Characterization of the human gut microbiome during travelers' diarrhea

Alterations in the gut microbiota are correlated with ailments such as obesity, inflammatory bowel disease, and diarrhea. Up to 60% of individuals traveling from industrialized to developing countries acquire a form of secretory diarrhea known as travelers'' diarrhea (TD), and enterotoxigenic Escherichia coli (ETEC) and norovirus (NoV) are the leading causative pathogens. Presumably, TD alters the gut microbiome, however the effect of TD on gut communities has not been studied. We report the first analysis of bacterial gut populations associated with TD. We examined and compared the gut microbiomes of individuals who developed TD associated with ETEC, NoV, or mixed pathogens, and TD with no pathogen identified, to healthy travelers. We observed a signature dysbiotic gut microbiome profile of high Firmicutes:Bacteroidetes ratios in the travelers who developed diarrhea, regardless of etiologic agent or presence of a pathogen. There was no significant difference in α-diversity among travelers. The bacterial composition of the microbiota of the healthy travelers was similar to the diarrheal groups, however the β-diversity of the healthy travelers was significantly different than any pathogen-associated TD group. Further comparison of the healthy traveler microbiota to those from healthy subjects who were part of the Human Microbiome Project also revealed a significantly higher Firmicutes:Bacteriodetes ratio in the healthy travelers and significantly different β-diversity. Thus, the composition of the gut microbiome in healthy, diarrhea-free travelers has characteristics of a dysbiotic gut, suggesting that these alterations could be associated with factors such as travel.     

Effect of gut microbial composition and diversity on major inhaled allergen sensitization and onset of allergic rhinitis

BackgroundDecreased gut microbiota diversity is associated with gut dysbiosis and causes various diseases, including allergic diseases. We investigated the relationship between gut microbial diversity and sensitization to major inhaled allergens. Furthermore, the relationship of allergic symptom onset with bacterial composition in sensitized individuals was investigated.MethodsThis study included 1092 local residents who had participated in the Iwaki Health Promotion Project in 2016. Blood samples were analyzed to ascertain specific IgE levels against major inhaled allergens (JCP, HD1, Grass-mix, Weed-mix). Nasal symptoms were estimated by questionnaires. Fecal samples were analyzed for bacterial 16S rRNA using next generation sequencing. The diversity index (α-diversity, β-diversity) and the composition of gut microbes in phylum/order levels were compared between patients sensitized or unsensitized to allergen, and symptomatic and asymptomatic groups.ResultsSome α-diversity metrics were significantly decreased in patients who were sensitized to any/all four allergens compared with the unsensitized group. β-diversity differed significantly between those unsensitized and sensitized to all allergens (aged 20–49 years), and between those unsensitized and sensitized to any/all four allergens (aged ≥50 years). The relative abundance of Bacteroidales was significantly lower in the unsensitized than in the sensitized group. The composition and diversity of gut microbiota were similar between the symptomatic and asymptomatic groups.ConclusionsOur results suggest that lack of diversity in gut microbiota has an effect on sensitization to allergens. Bacteroidales in order level may affect sensitization; however, the onset of allergy symptoms was not significantly associated with bacterial composition and diversity.     

Assessing gut microbiota perturbations during the early phase of infectious diarrhea in Vietnamese children

Diarrheal diseases remain the second most common cause of mortality in young children in developing countries. Efforts have been made to explore the impact of diarrhea on bacterial communities in the human gut, but a thorough understanding has been impeded by inadequate resolution in bacterial identification and the examination of only few etiological agents. Here, by profiling an extended region of the 16S rRNA gene in the fecal microbiome, we aimed to elucidate the nature of gut microbiome perturbations during the early phase of infectious diarrhea caused by various etiological agents in Vietnamese children. Fecal samples from 145 diarrheal cases with a confirmed infectious etiology before antimicrobial therapy and 54 control subjects were analyzed. We found that the diarrheal fecal microbiota could be robustly categorized into 4 microbial configurations that either generally resembled or were highly divergent from a healthy state. Factors such as age, nutritional status, breastfeeding, and the etiology of the infection were significantly associated with these microbial community structures. We observed a consistent elevation of Fusobacterium mortiferum, Escherichia, and oral microorganisms in all diarrheal fecal microbiome configurations, proposing similar mechanistic interactions, even in the absence of global dysbiosis. We additionally found that Bifidobacterium pseudocatenulatum was significantly depleted during dysenteric diarrhea regardless of the etiological agent, suggesting that further investigations into the use of this species as a dysentery-orientated probiotic therapy are warranted. Our findings contribute to the understanding of the complex influence of infectious diarrhea on gut microbiome and identify new opportunities for therapeutic interventions.     

