The microbiota in inflammatory bowel disease: friend, bystander, and sometime-villain

A guide to germ-free and gnotobiotic mouse technology to study health and disease

The intestinal microbiota has major influence on human physiology and modulates health and disease. Complex host-microbe interactions regulate various homeostatic processes, including metabolism and immune function, while disturbances in microbiota composition (dysbiosis) are associated with a plethora of human diseases and are believed to modulate disease initiation, progression and therapy response. The vast complexity of the human microbiota and its metabolic output represents a great challenge in unraveling the molecular basis of host-microbe interactions in specific physiological contexts. To increase our understanding of these interactions, functional microbiota research using animal models in a reductionistic setting are essential. In the dynamic landscape of gut microbiota research, the use of germ-free and gnotobiotic mouse technology, in which causal disease-driving mechanisms can be dissected, represents a pivotal investigative tool for functional microbiota research in health and disease, in which causal disease-driving mechanisms can be dissected. A better understanding of the health-modulating functions of the microbiota opens perspectives for improved therapies in many diseases. In this review, we discuss practical considerations for the design and execution of germ-free and gnotobiotic experiments, including considerations around germ-free rederivation and housing conditions, route and timing of microbial administration, and dosing protocols. This comprehensive overview aims to provide researchers with valuable insights for improved experimental design in the field of functional microbiota research.

Inflammatory bowel disease in the elderly: A focus on disease characteristics and treatment patterns

Background

As the population ages, the number of elderly inflammatory bowel disease (IBD) patients is expected to increase. The clinical features and therapeutic options for young and old patients may differ, as elderly IBD patients are likely to have different comorbidities and disease characteristics. The goal of this study was to examine the clinical aspects and therapeutic choices for elderly Saudi IBD patients.

Methods

We conducted a retrospective study aimed at describing the demographic, clinical, and management characteristics of IBD in elderly patients (≥60 years) who followed up at King Abdulaziz University Hospital (KAUH), Jeddah, Saudi Arabia. The data was extracted from the KAUH inflammatory bowel disease information system (IBDIS) registry. The primary outcome was to describe disease characteristics in accordance with the Montréal classification and the secondary outcomes were to describe treatment patterns and identify significant clinical associations.

Results

Our data were collected from 76 patients who fulfilled the study inclusion criteria. Females outnumbered males (53.9% vs 46.1%) and the mean age was 51.5 ± 9.7 years. Essential hypertension (26.3%) was the most common comorbidity followed by diabetes mellitus (23.6%), and malignant neoplasms (9.21%). More than half of the patients with Crohn's disease (CD) had disease onset after forty years of age. The most common form of disease distribution was ileocolonic disease (64.7%). Less than 17% of patients had a penetrating disease phenotype. About 88 percent of patients with UC presented >40 years of age. Approximately, half of the cohort had left-sided ulcerative colitis (UC) (48%), followed by pancolitis (40%). The most prescribed medication class for IBD was 5-aminosalicylic acid (5-ASA) derivatives (56.58%) followed by corticosteroids and immunosuppressive drugs.

Conclusions

In Saudi Arabia, age-specific concerns including comorbidities and polypharmacy remain the major challenges in the management of elderly IBD patients.

How Do Microorganisms Influence the Development of Endometriosis? Participation of Genital, Intestinal and Oral Microbiota in Metabolic Regulation and Immunopathogenesis of Endometriosis

Microorganisms inhabiting the human body play an extremely key role in its proper functioning, as well as in the development of the immune system, which, by maintaining the immune balance, allows you to enjoy health. Dysbiosis of the intestinal microbiota, or in the oral cavity or reproductive tract, understood as a change in the number and diversity of all microorganisms inhabiting them, may correlate with the development of many diseases, including endometriosis, as researchers have emphasized. Endometriosis is an inflammatory, estrogen-dependent gynecological condition defined by the growth of endometrial cells outside the uterine cavity. Deregulation of immune homeostasis resulting from microbiological disorders may generate chronic inflammation, thus creating an environment conducive to the increased adhesion and angiogenesis involved in the development of endometriosis. In addition, research in recent years has implicated bacterial contamination and immune activation, reduced gastrointestinal function by cytokines, altered estrogen metabolism and signaling, and abnormal progenitor and stem cell homeostasis, in the pathogenesis of endometriosis. The aim of this review was to present the influence of intestinal, oral and genital microbiota dysbiosis in the metabolic regulation and immunopathogenesis of endometriosis.

