Quantitative sequencing clarifies the role of disruptor taxa, oral microbiota, and strict anaerobes in the human small-intestine microbiome

Characterization of the Small Bowel Microbiome Reveals Different Profiles in Human Subjects Who Are Overweight or Have Obesity

INTRODUCTION

Gut microbiome changes are linked to obesity, but findings are based on stool data. In this article, we analyzed the duodenal microbiome and serum biomarkers in subjects with normal weight, overweight, and obesity.

METHODS

Duodenal aspirates and serum samples were obtained from subjects undergoing standard-of-care esophagogastroduodenoscopy without colon preparation. Aspirate DNAs were analyzed by 16S rRNA and shotgun sequencing. Predicted microbial metabolic functions and serum levels of metabolic and inflammatory biomarkers were also assessed.

RESULTS

Subjects with normal weight (N = 105), overweight (N = 67), and obesity (N = 42) were identified. Overweight-specific duodenal microbial features include lower relative abundance (RA) of Bifidobacterium species and Escherichia coli strain K-12 and higher Lactobacillus intestinalis , L. johnsonii , and Prevotella loescheii RA. Obesity-specific features include higher Lactobacillus gasseri RA and lower L. reuteri (subspecies rodentium ), Alloprevotella rava , and Leptotrichia spp RA. Escalation features (progressive changes from normal weight through obesity) include decreasing Bacteroides pyogenes , Staphylococcus hominis , and unknown Faecalibacterium species RA, increasing RA of unknown Lactobacillus and Mycobacterium species, and decreasing microbial potential for biogenic amines metabolism. De-escalation features (direction of change altered in normal to overweight and overweight to obesity) include Lactobacillus acidophilus , L. hominis , L. iners , and Bifidobacterium dentium . An unknown Lactobacillus species is associated with type IIa dyslipidemia and overweight, whereas Alloprevotella rava is associated with type IIb and IV dyslipidemias.

DISCUSSION

Direct analysis of the duodenal microbiome has identified key genera associated with overweight and obesity, including some previously identified in stool, e.g., Bifidobacterium and Lactobacillus . Specific species and strains exhibit differing associations with overweight and obesity, including escalation and de-escalation features that may represent targets for future study and therapeutics.

Fecal Coprococcus, hidden behind abdominal symptoms in patients with small intestinal bacterial overgrowth

BACKGROUND

Small intestinal bacterial overgrowth (SIBO) is the presence of an abnormally excessive amount of bacterial colonization in the small bowel. Hydrogen and methane breath test has been widely applied as a non-invasive method for SIBO. However, the positive breath test representative of bacterial overgrowth could also be detected in asymptomatic individuals.

METHODS

To explore the relationship between clinical symptoms and gut dysbiosis, and find potential fecal biomarkers for SIBO, we compared the microbial profiles between SIBO subjects with positive breath test but without abdominal symptoms (PBT) and healthy controls (HC) using 16S rRNA amplicon sequencing.

RESULTS

Fecal samples were collected from 63 SIBO who complained of diarrhea, distension, constipation, or abdominal pain, 36 PBT, and 55 HC. For alpha diversity, the Shannon index of community diversity on the genus level showed a tendency for a slight increase in SIBO, while the Shannon index on the predicted function was significantly decreased in SIBO. On the genus level, significantly decreased Bacteroides, increased Coprococcus_2, and unique Butyrivibrio were observed in SIBO. There was a significant positive correlation between saccharolytic Coprococcus_2 and the severity of abdominal symptoms. Differently, the unique Veillonella in the PBT group was related to amino acid fermentation. Interestingly, the co-occurrence network density of PBT was larger than SIBO, which indicates a complicated interaction of genera. Coprococcus_2 showed one of the largest betweenness centrality in both SIBO and PBT microbiota networks. Pathway analysis based on the Kyoto Encyclopedia of Genes and Genome (KEGG) database reflected that one carbon pool by folate and multiple amino acid metabolism were significantly down in SIBO.

CONCLUSIONS

This study provides valuable insights into the fecal microbiota composition and predicted metabolic functional changes in patients with SIBO. Butyrivibrio and Coprococcus_2, both renowned for their role in carbohydrate fermenters and gas production, contributed significantly to the symptoms of the patients. Coprococcus's abundance hints at its use as a SIBO marker. Asymptomatic PBT individuals show a different microbiome, rich in Veillonella. PBT's complex microbial interactions might stabilize the intestinal ecosystem, but further study is needed due to the core microbiota similarities with SIBO. Predicted folate and amino acid metabolism reductions in SIBO merit additional validation.

Small Intestinal Bacterial Overgrowth (SIBO), a clinically overdiagnosed entity?