Alternations of gut microbiota composition in neonates conceived by assisted reproductive technology and its relation to infant growth

ABSTRACT

The gut microbiome in newborns may be strongly influenced by their intrinsic host microenvironmental factors (e.g., the gestational age) and has been linked to their short-term growth and potentially future health. It is yet unclear whether early microbiota composition is significantly different in newborns conceived by assisted reproductive technology (ART) when compared with those who were conceived spontaneously. Additionally, little is known about the effect of gut microbiota composition on weight gain in early infancy. We aimed to characterize the features and the determinants of the gut microbiome in ART newborns and to assess the impact of early microbiota composition on their weight gain in early infancy in mother-infant dyads enrolled in the China National Birth Cohort (CNBC). Among 118 neonates born by ART and 91 neonates born following spontaneous conception, we observed significantly reduced gut microbiota α-diversity and declined Bacteroidetes relative abundance in ART neonates. The microbiota composition of ART neonates was largely driven by specific ART treatments, hinting the importance of fetus intrinsic host microenvironment on the early microbial colonization. Following up these neonates for six months after their births, we observed the effects of gut microbiome composition on infant rapid weight gaining. Collectively, we identified features and determinants of the gut microbiota composition in ART neonates, and provided evidence for the importance of microbiota composition in neonatal growth.     

The human gut mobile metagenome: a metazoan perspective

Using the culture independent TRACA system in conjunction with a comparative metagenomic approach, we have recently explored the pool of plasmids associated with the human gut mobile metagenome. This revealed that some plasmids or plasmid families are present in the gut microbiomes of geographically isolated human hosts with a broad global distribution (America, Japan and Europe), and are potentially unique to the human gut microbiome. Functions encoded by the most widely distributed plasmid (pTRACA22) were found to be enriched in the human gut microbiome when compared to microbial communities from other environments, and of particular interest was the increased prevalence of a putative RelBE toxin-antitoxin (TA) addiction module. Subsequent analysis revealed that this was most closely related to putative TA modules from gut associated bacteria belonging to the Firmicutes, but homologues of the RelE toxin were associated with all major bacterial divisions comprising the human gut microbiota. In this addendum, functions of the gut mobile metagenome are considered from the perspective of the human host, and within the context of the hologenome theory of human evolution. In doing so, our original analysis is also extended to include the gut metagenomes of a further 124 individuals comprising the METAHIT dataset. Differences in the incidence and relative abundance of pTRACA22 and associated TA modules between healthy individuals and those with inflammatory bowel diseases are explored, and potential functions of pTRACA22 type RelBE modules in the human gut microbiome are discussed.     

Prevalence of enteric pathogens among international travelers with diarrhea acquired in Kenya (Mombasa), India (Goa), or Jamaica (Montego Bay)

Stools from tourists from Europe and North America who acquired diarrhea in Mombasa (Kenya), Goa (India), or Montego Bay (Jamaica) were examined for enteric pathogens. Enterotoxigenic Escherichia coli (ETEC) was the most common pathogen (25%) identified in the 3 locations. Isolation of Shigella species was more frequent in Goa and Mombasa than in Montego Bay (10%, 9%, and 0.3%, respectively; P <.005). Viruses (rotaviruses and enteric adenoviruses) were found in 9% of travelers to the 3 areas. Of 275 ETEC isolates in this study, 158 (57%) produced a defined colonization factor antigen (CFA). Coli surface 6 (CS6) was the most frequent and was found in 41%-52% of CFA/CS-positive ETEC isolates. The frequency of resistance among bacterial enteropathogens to traditional antimicrobial agents was particularly high throughout the study period in all 3 regions. Quinolones were active against the bacterial enteropathogens in the 3 sites.     

