Dietary carbohydrates regulate intestinal colonization and dissemination of Klebsiella pneumoniae

Bacterial translocation from the gut microbiota is a source of sepsis in susceptible patients. Previous work suggests that overgrowth of gut pathobionts, including Klebsiella pneumoniae, increases the risk of disseminated infection. Our data from a human dietary intervention study found that, in the absence of fiber, K. pneumoniae bloomed during microbiota recovery from antibiotic treatment. We thus hypothesized that dietary nutrients directly support or suppress colonization of this gut pathobiont in the microbiota. Consistent with our study in humans, complex carbohydrates in dietary fiber suppressed the colonization of K. pneumoniae and allowed for recovery of competing commensals in mouse models. In contrast, through ex vivo and in vivo modeling, we identified simple carbohydrates as a limiting resource for K. pneumoniae in the gut. As proof of principle, supplementation with lactulose, a nonabsorbed simple carbohydrate and an FDA-approved therapy, increased colonization of K. pneumoniae. Disruption of the intestinal epithelium led to dissemination of K. pneumoniae into the bloodstream and liver, which was prevented by dietary fiber. Our results show that dietary simple and complex carbohydrates were critical not only in the regulation of pathobiont colonization but also disseminated infection, suggesting that targeted dietary interventions may offer a preventative strategy in high-risk patients.

Changes in fecal lipidome after treatment with ivacaftor without changes in microbiome or bile acids

BACKGROUND

Alterations in gastrointestinal health are prominent manifestations of cystic fibrosis (CF) and can independently impact pulmonary function. Ivacaftor has been associated with robust improvements in pulmonary function and weight gain, but less is known about the impact of ivacaftor on the fecal microbiome, lipidome, and bile acids.

METHODS

Stool samples from 18 patients with CF and gating mutations (ages 6-61 years, 13 pancreatic insufficient) were analyzed for fecal microbiome and lipidome composition as well as bile acid concentrations at baseline and after 3 months of treatment with ivacaftor. Microbiome composition was also assessed in a healthy reference cohort.

RESULTS

Alpha and beta diversity of the microbiome were different between CF and reference cohort at baseline, but no treatment effect was seen in the CF cohort between baseline and 3 months. Seven lipids increased with treatment. No differences were seen in bile acid concentrations after treatment in CF. At baseline, 403 lipids and unconjugated bile acids were different between pancreatic insufficient (PI-CF) and sufficient (PS-CF) groups and 107 lipids were different between PI-CF and PS-CF after 3 months of treatment.

CONCLUSIONS

The composition and diversity of the fecal microbiome were different in CF as compared to a healthy reference, and did not change after 3 months of ivacaftor. We detected modest differences in the fecal lipidome with treatment. Differences in lipid and bile acid profiles between PS-CF and PI-CF were attenuated after 3 months of treatment.

Enterobacteriaceae Growth Promotion by Intestinal Acylcarnitines, a Biomarker of Dysbiosis in Inflammatory Bowel Disease

BACKGROUND & AIMS

Altered plasma acylcarnitine levels are well-known biomarkers for a variety of mitochondrial fatty acid oxidation disorders and can be used as an alternative energy source for the intestinal epithelium when short-chain fatty acids are low. These membrane-permeable fatty acid intermediates are excreted into the gut lumen via bile and are increased in the feces of patients with inflammatory bowel disease (IBD).

METHODS

Herein, based on studies in human subjects, animal models, and bacterial cultures, we show a strong positive correlation between fecal carnitine and acylcarnitines and the abundance of Enterobacteriaceae in IBD where they can be consumed by bacteria both in vitro and in vivo.

RESULTS

Carnitine metabolism promotes the growth of Escherichia coli via anaerobic respiration dependent on the cai operon, and acetylcarnitine dietary supplementation increases fecal carnitine levels with enhanced intestinal colonization of the enteric pathogen Citrobacter rodentium.

CONCLUSIONS

In total, these results indicate that the increased luminal concentrations of carnitine and acylcarnitines in patients with IBD may promote the expansion of pathobionts belonging to the Enterobacteriaceae family, thereby contributing to disease pathogenesis.

Colonization and Dissemination of Klebsiella pneumoniae is Dependent on Dietary Carbohydrates

Dysbiosis of the gut microbiota is increasingly appreciated as both a consequence and precipitant of human disease. The outgrowth of the bacterial family Enterobacteriaceae is a common feature of dysbiosis, including the human pathogen Klebsiella pneumoniae . Dietary interventions have proven efficacious in the resolution of dysbiosis, though the specific dietary components involved remain poorly defined. Based on a previous human diet study, we hypothesized that dietary nutrients serve as a key resource for the growth of bacteria found in dysbiosis. Through human sample testing, and ex-vivo , and in vivo modeling, we find that nitrogen is not a limiting resource for the growth of Enterobacteriaceae in the gut, contrary to previous studies. Instead, we identify dietary simple carbohydrates as critical in colonization of K. pneumoniae . We additionally find that dietary fiber is necessary for colonization resistance against K. pneumoniae , mediated by recovery of the commensal microbiota, and protecting the host against dissemination from the gut microbiota during colitis. Targeted dietary therapies based on these findings may offer a therapeutic strategy in susceptible patients with dysbiosis.

