanding of the specific bacteria contributions, gut-brain pathways, and role in pathophysiological mechanisms in neuropsychiatric disorders in the child and adolescent populations can possibly provide alternative tools for a clinical psychiatrist. Moreover, it may ultimately aid the clinician with intervention strategies, or detect populations at risk for developing neuropsychiatric disorders.