Small intestinal bacterial overgrowth (SIBO) is a clinical entity recognized since ancient times; it represents the consequences of bacterial overgrowth in the small intestine associated with malabsorption. Recently, SIBO as a term has been popularized due to its high prevalence reported in various pathologies since the moment it is indirectly diagnosed with exhaled air tests. In the present article, the results of duodenal/jejunal aspirate culture testing as a reference diagnostic method, as well as the characteristics of the small intestinal microbiota described by culture-dependent and culture-independent techniques in SIBO, and their comparison with exhaled air testing are presented to argue about its overdiagnosis.

mi-Mic: a novel multi-layer statistical test for microbiota-disease associations

mi-Mic, a novel approach for microbiome differential abundance analysis, tackles the key challenges of such statistical tests: a large number of tests, sparsity, varying abundance scales, and taxonomic relationships. mi-Mic first converts microbial counts to a cladogram of means. It then applies a priori tests on the upper levels of the cladogram to detect overall relationships. Finally, it performs a Mann-Whitney test on paths that are consistently significant along the cladogram or on the leaves. mi-Mic has much higher true to false positives ratios than existing tests, as measured by a new real-to-shuffle positive score.

Small intestinal microbiota: from taxonomic composition to metabolism

The small intestinal microbiota (SIM) is essential for gastrointestinal health, influencing digestion, immune modulation, and nutrient metabolism. Unlike the colonic microbiota, the SIM has been poorly characterized due to sampling challenges and ethical considerations. Current evidence suggests that the SIM consists of five core genera and additional segment-specific taxa. These bacteria closely interact with the human host, regulating nutrient absorption and metabolism. Recent work suggests the presence of two forms of small intestinal bacterial overgrowth, one dominated by oral bacteria (SIOBO) and a second dominated by coliform bacteria. Less invasive sampling techniques, omics approaches, and mechanistic studies will allow a more comprehensive understanding of the SIM, paving the way for interventions engineering the SIM towards better health.

Defining Small Intestinal Bacterial Overgrowth by Culture and High Throughput Sequencing

BACKGROUND& AIMS

Despite accelerated research in small intestinal bacterial overgrowth (SIBO), questions remain regarding optimal diagnostic approaches and definitions. Here, we aim to define SIBO using small bowel culture and sequencing, identifying specific contributory microbes, in the context of gastrointestinal symptoms.

METHODS

Subjects undergoing esophagogastroduodenoscopy (without colonoscopy) were recruited and completed symptom severity questionnaires. Duodenal aspirates were plated on MacConkey and blood agar. Aspirate DNA was analyzed by 16S ribosomal RNA and shotgun sequencing. Microbial network connectivity for different SIBO thresholds and predicted microbial metabolic functions were also assessed.

RESULTS

A total of 385 subjects with <103 colony forming units (CFU)/mL on MacConkey agar and 98 subjects with ≥103 CFU/mL, including ≥103 to <105 CFU/mL (N = 66) and ≥105 CFU/mL (N = 32), were identified. Duodenal microbial α-diversity progressively decreased, and relative abundance of Escherichia/Shigella and Klebsiella increased, in subjects with ≥103 to <105 CFU/mL and ≥105 CFU/mL. Microbial network connectivity also progressively decreased in these subjects, driven by the increased relative abundance of Escherichia (P < .0001) and Klebsiella (P = .0018). Microbial metabolic pathways for carbohydrate fermentation, hydrogen production, and hydrogen sulfide production were enhanced in subjects with ≥103 CFU/mL and correlated with symptoms. Shotgun sequencing (N = 38) identified 2 main Escherichia coli strains and 2 Klebsiella species representing 40.24% of all duodenal bacteria in subjects with ≥103 CFU/mL.

CONCLUSIONS

Our findings confirm ≥103 CFU/mL is the optimal SIBO threshold, associated with gastrointestinal symptoms, significantly decreased microbial diversity, and network disruption. Microbial hydrogen- and hydrogen sulfide-related pathways were enhanced in SIBO subjects, supporting past studies. Remarkably few specific E coli and Klebsiella strains/species appear to dominate the microbiome in SIBO, and correlate with abdominal pain, diarrhea, and bloating severities.

Symptomatic Response to Antibiotics in Patients With Small Intestinal Bacterial Overgrowth: A Systematic Review and Meta-analysis

Background/Aims

We performed a systematic review and meta-analysis evaluating the symptomatic response rate to antibiotics in patients with small intestinal bacterial overgrowth (SIBO). Similarly, we performed a meta-analysis on the symptomatic response to antibiotics in irritable bowel syndrome (IBS) patients with and without SIBO.

Methods

MEDLINE, EMBASE, Web of Science, and Cochrane databases were searched from inception to March 2021. Randomized controlled trials and prospective studies reporting dichotomous outcomes were included.