IgA deficiency destabilizes homeostasis toward intestinal microbes and increases systemic immune dysregulation

The ability of most patients with selective immunoglobulin A (IgA) deficiency (SIgAD) to remain apparently healthy has been a persistent clinical conundrum. Compensatory mechanisms, including IgM, have been proposed, yet it remains unclear how secretory IgA and IgM work together in the mucosal system and, on a larger scale, whether the systemic and mucosal anti-commensal responses are redundant or have unique features. To address this gap in knowledge, we developed an integrated host-commensal approach combining microbial flow cytometry and metagenomic sequencing (mFLOW-Seq) to comprehensively define which microbes induce mucosal and systemic antibodies. We coupled this approach with high-dimensional immune profiling to study a cohort of pediatric patients with SIgAD and household control siblings. We found that mucosal and systemic antibody networks cooperate to maintain homeostasis by targeting a common subset of commensal microbes. In IgA-deficiency, we find increased translocation of specific bacterial taxa associated with elevated levels of systemic IgG targeting fecal microbiota. Associated features of immune system dysregulation in IgA-deficient mice and humans included elevated levels of inflammatory cytokines, enhanced follicular CD4 T helper cell frequency and activation, and an altered CD8 T cell activation state. Although SIgAD is clinically defined by the absence of serum IgA, the symptomatology and immune dysregulation were concentrated in the SIgAD participants who were also fecal IgA deficient. These findings reveal that mucosal IgA deficiency leads to aberrant systemic exposures and immune responses to commensal microbes, which increase the likelihood of humoral and cellular immune dysregulation and symptomatic disease in patients with IgA deficiency.

Lacticaseibacillus rhamnosus Strain GG (LGG) Regulate Gut Microbial Metabolites, an In Vitro Study Using Three Mature Human Gut Microbial Cultures in a Simulator of Human Intestinal Microbial Ecosystem (SHIME)

In the present research, we investigated changes in the gut metabolome that occurred in response to the administration of the Laticaseibacillus rhamnosus strain GG (LGG). The probiotics were added to the ascending colon region of mature microbial communities established in a human intestinal microbial ecosystem simulator. Shotgun metagenomic sequencing and metabolome analysis suggested that the changes in microbial community composition corresponded with changes to metabolic output, and we can infer linkages between some metabolites and microorganisms. The in vitro method permits a spatially-resolved view of metabolic transformations under human physiological conditions. By this method, we found that tryptophan and tyrosine were mainly produced in the ascending colon region, while their derivatives were detected in the transverse and descending regions, revealing sequential amino acid metabolic pathways along with the colonic tract. The addition of LGG appeared to promote the production of indole propionic acid, which is positively associated with human health. Furthermore, the microbial community responsible for the production of indole propionic acid may be broader than is currently known.

Persistence of the Probiotic Lacticaseibacillus rhamnosus Strain GG (LGG) in an In Vitro Model of the Gut Microbiome

The consumption of probiotics is widely encouraged due to reports of their positive effects on human health. In particular, Lacticaseibacillus rhamnosus strain GG (LGG) is an approved probiotic that has been reported to improve health outcomes, especially for gastrointestinal disorders. However, how LGG cooperates with the gut microbiome has not been fully explored. To understand the interaction between LGG and its ability to survive and grow within the gut microbiome, this study introduced LGG into established microbial communities using an in vitro model of the colon. LGG was inoculated into the simulated ascending colon and its persistence in, and transit through the subsequent transverse and descending colon regions was monitored over two weeks. The impact of LGG on the existing bacterial communities was investigated using 16S rRNA sequencing and short-chain fatty acid analysis. LGG was able to engraft and proliferate in the ascending region for at least 10 days but was diminished in the transverse and descending colon regions with little effect on short-chain fatty acid abundance. These data suggest that the health benefits of the probiotic LGG rely on its ability to transiently engraft and modulate the host microbial community.

SARS-CoV-2-specific T cells in unexposed adults display broad trafficking potential and cross-react with commensal antigens

The baseline composition of T cells directly affects later response to pathogens, but the complexity of precursor states remains poorly defined. Here, we examined the baseline state of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific T cells in unexposed individuals. SARS-CoV-2-specific CD4+ T cells were identified in prepandemic blood samples by major histocompatibility complex (MHC) class II tetramer staining and enrichment. Our data revealed a substantial number of SARS-CoV-2-specific T cells that expressed memory phenotype markers. Integrated phenotypic analyses demonstrated diverse preexisting memory states that included cells with distinct polarization features and trafficking potential to barrier tissues. T cell clones generated from tetramer-labeled cells cross-reacted with antigens from commensal bacteria in the skin and gastrointestinal tract. Direct ex vivo tetramer staining for one spike-specific population showed a similar level of cross-reactivity to sequences from endemic coronavirus and commensal bacteria. These data highlight the complexity of precursor T cell repertoire and implicate noninfectious exposures to common microbes as a key factor that shapes human preexisting immunity to SARS-CoV-2.

A Microbial Signature for Paediatric Perianal Crohn's Disease

BACKGROUND AND AIMS

Perianal fistulising disease can affect up to 25% of patients with Crohn's disease [CD] and lead to significant morbidity. Although the role of the gut microbiota in inflammatory bowel disease [IBD] has been increasingly recognised, its role in fistula development has scarcely been studied. Here, we aimed to define the microbial signature associated with perianal fistulising CD in children.

METHODS

A prospective observational study including children age 6-18 years with a diagnosis of perianal fistulising CD was conducted. Stool samples and rectal and perianal fistula swabs were collected. Stool samples and rectal swabs from children with CD without perianal disease and healthy children were included as comparison. Whole shotgun metagenomic sequencing was performed.