Intestinal Dysbiosis: A Possible Mechanism of Alcohol-Induced Endotoxemia and Alcoholic Steatohepatitis in Rats

Background:  Clinical and animal data indicate that gut-derived endotoxin and other luminal bacterial products are necessary cofactors for development of alcoholic liver disease (ALD). Although gut leakiness is clearly an important cause of endotoxemia in ALD, it cannot fully explain endotoxemia in all ALD subjects and thus other factors may be involved. One possible factor is a change in gut microbiota composition (dysbiosis). Thus, the aim of our study was to interrogate the gut bacterial microbiota in alcohol-fed rats to see if chronic alcohol consumption affects gut bacteria composition.
Method:  Male Sprague–Dawley rats were given either alcohol or dextrose intragastrically by gavage twice daily for up to 10 weeks. A subgroup of rats was also given either a probiotic (lactobacillus GG) or a prebiotic (oats) by gavage. Ileal and colonic mucosal-attached microbiota composition were interrogated by Length Heterogeneity PCR (LH-PCR) fingerprinting.
Results:  Bacterial microbiota composition in alcohol-fed rats is not different from dextrose-fed rats at weeks 4 and 6. Mucosa-associated microbiota composition in the colon is altered at 10 weeks of daily alcohol gavage. Both LGG and oats prevented alcohol-induced dysbiosis up to 10 weeks of alcohol treatment.
Conclusion:  Daily alcohol consumption for 10 weeks alters colonic mucosa-associated bacterial microbiota composition in rats. Our data showed, for the first time, that daily alcohol consumption can affect colonic microbiome composition and suggest that dysbiosis may be an important mechanism of alcohol-induced endotoxemia. Further studies are needed to determine how dysbiotic microbiota contributes to development of ALD and whether therapeutic interventions targeted towards dysbiotic microbiota can prevent complications of alcoholism like ALD.     

Epidemiology, etiology and pathophysiology of traveler's diarrhea

Traveler's diarrhea (TD) is the most frequent health problem in travelers to developing countries. Several personal and environmental risk factors are at the basis of TD acquisition and are discussed in this paper. TD is caused by a wide range of infectious organisms, ETEC and EAEC bacteria strains being the main enteropathogens incriminated in TD. Other causative bacteria are: Shigella spp., Campylobacter spp., Vibrio spp., Aeromonas spp., Salmonella spp., and Plesiomonas spp. Parasite species are also included: Cyclospora cayetanensis, Giardia lamblia, Cryptosporidium, Entamoeba histolytica, as well as viruses: rotavirus, adenovirus, Norwalk virus. Due to the great diversity of pathogens incriminated, several pathophysiological mechanisms have been described and some of them are still poorly understood. The clinical symptoms present are also quite variable, although inflammatory and non-inflammatory diarrhea have been established as a classical and basic classification of diarrhea.     

Bacterial flora as a cause or treatment of chronic diarrhea

Intestinal microflora can be considered an organ of the body. It has several functions in the human gut, mostly metabolic and immunologic, and constantly interacts with the intestinal mucosa in a delicate equilibrium. Chronic diarrhea is associated with an alteration of gut microbiota when a pathogen invades the gut and also in several conditions associated with intestinal mucosal damage or bowel dysfunction, as in inflammatory bowel disease, irritable bowel syndrome, or small bowel bacterial overgrowth. This article discusses the basis of gut microbiota modulation. Evidence for the efficacy of gut microbiota modulation in chronic conditions is also discussed.     

Gut microbiota contributes to the distinction between two traditional Chinese medicine syndromes of ulcerative colitis

BACKGROUND Ulcerative colitis(UC)is considered to be closely associated with alteration of intestinal microorganisms.According to the traditional Chinese medicine(TCM)theory,UC can be divided into two disease syndromes called Pi-Xu-Shi-Yun(PXSY)and Da-Chang-Shi-Re(DCSR).The relationships among gut microbiota,TCM syndromes,and UC pathogenesis have not been well investigated.AIM To investigate the role of gut microbiota in UC and the distinction of microbiota dysbiosis between PXSY and DCSR syndromes.METHODS From May 2015 to February 2016,UC patients presenting to LongHua Hospital who met the established inclusion and exclusion criteria were enrolled in this retrospective study.Fresh stool specimens of UC patients with PXSY or DCSR were collected.The feces of the control group came from the health examination population of Longhua Hospital.The composition of gut bacterial communities in stool samples was determined by the pyrosequencing of 16S ribosomal RNA.The high-throughput sequencing reads were processed with QIIME,and biological functions were predicted using Phylogenetic Investigation of Communities by Reconstruction of Unobserved States.RESULTS The composition of gut bacterial communities in 93 stool samples(30 healthy controls,32 patients with PXSY syndrome,and 31 patients with DCSR syndrome)was determined by the pyrosequencing of 16S ribosomal RNA.Beta diversity showed that the composition of the microbiota was different among the three groups.At the family level,Porphyromonadaceae,Rikeneliaceae,and Lachnospiraceae significantly decreased while Enterococcus,Streptococcus,and other potential pathogens significantly increased in UC patients compared to healthy subjects.At the genus level,Parabacteroides,Dorea,and Ruminococcus decreased while Faeca-libacterium showed increased abundance in UC compared to healthy controls.Five differential taxa were identified between PXSY and DCSR syndromes.At the genus level,a significantly increased abundance of Streptococcus was observed in DCSR patients,while Lachnoclostridium increased in PXSY patients.The differential functional pathways of the gut microbiome between the PXSY and DCSR groups mainly included lipid metabolism,immunity,and the metabolism of polypeptides.CONCLUSION Our study suggests that the gut microbiota contributes to the distinction between the two TCM syndromes of UC.     