Results

There were 6 studies included in the first meta-analysis comparing the efficacy of antibiotics to placebo or no antibiotic. This included 196 patients, of whom 101 received antibiotics and 95 received placebo or no antibiotics. Significantly more patients improved with antibiotics (relative risk [95% CI] = 2.46 [1.33-4.55], P = 0.004). There were 4 studies included in the analysis comparing symptomatic response rates in IBS patients with or without SIBO with 266 IBS patients, of whom 172 had SIBO and 94 did not. The pooled response rate for symptomatic response was 51.2% in the SIBO group vs 23.4% in the no SIBO group, respectively. Significantly more IBS patients with SIBO responded to antibiotics compared to those without SIBO (relative risk [95% CI] = 2.07 [1.40-3.08], P = 0.0003).

Conclusions

Antibiotics appear to be efficacious in treating SIBO, although small sample sizes and poor data quality limit this interpretation. Symptomatic response rates also appear to be higher in IBS patients with SIBO. This may be the first example of precision medicine in IBS as opposed to our current empiric treatment approach. Large-multicenter studies are needed to verify the results.

Consuming artificial sweeteners may alter the structure and function of duodenal microbial communities

Studies using stool samples suggest that non-sugar sweetener (NSS) consumption affects gut microbiome composition. However, stool does not represent the entire gut. We analyzed the duodenal luminal microbiome in subjects consuming non-aspartame non-sugar sweeteners (NANS, N = 35), aspartame only (ASP, N = 9), and controls (CON, N = 55) and the stool microbiome in a subset (N = 40). Duodenal alpha diversity was decreased in NANS vs. CON. Duodenal relative abundance (RA) of Escherichia, Klebsiella, and Salmonella (all phylum Proteobacteria) was lower in both NANS and ASP vs. CON, whereas stool RA of Escherichia, Klebsiella, and Salmonella was increased in both NANS and ASP vs. CON. Predicted duodenal microbial metabolic pathways altered in NANS vs. CON included polysaccharides biosynthesis and D-galactose degradation, whereas cylindrospermopsin biosynthesis was significantly enriched in ASP vs. CON. These findings suggest that consuming non-sugar sweeteners may significantly alter microbiome composition and function in the metabolically active small bowel, with different alterations seen in stool.

Coronavirus Disease 2019 (COVID-19) Pandemic Lifestyle Changes May Have Influenced Small Bowel Microbial Composition and Microbial Resistance

BACKGROUND

The coronavirus disease 2019 (COVID-19) global pandemic necessitated many severe lifestyle changes, including lockdowns, social distancing, altered food consumption and exercise patterns, and extensive hygiene practices. These extensive changes may have affected the human gut microbiome, which is highly influenced by lifestyle.

AIMS

To examine the potential effects of pandemic-related lifestyle changes on the metabolically relevant small bowel microbiome.

METHODS

Adult subjects presenting for upper endoscopy without colonoscopy were identified and divided into two matched groups: pre-pandemic (February 2019-March 2020) and intra-pandemic (April 2021-September 2021, all COVID-19 negative). Duodenal aspirates and blood samples were collected. Duodenal microbiomes were analyzed by 16S rRNA sequencing. Serum cytokine levels were analyzed by Luminex FlexMap3D.

RESULTS

Fifty-six pre-pandemic and 38 COVID-negative intra-pandemic subjects were included. There were no significant changes in duodenal microbial alpha diversity in the intra-pandemic vs. pre-pandemic group, but beta diversity was significantly different. The relative abundance (RA) of phylum Deinococcus-Thermus and family Thermaceae, which are resistant extremophiles, was significantly higher in the intra-pandemic vs. pre-pandemic group. The RA of several Gram-negative taxa including Bacteroidaceae (phylum Bacteroidetes) and the Proteobacteria families Enterobacteriaceae and Pseudomonadaceae, and the RA of potential disruptor genera Escherichia-Shigella and Rothia, were significantly lower in the intra-pandemic vs. pre-pandemic group. Circulating levels of interleukin-18 were also lower in the intra-pandemic group.

CONCLUSIONS

These findings suggest the small bowel microbiome underwent significant changes during the pandemic, in COVID-19-negative individuals. Given the key roles of the small bowel microbiota in host physiology, this may have implications for human health.

Quantitative whole-tissue 3D imaging reveals bacteria in close association with mouse jejunum mucosa

Because the small intestine (SI) epithelium lacks a thick protective mucus layer, microbes that colonize the thin SI mucosa may exert a substantial effect on the host. For example, bacterial colonization of the human SI may contribute to environmental enteropathy dysfunction (EED) in malnourished children. Thus far, potential bacterial colonization of the mucosal surface of the SI has only been documented in disease states, suggesting mucosal colonization is rare, likely requiring multiple perturbations. Furthermore, conclusive proof of bacterial colonization of the SI mucosal surface is challenging, and the three-dimensional (3D) spatial structure of mucosal colonies remains unknown. Here, we tested whether we could induce dense bacterial association with jejunum mucosa by subjecting mice to a combination of malnutrition and oral co-gavage with a bacterial cocktail (E. coli and Bacteroides spp.) known to induce EED. To visualize these events, we optimized our previously developed whole-tissue 3D imaging tools with third-generation hybridization chain reaction (HCR v3.0) probes. Only in mice that were malnourished and gavaged with the bacterial cocktail did we detect dense bacterial clusters surrounding intestinal villi suggestive of colonization. Furthermore, in these mice we detected villus loss, which may represent one possible consequence that bacterial colonization of the SI mucosa has on the host. Our results suggest that dense bacterial colonization of jejunum mucosa is possible in the presence of multiple perturbations and that whole-tissue 3D imaging tools can enable the study of these rare events.