RESULTS

A total of 31 children [mean age 15.5 ± 3.5 years] with perianal CD were prospectively enrolled. The fistula-associated microbiome showed an increase in alpha diversity and alteration in the abundance of several taxa compared with the rectal- and faecal-associated microbiome with key taxa belonging to the Proteobacteria phylum. Genes conferring resistance to the clinically used antibiotic regimen ciprofloxacin and metronidazole were found in the three sample types. In comparison with children without the perianal phenotype [N = 36] and healthy controls [N = 41], the mucosally-associated microbiome of children with perianal CD harboured a reduced butyrogenic potential. Linear discriminant analysis identified key taxa distinguishing the rectal mucosally-associated microbiome of children with perianal CD from children without this phenotype.

CONCLUSIONS

The microbial community within CD-related anorectal fistula is compositionally and functionally unique. Taken together, these findings emphasise the need to better understand the ecosystem of the fistula milieu to guide development of novel microbiome-based strategies in this CD phenotype.

Dietary fiber-based regulation of bile salt hydrolase activity in the gut microbiota and its relevance to human disease

Complications of short bowel syndrome (SBS) include malabsorption and bacterial overgrowth, requiring prolonged dependence on parenteral nutrition (PN). We hypothesized that the intolerance of whole food in some SBS patients might be due to the effect of dietary fiber on the gut microbiome. Shotgun metagenomic sequencing and targeted metabolomics were performed using biospecimens collected from 55 children with SBS and a murine dietary fiber model. Bioinformatic analyses were performed on these datasets as well as from a healthy human dietary intervention study. Compared to healthy controls, the gut microbiota in SBS had lower diversity and increased Proteobacteria, a pattern most pronounced in children on PN and inversely correlated with whole food consumption. Whole food intake correlated with increased glycoside hydrolases (GH) and bile salt hydrolases (BSH) with reduced fecal conjugated bile acids suggesting that dietary fiber regulates BSH activity via GHs. Mechanistic evidence supporting this notion was generated via fecal and plasma bile acid profiling in a healthy human fiber-free dietary intervention study as well as in a dietary fiber mouse experiment. Gaussian mixture modeling of fecal bile acids was used to identify three clinically relevant SBS phenotypes. Dietary fiber is associated with bile acid deconjugation likely via an interaction between gut microbiota BSHs and GHs in the small intestine, which may lead to whole food intolerance in patients with SBS. This mechanism not only has potential utility in clinical phenotyping and targeted therapeutics in SBS based on bile acid metabolism but may have relevance to other intestinal disease states.

IgA deficiency destabilizes immunological homeostasis towards intestinal microbiota and increases the risk of systemic immune dysregulation

Mammals produce large quantities of mucosal and systemic antibodies that maintain the intestinal barrier, shape the intestinal microbiome and promote lifelong mutualism with commensal microbes. Here, we developed an integrated host-commensal approach combining microbial flow cytometry and 16S rRNA gene sequencing to define the population of microbes that induce mucosal and systemic antibodies with CyTOF analysis in pediatric selective Immunoglobulin A (IgA) deficient and household control siblings to determine the impacts of IgA deficiency on host cellular immune phenotype. In healthy controls, mucosal secretory IgA and IgM antibodies coat an overlapping subset of microbes, predominantly Firmicutes and Proteobacteria. Serum IgG antibodies target a similar consortium of fecal microbes, revealing connections between mucosal and systemic antibody networks. Furthermore, we find broad systemic immune dysregulation in a subset of children and mice lacking IgA, including enhanced IgG targeting of fecal microbiota, elevated levels of inflammatory and allergic cytokines and alterations in T cell activation state. Thus, IgA tunes systemic interactions between the host and commensal microbiota. Understanding how IgA affects baseline immune tone has implications for predicting and preventing autoimmune, inflammatory and allergic diseases, as well as providing improved prognostic guidance to patients with IgA deficiency.

Supported by CHOP Microbiome Pilot Grant K08AI135091 Burroughs Wellcome Fund, the American Academy of Allergy, Asthma, and Immunology, the Immune Deficiency Foundation, the Primary Immune Deficiency Treatment Consortium and Chan Zuckerberg Initiative

The impact of environmental pH on the gut microbiota community structure and short chain fatty acid production

Environmental pH is a critical parameter for maintenance of the gut microbiota. Here, the impact of pH on the gut microbiota luminal and mucosal community structure and short chain fatty acid (SCFA) production was evaluated in vitro, and data compiled to reveal a donor-independent response to an increase or decrease in environmental pH. The results found that raising environmental pH significantly increased luminal community richness and decreased mucosal community evenness. This corresponded with an increased abundance of Ruminococcaceae Ruminococcus, and Erysipelotrichaceae Erysipelatoclostridium, and a decreased abundance of Coriobacteriaceae Collinsella, and Enterobacteriaceae Shigella for both the luminal and mucosal communities. Total SCFA levels were significantly higher, primarily due to an increase in acetic and 2-methylbutanoic acids. Lowering pH decreased luminal community evenness and decreased mucosal community evenness and richness. This corresponded with an increased abundance of Lachnospiraceae Enterocloster, Veillonellaceae Megasphaera, Veillonellaceae Sporomusa, Erysipelotrichaceae Eubacterium, and Alcaligenaceae Sutterella, and decreased abundance of Odoribacteraceae Butyricimonas, Fusobacteriaceae Fusobacterium, Veillonellaceae Phascolarctobacterium, and multiple Enterobacteriaceae species for both the luminal and mucosal communities. Total SCFA levels were significantly lower, with an observed drop in acetic and propionic acids, and increased butyric and valeric acids. Taken together, these results indicate that alterations to environmental pH can modulate the gut microbiota community structure and function, and some changes may occur in a donor-independent manner.