Relationships between gut microbiota,plasma glucose and gestational diabetes mellitus

Aims/IntroductionTo investigate the changes in the gut microbiome in the second trimester of pregnancy associated with later‐diagnosed gestational diabetes mellitus (GDM) and their relationship with fasting serum levels of metabolites, especially glucose.Materials and MethodsWe carried out a case–control study with 110 GDM patients and 220 healthy pregnant women who provided fecal samples for 16S ribosomal ribonucleic acid sequencing in the second trimester of pregnancy.ResultsOur results showed that GDM patients had lower α‐diversity that was significantly associated with glycemic traits. Principal coordinates analysis showed significantly different microbial communities, as within GDM patients, seven genera within the phylum Firmicutes and two within the phylum Actinobacteria were significantly decreased, and four genera within phylum Bacteroidetes were increased. In addition, microbiota co‐occurrence network analysis was carried out, and decreased genera within the phylum Firmicutes in GDM patients showed a significant negative correlation with oral glucose tolerance test values. Finally, microbial gene functions related to glycan biosynthesis and metabolism were found to be enriched in GDM patients.ConclusionsOur results show the relationship between changed gut microbiota composition in the second trimester of pregnancy before the diagnosis of GDM and fasting serum levels of metabolites, which might inform the diagnosis, prevention and treatment of GDM.     

A two-year study of bacterial, viral, and parasitic agents associated with diarrhea in rural Bangladesh

Enteric pathogens associated with diarrhea were studied for two years at a diarrhea treatment center in rural Bangladesh. Enterotoxigenic Escherichia coli (ETEC) was the most frequently identified pathogen for patients of all ages. Rotavirus and ETEC were isolated from approximately 50% and approximately 25%, respectively, of patients less than two years of age. A bacterial or viral pathogen was identified for 70% of these young children and for 56% of all patients with diarrhea. Most ETEC isolates were obtained in the hot dry months of March and April and the hot wet months of August and September. Rotavirus identification peaked in the cool dry months of December and January, but infected patients were found year-round. The low case-fatality rates for patients with watery diarrhea and substantial dehydration further document the usefulness of treating patients with diarrhea with either a glucose- or sucrose-base electrolyte solution such as those used in this treatment center.     

Altered gut microbial profile is associated with abnormal metabolism activity of Autism Spectrum Disorder

ABSTRACT

Autism Spectrum Disorder (ASD) is a severe neurodevelopmental disorder. To enhance the understanding of the gut microbiota structure in ASD children at different ages as well as the relationship between gut microbiota and fecal metabolites, we first used the 16S rRNA sequencing to evaluate the gut microbial population in a cohort of 143 children aged 2–13 years old. We found that the α-diversity of ASD group showed no significant change with age, while the TD group showed increased α-diversity with age, which indicates that the compositional development of the gut microbiota in ASD varies at different ages in ways that are not consistent with TD group. Recent studies have shown that chronic constipation is one of the most commonly obvious gastrointestinal (GI) symptoms along with ASD core symptoms. To further investigate the potential interaction effects between ASD and GI symptoms, the 30 C-ASD and their aged-matched TD were picked out to perform metagenomics analysis. We observed that C-ASD group displayed decreased diversity, depletion of species of Sutterella, Prevotella, and Bacteroides as well as dysregulation of associated metabolism activities, which may involve in the pathogenesis of C-ASD. Consistent with metagenomic analysis, liquid chromatography-mass spectrometry (LC/MS) revealed some of the differential metabolites between C-ASD and TD group were involved in the metabolic network of neurotransmitters including serotonin, dopamine, histidine, and GABA. Furthermore, we found these differences in metabolites were associated with altered abundance of specific bacteria. The study suggested possible future modalities for ASD intervention through targeting the specific bacteria associated with neurotransmitter metabolism.     