Phage therapy in gut microbiome

Phage therapy, the use of bacteriophage viruses for bacterial infection treatment, has been around for almost a century, but with the increase in antibiotic use, its importance has declined rapidly. There has been renewed interest in revisiting this practice due to the general decline in the effectiveness of antibiotics, combined with improved understanding of human microbiota and advances in sequencing technologies. Phage therapy has been proposed as a clinical alternative to restore the gut microbiota in the absence of an effective treatment. That is due to its immunomodulatory and bactericidal effects against its target bacteria. In the gastrointestinal diseases field, phage therapy has been studied mainly as a promising tool in infectious diseases treatment, such as cholera and diarrhea. However, many studies have been conducted in non-communicable diseases, such as the targeting of adherent invasive Escherichia coli in Crohn's disease, the treatment of Clostridioides difficile in ulcerative colitis, the eradication of Fusobacterium nucleatum in colorectal cancer, the targeting of alcohol-producing Klebsiella pneumoniae in non-alcoholic fatty liver disease, or Enterococcus faecalis in alcohol-associated hepatitis. This review will summarize the changes in the gut microbiota and the phageome in association with some gastrointestinal and liver diseases and highlight the recent scientific advances in phage therapy as a therapeutic tool for their treatment.

Unravelling the controversy with small intestinal bacterial overgrowth

PURPOSE OF REVIEW

The aim of this review is to summarize the current and emergent approaches to characterize the small intestinal microbiota and discuss the treatment options for management of small intestinal bacterial overgrowth (SIBO).

RECENT FINDINGS

This review captures the growing body of evidence for the role of SIBO, a type of small intestinal dysbiosis in the pathophysiology various gastrointestinal and extraintestinal disorders. We have highlighted the drawbacks of the available methods for characterizing the small intestinal microbiota and focus on the new culture-independent techniques to diagnose SIBO. Although recurrence is common, targeted modulation of the gut microbiome as a therapeutic option for management of SIBO is associated with improvement in symptoms and quality of life.

SUMMARY

As a first step to precisely characterize the potential link between SIBO and various disorders, we need to address the methodological limitations of the available traditional tests for diagnosing SIBO. There is an urgency to develop culture independent techniques that can be routinely used in clinical setting, that will enable characterization of the gastrointestinal microbiome and explore the response to antimicrobial therapy including the links between long-lasting symptom resolution and the microbiome.

Colonization resistance is dispensable for segregation of oral and gut microbiota

BACKGROUND

The oral and colonic microbiota are distinct in healthy individuals. However, this distinction is diminished in common diseases such as colon cancer and inflammatory bowel disease, suggesting a potential pathogenic role for oral bacteria when ectopically colonized in the gut. A key mechanism for the segregation of oral and colonic microbiota niches is thought to be microbiota-mediated colonization resistance whereby the commensal gut microbiota outcompete and eliminate the ingested oral bacteria.

METHODS

We tested this theory by analyzing exact amplicon sequence variants generated from concurrent fecal and oral samples from healthy volunteers exposed to a brief course of a single antibiotic (cohort 1), acute leukemia patients (cohort 2), and stem cell transplant recipients (cohort 3). Cohorts 2 and 3 represent extreme clinical scenarios with respect to antibiotic pressure and severity of gut microbiota injury.

RESULTS

While mild antibiotic exposure in cohort 1 was not sufficient for colonization of any oral bacteria in the gut, even with extreme antibiotic pressure and severe gut microbiota disruptions in cohorts 2 and 3, only one oral species in each cohort colonized the gut.

CONCLUSIONS

Colonization resistance is dispensable for segregation of oral and colonic microbiota in humans. This finding implies that the presence of oral bacteria in the distal gut in diseases such as colon cancer and inflammatory bowel disease is not driven by impaired colonization resistance.

Higher yield in duodenoscope cultures collected with addition of neutralizing agent

AIM

Microbiological cultures are the gold standard in the monitoring of duodenoscope reprocessing. However, many different sampling and culturing techniques are used, making it difficult to compare results. The latest Centers for Disease Control and Prevention protocol advises the use of a neutralizer to deactivate any remaining disinfectants in the samples. This study compared culturing results of duodenoscope samples collected with and without addition of a neutralizer.

METHODS

Six duodenoscopes were soiled with gut bacteria in a non-clinical experimental setting and reprocessed afterwards. Samples of the tip and working channel were collected immediately after decontamination or after drying. Dey-Engley (DE) broth was added as a neutralizer to the samples of four duodenoscopes; samples for the other two duodenoscopes were collected without the addition of DE broth.