Early stool microbiome and metabolome signatures in pediatric patients undergoing allogeneic hematopoietic cell transplantation

BACKGROUND

The contribution of the gastrointestinal tract microbiome to outcomes after allogeneic hematopoietic cell transplantation (HCT) is increasingly recognized. Investigations of larger pediatric cohorts aimed at defining the microbiome state and associated metabolic patterns pretransplant are needed.

METHODS

We sought to describe the pretransplant stool microbiome in pediatric allogenic HCT patients at four centers. We performed shotgun metagenomic sequencing and untargeted metabolic profiling on pretransplant stool samples. Samples were compared with normal age-matched controls and by clinical characteristics. We then explored associations between stool microbiome measurements and metabolite concentrations.

RESULTS

We profiled stool samples from 88 pediatric allogeneic HCT patients, a median of 4 days before transplant. Pretransplant stool samples differed from healthy controls based on indices of alpha diversity and in the proportional abundance of specific taxa and bacterial genes. Relative to stool from healthy patients, samples from HCT patients had decreased proportion of Bacteroides, Ruminococcaeae, and genes involved in butyrate production, but were enriched for gammaproteobacterial species. No systematic differences in stool microbiome or metabolomic profiles by age, transplant indication, or hospital were noted. Stool metabolites demonstrated strong correlations with microbiome composition.

DISCUSSION

Stool samples from pediatric allogeneic HCT patients demonstrate substantial dysbiosis early in the transplant course. As microbiome disruptions associate with adverse transplant outcomes, pediatric-specific analyses examining longitudinal microbiome and metabolome changes are imperative to identify causal associations and to inform rational design of interventions.

Signatures of COVID-19 Severity and Immune Response in the Respiratory Tract Microbiome

Viral infection of the respiratory tract can be associated with propagating effects on the airway microbiome, and microbiome dysbiosis may influence viral disease. Here, we investigated the respiratory tract microbiome in coronavirus disease 2019 (COVID-19) and its relationship to disease severity, systemic immunologic features, and outcomes. We examined 507 oropharyngeal, nasopharyngeal, and endotracheal samples from 83 hospitalized COVID-19 patients as well as non-COVID patients and healthy controls. Bacterial communities were interrogated using 16S rRNA gene sequencing, and the commensal DNA viruses Anelloviridae and Redondoviridae were quantified by qPCR. We found that COVID-19 patients had upper respiratory microbiome dysbiosis and greater change over time than critically ill patients without COVID-19. Oropharyngeal microbiome diversity at the first time point correlated inversely with disease severity during hospitalization. Microbiome composition was also associated with systemic immune parameters in blood, as measured by lymphocyte/neutrophil ratios and immune profiling of peripheral blood mononuclear cells. Intubated patients showed patient-specific lung microbiome communities that were frequently highly dynamic, with prominence of Staphylococcus. Anelloviridae and Redondoviridae showed more frequent colonization and higher titers in severe disease. Machine learning analysis demonstrated that integrated features of the microbiome at early sampling points had high power to discriminate ultimate level of COVID-19 severity. Thus, the respiratory tract microbiome and commensal viruses are disturbed in COVID-19 and correlate with systemic immune parameters, and early microbiome features discriminate disease severity. Future studies should address clinical consequences of airway dysbiosis in COVID-19, its possible use as biomarkers, and the role of bacterial and viral taxa identified here in COVID-19 pathogenesis. IMPORTANCE COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection of the respiratory tract, results in highly variable outcomes ranging from minimal illness to death, but the reasons for this are not well understood. We investigated the respiratory tract bacterial microbiome and small commensal DNA viruses in hospitalized COVID-19 patients and found that each was markedly abnormal compared to that in healthy people and differed from that in critically ill patients without COVID-19. Early airway samples tracked with the level of COVID-19 illness reached during hospitalization, and the airway microbiome also correlated with immune parameters in blood. These findings raise questions about the mechanisms linking SARS-CoV-2 infection and other microbial inhabitants of the airway, including whether the microbiome might regulate severity of COVID-19 disease and/or whether early microbiome features might serve as biomarkers to discriminate disease severity.

Gut Microbiome Changes Associated with Epithelial Barrier Damage and Systemic Inflammation during Antiretroviral Therapy of Chronic SIV Infection

Gut dysbiosis is a common feature associated with the chronic inflammation of HIV infection. Toward understanding the interplay of chronic treated HIV infection, dysbiosis, and systemic inflammation, we investigated longitudinal fecal microbiome changes and plasma inflammatory markers in the nonhuman primate model. Following simian immunodeficiency virus (SIV) infection in rhesus macaques, significant changes were observed in several members of the phylum Firmicutes along with an increase in Bacteroidetes. Viral suppression with antiretroviral therapy (ART) resulted in an early but partial recovery of compositional changes and butyrate producing genes in the gut microbiome. Over the course of chronic SIV infection and long-term ART, however, the specific loss of Faecalibacterium prausnitzii and Treponema succinifaciens significantly correlated with an increase in plasma inflammatory cytokines including IL-6, G-CSF, I-TAC, and MIG. Further, the loss of T. succinifaciens correlated with an increase in circulating biomarkers of gut epithelial barrier damage (IFABP) and microbial translocation (LBP and sCD14). As F. prausnitzii and T. succinifaciens are major short-chain fatty acid producing bacteria, their sustained loss during chronic SV-ART may contribute to gut inflammation and metabolic alterations despite effective long-term control of viremia. A better understanding of the correlations between the anti-inflammatory bacterial community and healthy gut barrier functions in the setting of long-term ART may have a major impact on the clinical management of inflammatory comorbidities in HIV-infected individuals.