Alterations of the gut microbiome and metabolome in alcoholic liver disease

Alcohol consumption is one of the leading causes of liver diseases and liver-related death worldwide. The gut is a habitat for billions of microorganisms which promotes metabolism and digestion in their symbiotic relationship with the host. Alterations of gut microbiome by alcohol consumption are referred to bacterial overgrowth, release of bacteria-derived products, and/or changed microbiota equilibrium. Alcohol consumption also perturbs the function of gastrointestinal mucosa and elicits a pathophysiological condition. These adverse effects caused by alcohol may ultimately result in a broad change of gastrointestinal luminal metabolites such as bile acids, short chain fatty acids, and branched chain amino acids. Gut microbiota alterations, metabolic changes produced in a dysbiotic intestinal environment, and the host factors are all critical contributors to the development and progression of alcoholic liver disease. This review summarizes recent findings of how alcohol-induced alterations of gut microbiota and metabolome, and discusses the mecha-nistic link between gastrointestinal dyshomeostasis and alcoholic liver injury.     

Seasonal variation in etiology of travelers' diarrhea. Finnish-Moroccan Study Group.

The etiology of travelers' diarrhea was studied in 579 adult Finnish tourists participating in two packaged tours to Morocco in the winter (n = 233) and fall (n = 346) of 1989. A research team accompanied the travelers, and a laboratory for enteric pathogens was established in Agadir. At least one pathogen was found in 62% of the 60 diarrhea cases in winter and in 58% of the 111 diarrhea cases in fall. Multiple pathogens were found less often in winter (8%) than in fall (21%, P less than .05). Campylobacter strains were the leading cause of travelers' diarrhea in winter, found alone or with other pathogens in 28% of the cases (but in only 7% in fall), whereas enterotoxigenic Escherichia coli (ETEC) was the most common pathogen in fall, present in 32% of the cases (8% in winter). Both differences are highly significant (P less than .001). Salmonella enterica was almost as common as ETEC in fall (25% of diarrhea cases) but rare in winter (10%, P less than .05). Thus, the etiology of travelers' diarrhea varied according to the season in the same tourist destination. This finding has relevance to both antimicrobial treatment and prophylaxis.     

Maternal high fat diet and its consequence on the gut microbiome: A rat model

The biological changes that occur during pregnancy in the female mammal include shifts in hormonal regulation in preparation for parturition and lactation, and changes in energy metabolism. In women, studies have also shown that during pregnancy there is a reduction in bacterial species richness in the gut. In the current experiment rats were used to model the interaction of diet, reproductive status, and intestinal bacterial microbiota during pregnancy and lactation. In Experiment 1 rats were exposed to either standard chow or high-fat chow (60%) and were divided into two groups: unmated (NULL) or mated (RE). In Experiment 2, both NULL and RE rats were exposed to high-fat chow for a 30-day period. High-throughput sequencing of the 16S rRNA gene revealed that pregnancy impacted the gut microbiota in a similar manner to humans. The impact of reproductive status on microbiota composition, however, was stronger in rats fed a high-fat (HF) diet. Diet-induced changes replicated some of the changes observed in humans, such as increasing the Firmicutes/Bacteroidetes ratio. However, in contrast to humans, pregnancy in rats did not increase β-diversity between microbiota from different animals. These results indicate that during pregnancy in rats, the gut microbiota is altered in a similar manner to that which occurs in women, and that these changes are further exaggerated by exposure to a HF diet. Thus, the rat may allow modelling the effects of consumption of HF food during pregnancy and enable future studies to determine the risks of HF diets during pregnancy and its consequences on the offspring.     

Dysbiosis in a canine model of human fistulizing Crohn’s disease

ABSTRACT

Crohn’s disease (CD) is a chronic immune-mediated inflammatory condition caused by the loss of mucosal tolerance toward the commensal microbiota. On average, 29.5% and 42.7% CD patients experience perianal complications at 10 and 20 y after diagnosis, respectively. Perianal CD (pCD) result in high disease burden, diminished quality of life, and elevated health-care costs. Overall pCD are predictors of poor long-term outcomes. Animal models of gut inflammation have failed to fully recapitulate the human manifestations of fistulizing CD. Here, we evaluated dogs with spontaneous canine anal furunculosis (CAF), a disease with clinical similarities to pCD, as a surrogate model for understanding the microbial contribution of human pCD pathophysiology.