RESULTS

Post-decontamination cultures were significantly more likely to be positive for growth of the applied micro-organisms in the group of samples with DE broth (88.1% vs 20.2%; P<0.0001). Post-drying samples were significantly more likely to be positive in the group of samples without DE broth (75.7% vs 33.4%; P<0.001).

CONCLUSION

The addition of DE broth to samples collected from wet duodenoscopes increases the yield of those cultures. Remaining disinfectants in wet duodenoscopes can lead to false-negative results. This can be overcome by adding a neutralizer, such as DE broth, to the samples. The higher yield after drying in the group without neutralizer could be due to biofilm formation in these two duodenoscopes, but this was not investigated. Standardization of the sampling method can help to compare both clinical and study results regarding duodenoscope contamination.

Regulatory effects of oral microbe on intestinal microbiota and the illness

Over the past decade, the association between oral health, intestinal microbiota, and systemic diseases has been further validated. Some oral microbial species have been isolated from pathological intestine mucosa or feces and identified as biomarkers for intestinal diseases. A small proportion of oral microbiome passes through or colonizes the lower gastrointestinal tract, even in healthy individuals. Opportunistic pathogens from the oral cavity may expand and participate in the occurrence and progression of intestinal diseases when the anatomical barrier is disrupted. These disruptors interact with the intestinal microbiota, disturbing indigenous microorganisms, and mucosal barriers through direct colonization, blood circulation, or derived metabolite pathways. While interacting with the host's immune system, oral-derived pathogens stimulate inflammation responses and guide the transition of the intestinal microenvironment from a healthy state to a pre-disease state. Therefore, the oral-gut microbiome axis sheds light on new clinical therapy options, and gastrointestinal tract ecology balance necessitates simultaneous consideration of both oral and gut microbiomes. This review summarizes possible routes of oral microbes entering the intestine and the effects of certain oral bacteria on intestinal microbiota and the host's immune responses.

GATA4 controls regionalization of tissue immunity and commensal-driven immunopathology

There is growing recognition that regionalization of bacterial colonization and immunity along the intestinal tract has an important role in health and disease. Yet, the mechanisms underlying intestinal regionalization and its dysregulation in disease are not well understood. This study found that regional epithelial expression of the transcription factor GATA4 controls bacterial colonization and inflammatory tissue immunity in the proximal small intestine by regulating retinol metabolism and luminal IgA. Furthermore, in mice without jejunal GATA4 expression, the commensal segmented filamentous bacteria promoted pathogenic inflammatory immune responses that disrupted barrier function and increased mortality upon Citrobacter rodentium infection. In celiac disease patients, low GATA4 expression was associated with metabolic alterations, mucosal Actinobacillus, and increased IL-17 immunity. Taken together, these results reveal broad impacts of GATA4-regulated intestinal regionalization on bacterial colonization and tissue immunity, highlighting an elaborate interdependence of intestinal metabolism, immunity, and microbiota in homeostasis and disease.

Identifying oral microbiome alterations in adult betel quid chewing population of Delhi, India

The study targets to establish a factorial association of oral microbiome alterations (oral dysbiosis) with betel quid chewing habits through a comparison of the oral microbiome of Betel quid chewers and non-chewing individuals. Oral microbiome analysis of 22 adult individuals in the Delhi region of India through the 16S sequencing approach was carried out to observe the differences in taxonomic abundance and diversity. A significant difference in diversity and richness among Betel Quid Chewers (BQC) and Betel Quid Non-Chewers (BQNC) groups was observed. There were significant differences in alpha diversity among the BQC in comparison to BQNC. However, in the age group of 21-30 years old young BQC and BQNC there was no significant difference in alpha diversity. Similar result was obtained while comparing BQC and Smoker-alcoholic BQC. BQ smoker-chewers expressed significant variance in comparison to BQC, based on cluster pattern analysis. The OTU-based Venn Diagram Analysis revealed an altered microbiota, for BQ chewing group with 0-10 years exposure in comparison to those with 10 years and above. The change in the microbial niche in early chewers may be due to abrupt chemical component exposure affecting the oral cavity, and thereafter establishing a unique microenvironment in the long-term BQC. Linear discriminant analysis revealed, 55 significant features among BQC and Alcoholic-Smoker BQC; and 20 significant features among BQC and Smoker BQC respectively. The study shows the abundance of novel bacterial genera in the BQC oral cavity in addition to the commonly found ones. Since the oral microbiome plays a significant role in maintaining local homeostasis, investigating the link between its imbalance in such conditions that are known to have an association with oral diseases including cancers may lead to the identification of specific microbiome-based signatures for its early diagnosis.