Signatures of COVID-19 severity and immune response in the respiratory tract microbiome

Rationale

Viral infection of the respiratory tract can be associated with propagating effects on the airway microbiome, and microbiome dysbiosis may influence viral disease.

Objective

To define the respiratory tract microbiome in COVID-19 and relationship disease severity, systemic immunologic features, and outcomes.

Methods and Measurements

We examined 507 oropharyngeal, nasopharyngeal and endotracheal samples from 83 hospitalized COVID-19 patients, along with non-COVID patients and healthy controls. Bacterial communities were interrogated using 16S rRNA gene sequencing, commensal DNA viruses Anelloviridae and Redondoviridae were quantified by qPCR, and immune features were characterized by lymphocyte/neutrophil (L/N) ratios and deep immune profiling of peripheral blood mononuclear cells (PBMC).

Main Results

COVID-19 patients had upper respiratory microbiome dysbiosis, and greater change over time than critically ill patients without COVID-19. Diversity at the first time point correlated inversely with disease severity during hospitalization, and microbiome composition was associated with L/N ratios and PBMC profiles in blood. Intubated patients showed patient-specific and dynamic lung microbiome communities, with prominence of Staphylococcus. Anelloviridae and Redondoviridae showed more frequent colonization and higher titers in severe disease. Machine learning analysis demonstrated that integrated features of the microbiome at early sampling points had high power to discriminate ultimate level of COVID-19 severity.

Conclusions

The respiratory tract microbiome and commensal virome are disturbed in COVID-19, correlate with systemic immune parameters, and early microbiome features discriminate disease severity. Future studies should address clinical consequences of airway dysbiosis in COVID-19, possible use as biomarkers, and role of bacterial and viral taxa identified here in COVID-19 pathogenesis.

Metabolic Analysis of Regionally Distinct Gut Microbial Communities Using an In Vitro Platform

The colon gut microbiota is responsible for complex chemical conversions of nutrients and subsequent release of metabolites that have diverse biological consequences. However, information on the metabolic dynamics that occur longitudinally through the colon is limited. Here, gas and liquid chromatographies coupled with mass spectrometry were applied to generate metabolic profiles of the region-specific microbial communities cultured using an in vitro platform simulating the ascending (AC), transverse (TC), and descending (DC) colon regions. Comparative analysis revealed a large divergence between metabolic profiles of the AC and the TC and DC regions in terms of short-chain fatty acid production, metabolic spectrum, and conversion of bile acids. Metagenomic evaluation revealed that the regionally derived metabolic profiles had strong correlation to community composition and genetic potential. Together, the results provide key insights regarding the metabolic divergence of the regional communities that are integral to understand the structure-function relationship of the gut microbiota.

Permissive microbiome characterizes human subjects with a neurovascular disease cavernous angioma

Cavernous angiomas (CA) are common vascular anomalies causing brain hemorrhage. Based on mouse studies, roles of gram-negative bacteria and altered intestinal homeostasis have been implicated in CA pathogenesis, and pilot study had suggested potential microbiome differences between non-CA and CA individuals based on 16S rRNA gene sequencing. We here assess microbiome differences in a larger cohort of human subjects with and without CA, and among subjects with different clinical features, and conduct more definitive microbial analyses using metagenomic shotgun sequencing. Relative abundance of distinct bacterial species in CA patients is shown, consistent with postulated permissive microbiome driving CA lesion genesis via lipopolysaccharide signaling, in humans as in mice. Other microbiome differences are related to CA clinical behavior. Weighted combinations of microbiome signatures and plasma inflammatory biomarkers enhance associations with disease severity and hemorrhage. This is the first demonstration of a sensitive and specific diagnostic microbiome in a human neurovascular disease.

Lifestyle and the presence of helminths is associated with gut microbiome composition in Cameroonians

BACKGROUND

African populations provide a unique opportunity to interrogate host-microbe co-evolution and its impact on adaptive phenotypes due to their genomic, phenotypic, and cultural diversity. We integrate gut microbiome 16S rRNA amplicon and shotgun metagenomic sequence data with quantification of pathogen burden and measures of immune parameters for 575 ethnically diverse Africans from Cameroon. Subjects followed pastoralist, agropastoralist, and hunter-gatherer lifestyles and were compared to an urban US population from Philadelphia.

RESULTS

We observe significant differences in gut microbiome composition across populations that correlate with subsistence strategy and country. After these, the variable most strongly associated with gut microbiome structure in Cameroonians is the presence of gut parasites. Hunter-gatherers have high frequencies of parasites relative to agropastoralists and pastoralists. Ascaris lumbricoides, Necator americanus, Trichuris trichiura, and Strongyloides stercoralis soil-transmitted helminths ("ANTS" parasites) significantly co-occur, and increased frequency of gut parasites correlates with increased gut microbial diversity. Gut microbiome composition predicts ANTS positivity with 80% accuracy. Colonization with ANTS, in turn, is associated with elevated levels of TH1, TH2, and proinflammatory cytokines, indicating an association with multiple immune mechanisms. The unprecedented size of this dataset allowed interrogation of additional questions-for example, we find that Fulani pastoralists, who consume high levels of milk, possess an enrichment of gut bacteria that catabolize galactose, an end product of lactose metabolism, and of bacteria that metabolize lipids.

CONCLUSIONS

These data document associations of bacterial microbiota and eukaryotic parasites with each other and with host immune responses; each of these is further correlated with subsistence practices.