By comparing the gut microbiomes between dogs suffering from CAF (CAF dogs) and healthy dogs, we show CAF-dog microbiomes are either very dissimilar (dysbiotic) or similar (healthy-like), yet unique, to healthy dog’s microbiomes. Compared to healthy or healthy-like CAF microbiomes, dysbiotic CAF microbiomes showed an increased abundance of Bacteroides vulgatus and Escherichia coli and a decreased abundance of Megamonas species and Prevotella copri.

Our results mirror what have been reported in previous microbiome studies of patients with CD; particularly, CAF dogs exhibited two distinct microbiome composition: dysbiotic and healthy-like, with determinant bacterial taxa such as E. coli and P. copri that overlap what it has been found on their human counterpart. Thus, our results support the use of CAF dogs as a surrogate model to advance our understanding of microbial dynamics in pCD.     

The Microbiota and Microbiome in Aging: Potential Implications in Health and Age‐Related Diseases

Advances in bacterial deoxyribonucleic acid sequencing allow for characterization of the human commensal bacterial community (microbiota) and its corresponding genome (microbiome). Surveys of healthy adults reveal that a signature composite of bacteria characterizes each unique body habitat (e.g., gut, skin, oral cavity, vagina). A myriad of clinical changes, including a basal proinflammatory state (inflamm‐aging), that directly interface with the microbiota of older adults and enhance susceptibility to disease accompany aging. Studies in older adults demonstrate that the gut microbiota correlates with diet, location of residence (e.g., community dwelling, long‐term care settings), and basal level of inflammation. Links exist between the microbiota and a variety of clinical problems plaguing older adults, including physical frailty, Clostridium difficile colitis, vulvovaginal atrophy, colorectal carcinoma, and atherosclerotic disease. Manipulation of the microbiota and microbiome of older adults holds promise as an innovative strategy to influence the development of comorbidities associated with aging.     

Prevalence of Escherichia coli possessing the eaeA gene of enteropathogenic E. coli (EPEC) or the aggR gene of enteroaggregative E. coli (EAggEC) in traveler's diarrhea diagnosed in those returning to Tama, Tokyo from other Asian countries

To elucidate the importance of enteropathogenic Escherichia coli (EPEC) and enteroaggregative E. coli (EAggEC) as etiological agents in traveler's diarrhea, the detection of the eaeA and aggR gene in E. coli strains isolated from overseas travelers with diarrhea in Tama, Tokyo was carried out using a PCR method. Of 192 travelers who were mostly adults and had visited Asian countries from April 1998 to March 1999, aggR-positive E. coli strains were detected in 26 (13.5%). These strains represent the second predominant enteropathogen following enterotoxigenic E. coli (ETEC), whereas eaeA-positive E. coli strains were confirmed in seven subjects (3.6%). In 13 cases with aggR and four cases with eaeA, the organisms were detected in stool samples of patients as the only potential enteric pathogen. The clinical symptoms of these patients were similar to those in patients with ETEC; however, the severity of illness was milder than that associated with ETEC alone. Three strains with eaeA and five strains with aggR were typed as six different kinds of O serogroups, of which four strains belonged to the classical EPEC serogroups (O55, O114, O119, and O127a). These findings suggest that aggR-positive E. coli (EAggEC) is a significant causative agent in traveler's diarrhea. In addition, it was demonstrated that eaeA-positive E. coli (EPEC) is markedly correlated with diarrhea in adults.     

Gut microbiota profiles of autism spectrum disorder and attention deficit/hyperactivity disorder: A systematic literature review.

ABSTRACT

Accumulating evidence has implicated an involvement of the gut-brain axis in autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD), however with highly diverse results. This systematic review aims to describe and evaluate studies investigating the gut microbiota composition in individuals with ASD or ADHD and to evaluate if variations in gut microbiota are associated with these disorders.

Twenty-four articles were identified in a systematic literature search of PubMed and Embase up to July 22, 2019. They consisted of 20 studies investigating ASD and four studies investigating ADHD. For ASD, several studies agreed on an overall difference in β-diversity, although no consistent bacterial variation between all studies was reported. For ADHD, the results were more diverse, with no clear differences observed.

Several common characteristics in gut microbiota function were identified for ASD compared to controls. In contrast, highly heterogeneous results were reported for ADHD, and thus the association between gut microbiota composition and ADHD remains unclear. For both disorders, methodological differences hampered the comparison of studies.