Type 2 Diabetes and the Microbiome

Diabetes represents one of the most significant, and rapidly escalating, global healthcare crises we face today. Diabetes already affects one-tenth of the world's adults-more than 537 million people, numbers that have tripled since 2000 and are estimated to reach 643 million by 2030. Type 2 diabetes (T2D), the most prevalent form, is a complex disease with numerous contributing factors, including genetics, epigenetics, diet, lifestyle, medication use, and socioeconomic factors. In addition, the gut microbiome has emerged as a significant potential contributing factor in T2D development and progression. Gut microbes and their metabolites strongly influence host metabolism and immune function, and are now known to contribute to vitamin biosynthesis, gut hormone production, satiety, maintenance of gut barrier integrity, and protection against pathogens, as well as digestion and nutrient absorption. In turn, gut microbes are influenced by diet and lifestyle factors such as alcohol and medication use, including antibiotic use and the consumption of probiotics and prebiotics. Here we review current evidence regarding changes in microbial populations in T2D and the mechanisms by which gut microbes influence glucose metabolism and insulin resistance, including inflammation, gut permeability, and bile acid production. We also explore the interrelationships between gut microbes and different T2D medications and other interventions, including prebiotics, probiotics, and bariatric surgery. Lastly, we explore the particular role of the small bowel in digestion and metabolism and the importance of studying small bowel microbes directly in our search to find metabolically relevant biomarkers and therapeutic targets for T2D.

Elevated salivary kynurenic acid levels related to enlarged choroid plexus and severity of clinical phenotypes in treatment-resistant schizophrenia

Patients with treatment-resistant schizophrenia (TRS) suffer severe, long-term psychotic symptoms and chronic stress. Salivary kynurenic acid (KYNA) and choroid plexus were evidenced to relate to psychological stress. We hypothesized that TRS patients would have higher salivary KYNA levels than patients who respond to antipsychotics (NTRS) and healthy controls (HC), and increased salivary KYNA levels are associated with clinical phenotypes and choroid plexus volume. A total of 66 HC participants, 53 patients with TRS and 46 with NTRS were enrolled. Salivary KYNA levels were measured by liquid chromatography-tandem mass spectrometry, choroid plexus volume by magnetic resonance imaging, and cognitive functions with the MATRICS Consensus Cognitive Battery. The TRS group had significantly higher salivary KYNA levels than the NTRS group (p = 0.003), who in turn had higher salivary KYNA than HC (p = 0.02). Higher salivary KYNA levels were associated with larger choroid plexus volume (r = 0.48, p = 0.004); lower attention/vigilance (r = -0.44, p = 0.004), verbal learning (r = -0.44, p = 0.004), total MCCB score (r = -0.42, p = 0.005); and a higher total PANSS score (r = 0.48, p = 0.004) in TRS patients. An enlarged choroid plexus also related to worse attention/vigilance (r = -0.39, p = 0.03), verbal learning (r = -0.55, p = 0.001), total MCCB score (r = -0.41, p = 0.02) and clinical symptoms (r = 0.48, p = 0.004) in TRS patients only. We conclude that elevated salivary KYNA levels and associated choroid plexus enlargement are clinically relevant indicators of TRS, with salivary KYNA being particularly valuable as a peripheral marker. Our findings should benefit TRS research and benefit the improvement of personalized treatment.

Microbiome-based interventions to modulate gut ecology and the immune system

The gut microbiome lies at the intersection between the environment and the host, with the ability to modify host responses to disease-relevant exposures and stimuli. This is evident in how enteric microbes interact with the immune system, e.g., supporting immune maturation in early life, affecting drug efficacy via modulation of immune responses, or influencing development of immune cell populations and their mediators. Many factors modulate gut ecosystem dynamics during daily life and we are just beginning to realise the therapeutic and prophylactic potential of microbiome-based interventions. These approaches vary in application, goal, and mechanisms of action. Some modify the entire community, such as nutritional approaches or faecal microbiota transplantation, while others, such as phage therapy, probiotics, and prebiotics, target specific taxa or strains. In this review, we assessed the experimental evidence for microbiome-based interventions, with a particular focus on their clinical relevance, ecological effects, and modulation of the immune system.

Periodontitis Salivary Microbiota Aggravates Ischemic Stroke Through IL-17A

Although epidemiological studies suggest that periodontitis is tightly associated with ischemic stroke, its impact on ischemic stroke and the underlysing mechanisms are poorly understood. Recent studies have shown that alteration in gut microbiota composition influences the outcomes of ischemic stroke. In the state of periodontitis, many oral pathogenic bacteria in the saliva are swallowed and transmitted to the gut. However, the role of periodontitis microbiota in the pathogenesis and progression of ischemic stroke is unclear. Therefore, we hypothesized that the periodontitis salivary microbiota influences the gut immune system and aggravates ischemic stroke. Mice receiving gavage of periodontitis salivary microbiota showed significantly worse stroke outcomes. And these mice also manifested more severe neuroinflammation, with higher infiltration of inflammatory cells and expression of inflammatory cytokines in the ischemic brain. More accumulation of Th17 cells and IL-17⁺ γδ T cells were observed in the ileum. And in Kaede transgenic mice after photoconversion. Migration of CD4⁺ T cells and γδ T cells from the ileum to the brain was observed after ischemic stroke in photoconverted Kaede transgenic mice. Furthermore, the worse stroke outcome was abolished in the IL-17A knockout mice. These findings suggest that periodontitis salivary microbiota increased IL-17A-producing immune cells in the gut, likely promoted the migration of these cells from the gut to the brain, and subsequently provoked neuroinflammation after ischemic stroke. These findings have revealed the role of periodontitis in ischemic stroke through the gut and provided new insights into the worse outcome of ischemic stroke coexisting with periodontitis in clinical trials.