Abstract IA25: Tumors alter gut microbiota to suppress immunity and foster progression

Immune dysfunction is commonly observed in patients with cancer contributing to tumor progression. While previous work established a connection between the gut microbiota and the immune system, the mechanisms by which microbiotas contribute to cancer-associated immune dysfunction are not well understood. Using multiple mouse cancer models, we demonstrated robust alterations of gut microbiota in tumor-bearing mice and a substantial change in antimicrobial peptides produced by the gut epithelium. We identified an overall reduction in IFN-γ T cells in tumor-bearing mice, which was rescued with antibiotics treatment or by co-housing tumor-bearing mice with healthy mice. Similar to mouse, we observed changes in gut microbiota and antimicrobial peptides levels of patients diagnosed with ovarian or lung cancer. We identify Firmicutes Ruminococcus members as key promoters of immune dysfunctions and tumor development. These findings identify a new mechanism of immune modulation utilized by tumors to undermine the immune responses and promote tumor progression.

Citation Format: Mireia Hribe-Herranz, Kyle Bittinger, Ceylan Tanes, Stavros Rafail, Stefano Pierini, Edgar Ben-Joseph, Janos Tanyi, Andrea Facciabene. Tumors alter gut microbiota to suppress immunity and foster progression [abstract]. In: Proceedings of the AACR Special Conference on the Microbiome, Viruses, and Cancer; 2020 Feb 21-24; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2020;80(8 Suppl):Abstract nr IA25.

Distinct cellular roles for PDCD10 define a gut-brain axis in cerebral cavernous malformation

Cerebral cavernous malformation (CCM) is a genetic, cerebrovascular disease. Familial CCM is caused by genetic mutations in KRIT1, CCM2, or PDCD10 Disease onset is earlier and more severe in individuals with PDCD10 mutations. Recent studies have shown that lesions arise from excess mitogen-activated protein kinase kinase kinase 3 (MEKK3) signaling downstream of Toll-like receptor 4 (TLR4) stimulation by lipopolysaccharide derived from the gut microbiome. These findings suggest a gut-brain CCM disease axis but fail to define it or explain the poor prognosis of patients with PDCD10 mutations. Here, we demonstrate that the gut barrier is a primary determinant of CCM disease course, independent of microbiome configuration, that explains the increased severity of CCM disease associated with PDCD10 deficiency. Chemical disruption of the gut barrier with dextran sulfate sodium augments CCM formation in a mouse model, as does genetic loss of Pdcd10, but not Krit1, in gut epithelial cells. Loss of gut epithelial Pdcd10 results in disruption of the colonic mucosal barrier. Accordingly, loss of Mucin-2 or exposure to dietary emulsifiers that reduce the mucus barrier increases CCM burden analogous to loss of Pdcd10 in the gut epithelium. Last, we show that treatment with dexamethasone potently inhibits CCM formation in mice because of the combined effect of action at both brain endothelial cells and gut epithelial cells. These studies define a gut-brain disease axis in an experimental model of CCM in which a single gene is required for two critical components: gut epithelial function and brain endothelial signaling.

Metagenomic assessment of the Cebus apella gut microbiota

Cebus Apella (C. apella) is a species of Nonhuman Primate (NHP) used for biomedical research because it is phylogenetically similar and shares anatomical commonalities with humans. Here, the gut microbiota of three C. apella were examined in the different regions of the intestinal tract. Using metagenomics, the gut microbiota associated with the luminal content and mucus layer for each intestinal region was identified, and functionality was investigated by quantifying the levels of short chain fatty acids (SCFAs) produced. The results of this study show a high degree of similarity in the intestinal communities among C. apella subjects, with multiple shared characteristics. First, the communities in the lumen were more phylogenetically diverse and rich compared to the mucus layer communities throughout the entire intestinal tract. The small intestine communities in the lumen displayed a higher Shannon diversity index compared to the colon communities. Second, all the communities were dominated by aero-tolerant taxa such as Streptococcus, Enterococcus, Abiotrophia, and Lactobacillus, although there was preferential colonization of specific taxa observed. Finally, the primary SCFA produced throughout the intestinal tract was acetic acid, with some propionic acid and butyric acid detected in the colon regions. The small intestine microbiota produced significantly less SCFAs compared to the communities in the colon. Collectively, these data provide an in-depth report on the composition, distribution, and SCFA production of the gut microbiota along the intestinal tract of the C. apella NHP animal model.

Antigen-presenting ILC3 regulate T cell-dependent IgA responses to colonic mucosal bacteria

Intestinal immune homeostasis is dependent upon tightly regulated and dynamic host interactions with the commensal microbiota. Immunoglobulin A (IgA) produced by mucosal B cells dictates the composition of commensal bacteria residing within the intestine. While emerging evidence suggests the majority of IgA is produced innately and may be polyreactive, mucosal-dwelling species can also elicit IgA via T cell-dependent mechanisms. However, the mechanisms that modulate the magnitude and quality of T cell-dependent IgA responses remain incompletely understood. Here we demonstrate that group 3 innate lymphoid cells (ILC3) regulate steady state interactions between T follicular helper cells (TfH) and B cells to limit mucosal IgA responses. ILC3 used conserved migratory cues to establish residence within the interfollicular regions of the intestinal draining lymph nodes, where they act to limit TfH responses and B cell class switching through antigen presentation. The absence of ILC3-intrinsic antigen presentation resulted in increased and selective IgA coating of bacteria residing within the colonic mucosa. Together these findings implicate lymph node resident, antigen-presenting ILC3 as a critical regulatory checkpoint in the generation of T cell-dependent colonic IgA and suggest ILC3 act to maintain tissue homeostasis and mutualism with the mucosal-dwelling commensal microbiota.