Current and Future Approaches for Diagnosing Small Intestinal Dysbiosis in Patients With Symptoms of Functional Dyspepsia

The development and application of next generation sequencing technologies for clinical gastroenterology research has provided evidence that microbial dysbiosis is of relevance for the pathogenesis of gastrointestinal and extra-intestinal diseases. Microbial dysbiosis is characterized as alterations of diversity, function, and density of the intestinal microbes. Emerging evidence suggests that alterations of the gastrointestinal microbiome are important for the pathophysiology of a variety of functional gastrointestinal conditions, e.g., irritable bowel syndrome (IBS) and functional dyspepsia (FD), also known as disorders of brain-gut axis interaction. Clinicians have for many years recognized that small intestinal bacterial overgrowth (SIBO) is typified by a microbial dysbiosis that is underpinned by abnormal bacterial loads in these sites. SIBO presents with symptoms which overlap with symptoms of FD and IBS, point toward the possibility that SIBO is either the cause or the consequence of functional gastrointestinal disorders (FGIDs). More recently, new terms including “intestinal methanogen overgrowth” and “small intestinal fungal overgrowth” have been introduced to emphasize the contribution of methane production by archea and fungi in small intestinal dysbiosis. There is emerging data that targeted antimicrobial treatment of SIBO in patients with FD who simultaneously may or may not have IBS, results in symptom improvement and normalization of positive breath tests. However, the association between SIBO and FGIDs remains controversial, since widely accepted diagnostic tests for SIBO are lacking. Culture of jejunal fluid aspirate has been proposed as the “traditional gold standard” for establishing the diagnosis of SIBO. Utilizing jejunal fluid culture, the results can potentially be affected by cross contamination from oropharyngeal and luminal microbes, and there is controversy regarding the best cut off values for SIBO diagnosis. Thus, it is rarely used in routine clinical settings. These limitations have led to the development of breath tests, which when compared with the “traditional gold standard,” have sub-optimal sensitivity and specificity for SIBO diagnosis. With newer diagnostic approaches–based upon applications of the molecular techniques there is an opportunity to characterize the duodenal and colonic mucosa associated microbiome and associated gut microbiota dysbiosis in patients with various gastrointestinal and extraintestinal diseases. Furthermore, the role of confounders like psychological co-morbidities, medications, dietary practices, and environmental factors on the gastrointestinal microbiome in health and disease also needs to be explored.

Gut microbiome and health: mechanistic insights

The gut microbiota is now considered as one of the key elements contributing to the regulation of host health. Virtually all our body sites are colonised by microbes suggesting different types of crosstalk with our organs. Because of the development of molecular tools and techniques (ie, metagenomic, metabolomic, lipidomic, metatranscriptomic), the complex interactions occurring between the host and the different microorganisms are progressively being deciphered. Nowadays, gut microbiota deviations are linked with many diseases including obesity, type 2 diabetes, hepatic steatosis, intestinal bowel diseases (IBDs) and several types of cancer. Thus, suggesting that various pathways involved in immunity, energy, lipid and glucose metabolism are affected.In this review, specific attention is given to provide a critical evaluation of the current understanding in this field. Numerous molecular mechanisms explaining how gut bacteria might be causally linked with the protection or the onset of diseases are discussed. We examine well-established metabolites (ie, short-chain fatty acids, bile acids, trimethylamine N-oxide) and extend this to more recently identified molecular actors (ie, endocannabinoids, bioactive lipids, phenolic-derived compounds, advanced glycation end products and enterosynes) and their specific receptors such as peroxisome proliferator-activated receptor alpha (PPARα) and gamma (PPARγ), aryl hydrocarbon receptor (AhR), and G protein-coupled receptors (ie, GPR41, GPR43, GPR119, Takeda G protein-coupled receptor 5).Altogether, understanding the complexity and the molecular aspects linking gut microbes to health will help to set the basis for novel therapies that are already being developed.

Gut microbiome and health: mechanistic insights

The gut microbiota is now considered as one of the key elements contributing to the regulation of host health. Virtually all our body sites are colonised by microbes suggesting different types of crosstalk with our organs. Because of the development of molecular tools and techniques (ie, metagenomic, metabolomic, lipidomic, metatranscriptomic), the complex interactions occurring between the host and the different microorganisms are progressively being deciphered. Nowadays, gut microbiota deviations are linked with many diseases including obesity, type 2 diabetes, hepatic steatosis, intestinal bowel diseases (IBDs) and several types of cancer. Thus, suggesting that various pathways involved in immunity, energy, lipid and glucose metabolism are affected.In this review, specific attention is given to provide a critical evaluation of the current understanding in this field. Numerous molecular mechanisms explaining how gut bacteria might be causally linked with the protection or the onset of diseases are discussed. We examine well-established metabolites (ie, short-chain fatty acids, bile acids, trimethylamine N-oxide) and extend this to more recently identified molecular actors (ie, endocannabinoids, bioactive lipids, phenolic-derived compounds, advanced glycation end products and enterosynes) and their specific receptors such as peroxisome proliferator-activated receptor alpha (PPARα) and gamma (PPARγ), aryl hydrocarbon receptor (AhR), and G protein-coupled receptors (ie, GPR41, GPR43, GPR119, Takeda G protein-coupled receptor 5).Altogether, understanding the complexity and the molecular aspects linking gut microbes to health will help to set the basis for novel therapies that are already being developed.

Smoking has disruptive effects on the small bowel luminal microbiome

Tobacco use is the leading preventable cause of cancer, and affects the respiratory, oral, fecal, and duodenal mucosa-associated microbiota. However, the effects of smoking on the duodenal luminal microbiome have not been studied directly. We aimed to compare the duodenal luminal microbiome in never-smokers, current smokers, and ex-smokers who quit ≥ 10 years ago. In a cross-sectional study, current smokers (CS, n = 24) were identified and matched to never-smokers (NS, n = 27) and ex-smokers (XS, n = 27) by age (± 5 years), body mass index (BMI, ± 3 kg/m²), and sex. Current antibiotic users were excluded. The duodenal luminal microbiome was analysed in 1 aspirate sample per subject by 16S rRNA gene sequencing. Relative abundances (RA) of families associated with increased duodenal microbial diversity, Prevotellaceae, Neisseriaceae, and Porphyromonadaceae, were significantly lower in CS vs. NS. This was driven by lower RA of unknown Prevotella and Porphyromonas species, and Neisseria subflava and N. cinerea, in CS. In contrast, RA of Enterobacteriaceae and Lactobacillaceae (associated with decreased diversity), were significantly higher in CS, due to higher RA of Escherichia-Shigella, Klebsiella and Lactobacillus species. Many of these changes were absent or less pronounced in XS, who exhibited a duodenal luminal microbiome more similar to NS. RA of taxa previously found to be increased in the oral and respiratory microbiota of smokers were also higher in the duodenal luminal microbiome, including Bulledia extructa and an unknown Filifactor species. In conclusion, smoking is associated with an altered duodenal luminal microbiome. However, ex-smokers have a duodenal luminal microbiome that is similar to never-smokers.

The Role of the Oral Microbiota Related to Periodontal Diseases in Anxiety, Mood and Trauma- and Stress-Related Disorders

The prevalence of anxiety, mood and trauma- and stress-related disorders are on the rise; however, efforts to develop new and effective treatment strategies have had limited success. To identify novel therapeutic targets, a comprehensive understanding of the disease etiology is needed, especially in the context of the holobiont, i.e., the superorganism consisting of a human and its microbiotas. Much emphasis has been placed on the role of the gut microbiota in the development, exacerbation, and persistence of psychiatric disorders; however, data for the oral microbiota are limited. The oral cavity houses the second most diverse microbial community in the body, with over 700 bacterial species that colonize the soft and hard tissues. Periodontal diseases encompass a group of infectious and inflammatory diseases that affect the periodontium. Among them, periodontitis is defined as a chronic, multi-bacterial infection that elicits low-grade systemic inflammation via the release of pro-inflammatory cytokines, as well as local invasion and long-distance translocation of periodontal pathogens. Periodontitis can also induce or exacerbate other chronic systemic inflammatory diseases such as atherosclerosis and diabetes and can lead to adverse pregnancy outcomes. Recently, periodontal pathogens have been implicated in the etiology and pathophysiology of neuropsychiatric disorders (such as depression and schizophrenia), especially as dysregulation of the immune system also plays an integral role in the etiology and pathophysiology of these disorders. This review will discuss the role of the oral microbiota associated with periodontal diseases in anxiety, mood and trauma- and stress-related disorders. Epidemiological data of periodontal diseases in individuals with these disorders will be presented, followed by a discussion of the microbiological and immunological links between the oral microbiota and the central nervous system. Pre-clinical and clinical findings on the oral microbiota related to periodontal diseases in anxiety, mood and trauma- and stress-related phenotypes will be reviewed, followed by a discussion on the bi-directionality of the oral-brain axis. Lastly, we will focus on the oral microbiota associated with periodontal diseases as a target for future therapeutic interventions to alleviate symptoms of these debilitating psychiatric disorders.