Applying Advanced In Vitro Culturing Technology to Study the Human Gut Microbiota

The human gut microbiota plays a vital role in both human health and disease. Studying the gut microbiota using an in vivo model, is difficult due to its complex nature, and its diverse association with mammalian components. The goal of this protocol is to culture the gut microbiota in vitro, which allows for the study of the gut microbiota dynamics, without having to consider the contribution of the mammalian milieu. Using in vitro culturing technology, the physiological conditions of the gastro intestinal tract are simulated, including parameters such as pH, temperature, anaerobiosis, and transit time. The intestinal surface of the colon is simulated by adding mucin-coated carriers, creating a mucosal phase, and adding further dimension. The gut microbiota is introduced by inoculating with the human fecal material. Upon inoculation with this complex mixture of bacteria, specific microbes are enriched in the different longitudinal (ascending, transverse and descending colons) and transversal (luminal and mucosal) environments of the in vitro model. It is crucial to allow the system to reach a steady state, in which the community and the metabolites produced remain stable. The experimental results in this manuscript demonstrate how the inoculated gut microbiota community develops into a stable community over time. Once steady state is achieved, the system can be used to analyze bacterial interactions and community functions or to test the effects of any additives on the gut microbiota, such as food, food components, or pharmaceuticals.

Childhood adversity impact on gut microbiota and inflammatory response to stress during pregnancy

BACKGROUND

Adverse childhood experiences (ACEs), such as abuse or chronic stress, program an exaggerated adult inflammatory response to stress. Emerging rodent research suggests that the gut microbiome may be a key mediator in the association between early life stress and dysregulated glucocorticoid-immune response. However, ACE impact on inflammatory response to stress, or on the gut microbiome, have not been studied in human pregnancy, when inflammation increases risk of poor outcomes. The aim of this study was to assess the relationships among ACE, the gut microbiome, and cytokine response to stress in pregnant women.

METHODS

Physically and psychiatrically healthy adult pregnant women completed the Adverse Childhood Experiences Questionnaire (ACE-Q) and gave a single stool sample between 20 and 26 weeks gestation. Stool DNA was isolated and 16S sequencing was performed. Three 24-hour food recalls were administered to assess dietary nutrient intake. A subset of women completed the Trier Social Stress Test (TSST) at 22-34 weeks gestation; plasma interleukin-6 (IL-6), interleukin-1β (IL-1β), high sensitivity C-reactive protein (hsCRP), tumor necrosis factor α (TNF-α), and cortisol were measured at four timepoints pre and post stressor, and area under the curve (AUC) was calculated.

RESULTS

Forty-eight women completed the ACE-Q and provided stool; 19 women completed the TSST. Women reporting 2 or more ACEs (high ACE) had greater differential abundance of gut Prevotella than low ACE participants (q = 5.7 × 10^-13). Abundance of several gut taxa were significantly associated with cortisol, IL-6, TNF-α and CRP AUCs regardless of ACE status. IL-6 response to stress was buffered among high ACE women with high intake of docosahexaenoic acid (DHA) (p = 0.03) and eicosapentaenoic acid (EPA) (p = 0.05).

DISCUSSION

Our findings suggest that multiple childhood adversities are associated with changes in gut microbiota composition during pregnancy, and such changes may contribute to altered inflammatory and glucocorticoid response to stress. While preliminary, this is the first study to demonstrate an association between gut microbiota and acute glucocorticoid-immune response to stress in a clinical sample. Finally, exploratory analyses suggested that high ACE women with high dietary intake of ω-3 polyunsaturated fatty acids (PUFAs) had a dampened inflammatory response to acute stress, suggesting potentially protective effects of ω-3s in this high-risk population. Given the adverse effects of inflammation on pregnancy and the developing fetus, mechanisms by which childhood adversity influence the gut-brain axis and potential protective factors such as diet should be further explored.

Establishing a mucosal gut microbial community in vitro using an artificial simulator

The Twin Simulator of the Human Intestinal Microbial Ecosystem (TWINSHIME^®) was initially developed to study the luminal gut microbiota of the ascending (AC), transverse (TC), and descending (DC) colon regions. Given the unique composition and potential importance of the mucosal microbiota for human health, the TWINSHIME was recently adapted to simulate the mucosal microbiota as well as the luminal community. It has been previously demonstrated that the luminal community in the TWINSHIME reaches a steady state within two weeks post inoculation, and is able to differentiate into region specific communities. However, less is known regarding the mucosal community structure and dynamics. During the current study, the luminal and mucosal communities in each region of the TWINSHIME were evaluated over the course of six weeks. Based on 16S rRNA gene sequencing and short chain fatty acid analysis, it was determined that both the luminal and mucosal communities reached stability 10–20 days after inoculation, and remained stable until the end of the experiment. Bioinformatics analysis revealed the formation of unique community structures between the mucosal and luminal phases in all three colon regions, yet these communities were similar to the inoculum. Specific colonizers of the mucus mainly belonged to the Firmicutes phylum and included Lachnospiraceae (AC/TC/DC), Ruminococcaceae and Eubacteriaceae (AC), Lactobacillaceae (AC/TC), Clostridiaceae and Erysipelotrichaceae (TC/DC). In contrast, Bacteroidaceae were enriched in the gut lumen of all three colon regions. The unique profile of short chain fatty acid (SCFA) production further demonstrated system stability, but also proved to be an area of marked differences between the in vitro system and in vivo reports. Results of this study demonstrate that it is possible to replicate the community structure and composition of the gut microbiota in vitro. Through implementation of this system, the human gut microbiota can be studied in a dynamic and continuous fashion.

Abstract 3798: Gut microbiota modulates adoptive cell therapy via CD8α dendritic cells

Adoptive T-Cell therapy (ACT) is a promising new modality for malignancies. Here, we report that adoptive T-cell efficacy in tumor-bearing mice is significantly affected by differences in the native composition of the gut microbiome, treatment with antibiotics or by heterologous fecal transfer. Depletion of bacteria with vancomycin, decreased the rate of tumor growth in mice receiving ACT, whereas treatment with neomycin and metronidazole had no effect, indicating the role of specific bacteria in host response. Vancomycin treatment induced an increase in systemic CD8α+ dendritic cells, which mediated a sustained systemic expansion of adoptively transferred antitumor T cells in an IL-12-dependent manner. In subjects undergoing allogeneic hematopoietic cell transplantation, we found that oral vancomycin also increased IL-12 levels. Collectively, our findings demonstrate an important role played by the gut microbiota in the antitumor effectiveness of ACT and suggest new avenues to improve response to ACT by altering the gut microbiota.

Citation Format: Mireia Uribe-Herranz, Kyle Bittinger, Stavros Rafail, Sonia Guedan, Stefano Pierini, Ceylan Tanes, Saar A. Gill, Janos Tany, Mark A. Morgan, Frederic D. Bushman, Carl H. June, Andrea Facciabene. Gut microbiota modulates adoptive cell therapy via CD8α dendritic cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3798.

Gut microbiota modulates adoptive cell therapy via CD8α dendritic cells and IL-12

Adoptive T cell therapy (ACT) is a promising new modality for malignancies. Here, we report that adoptive T cell efficacy in tumor-bearing mice is significantly affected by differences in the native composition of the gut microbiome or treatment with antibiotics, or by heterologous fecal transfer. Depletion of bacteria with vancomycin decreased the rate of tumor growth in mice from The Jackson Laboratory receiving ACT, whereas treatment with neomycin and metronidazole had no effect, indicating the role of specific bacteria in host response. Vancomycin treatment induced an increase in systemic CD8α+ DCs, which sustained systemic adoptively transferred antitumor T cells in an IL-12-dependent manner. In subjects undergoing allogeneic hematopoietic cell transplantation, we found that oral vancomycin also increased IL-12 levels. Collectively, our findings demonstrate an important role played by the gut microbiota in the antitumor effectiveness of ACT and suggest potentially new avenues to improve response to ACT by altering the gut microbiota.

Endothelial TLR4 and the microbiome drive cerebral cavernous malformations

Cerebral cavernous malformations (CCMs) are a cause of stroke and seizure for which no effective medical therapies yet exist. CCMs arise from the loss of an adaptor complex that negatively regulates MEKK3-KLF2/4 signalling in brain endothelial cells, but upstream activators of this disease pathway have yet to be identified. Here we identify endothelial Toll-like receptor 4 (TLR4) and the gut microbiome as critical stimulants of CCM formation. Activation of TLR4 by Gram-negative bacteria or lipopolysaccharide accelerates CCM formation, and genetic or pharmacologic blockade of TLR4 signalling prevents CCM formation in mice. Polymorphisms that increase expression of the TLR4 gene or the gene encoding its co-receptor CD14 are associated with higher CCM lesion burden in humans. Germ-free mice are protected from CCM formation, and a single course of antibiotics permanently alters CCM susceptibility in mice. These studies identify unexpected roles for the microbiome and innate immune signalling in the pathogenesis of a cerebrovascular disease, as well as strategies for its treatment.

Optimizing methods and dodging pitfalls in microbiome research

Research on the human microbiome has yielded numerous insights into health and disease, but also has resulted in a wealth of experimental artifacts. Here, we present suggestions for optimizing experimental design and avoiding known pitfalls, organized in the typical order in which studies are carried out. We first review best practices in experimental design and introduce common confounders such as age, diet, antibiotic use, pet ownership, longitudinal instability, and microbial sharing during cohousing in animal studies. Typically, samples will need to be stored, so we provide data on best practices for several sample types. We then discuss design and analysis of positive and negative controls, which should always be run with experimental samples. We introduce a convenient set of non-biological DNA sequences that can be useful as positive controls for high-volume analysis. Careful analysis of negative and positive controls is particularly important in studies of samples with low microbial biomass, where contamination can comprise most or all of a sample. Lastly, we summarize approaches to enhancing experimental robustness by careful control of multiple comparisons and to comparing discovery and validation cohorts. We hope the experimental tactics summarized here will help researchers in this exciting field advance their studies efficiently while avoiding errors.

Dachshund binds p53 to block the growth of lung adenocarcinoma cells

Hyperactive EGF receptor (EGFR) and mutant p53 are common genetic abnormalities driving the progression of non-small cell lung cancer (NSCLC), the leading cause of cancer deaths in the world. The Drosophila gene Dachshund (Dac) was originally cloned as an inhibitor of hyperactive EGFR alleles. Given the importance of EGFR signaling in lung cancer etiology, we examined the role of DACH1 expression in lung cancer development. DACH1 protein and mRNA expression was reduced in human NSCLC. Reexpression of DACH1 reduced NSCLC colony formation and tumor growth in vivo via p53. Endogenous DACH1 colocalized with p53 in a nuclear, extranucleolar location, and shared occupancy of -15% of p53-bound genes in ChIP sequencing. The C-terminus of DACH1 was necessary for direct p53 binding, contributing to the inhibition of colony formation and cell-cycle arrest. Expression of the stem cell factor SOX2 was repressed by DACH1, and SOX2 expression was inversely correlated with DACH1 in NSCLC. We conclude that DACH1 binds p53 to inhibit NSCLC cellular growth.