Review article: bugs, inflammation and mood-a microbiota-based approach to psychiatric symptoms in inflammatory bowel diseases

BACKGROUND

Psychiatric co-morbidities including depression and anxiety are common in inflammatory bowel diseases (IBD). Emerging evidence suggests that interactions between the gut microbiota and brain may play a role in the pathogenesis of psychiatric symptoms in IBD.

AIM

To review the literature on microbiota-brain-gut interactions in gut inflammation, psychosocial stress and mental disorders and to discuss the putative mediating role of gut microbiota in the development of psychiatric symptoms or co-morbidities in IBD.

METHODS

A literature search was conducted on Ovid and Pubmed to select relevant animal and human studies reporting an association between IBD, mental disorders and gut microbiota.

RESULTS

Gut microbial alterations are frequently reported in subjects with IBD and with mental disorders. Both have been associated with reduced faecal bacterial diversity, decreased taxa within the phylum Firmicutes and increased Gammaproteobacteria. In animal studies, microbial perturbations induce behavioural changes and modulate inflammation in mice. Anxiety- and depression-like behaviours in animals can be transferred via faecal microbiota. In humans, modulation of the gut microbiota with probiotics is associated with behavioural and mood changes. Recent data show correlations in changes of faecal and mucosal microbiota and psychological distress in patients with IBD independent of disease activity.

CONCLUSION

Both IBD and mental disorders are associated with gut microbial alterations. Preclinical and preliminary human studies have shown a mediating role of the gut microbiota in intestinal inflammation and anxiety, depression and stress. Targeting the gut microbiota may represent a useful therapeutic approach for the treatment of psychiatric co-morbidities in IBD.

The Interaction of the Gut Microbiota with the Mucus Barrier in Health and Disease in Human

Glycoproteins are major players in the mucus protective barrier in the gastrointestinal and other mucosal surfaces. In particular the mucus glycoproteins, or mucins, are responsible for the protective gel barrier. They are characterized by their high carbohydrate content, present in their variable number, tandem repeat domains. Throughout evolution the mucins have been maintained as integral components of the mucosal barrier, emphasizing their essential biological status. The glycosylation of the mucins is achieved through a series of biosynthetic pathways processes, which generate the wide range of glycans found in these molecules. Thus mucins are decorated with molecules having information in the form of a glycocode. The enteric microbiota interacts with the mucosal mucus barrier in a variety of ways in order to fulfill its many normal processes. How bacteria read the glycocode and link to normal and pathological processes is outlined in the review.

Gut bacteria are required for the benefits of black raspberries in Apc Min/+ mice

BACKGROUND

The gut microbiota plays a pivotal role in the development of inflammatory bowel disease and colorectal cancer.

OBJECTIVE

To determine whether the gut microbiota is required for the chemoprotective effects of black raspberries (BRBs) in Apc ^Min/+ mice.

METHODS

Apc ^Min/+ mice were given (a) a control diet for 8 weeks, or (b) the control diet for 4 weeks and then a 5% BRB diet for additional 4 weeks, or (c) the control diet and antibiotics for 4 weeks followed by the 5% BRB diet and antibiotics for the next 4 weeks. At the end of the study, all the mice were euthanized, and colonic and intestinal polyps were counted. mRNA expression levels of TLR4, NF-κB1, and COX2 were determined in colon and small intestine of these Apc ^Min/+ mice by quantitative real-time PCR.

RESULTS

5% BRBs significantly suppressed intestinal and colonic polyp development in the Apc ^Min/+ mice, whereas antibiotics significantly abolished BRBs' chemoprotective effects. BRBs decreased mRNA levels of TLR4, NF-κB1, and COX2 in colon, whereas significantly enhanced mRNA levels of TLR4 and NF-κB1 were observed in small intestine of BRB-treated Apc ^Min/+ mice fed antibiotics.

CONCLUSIONS

The gut microbiota is required for BRBs' chemoprotection against polyp development in Apc ^Min/+ mice.

Associations between Folate and Vitamin B12 Levels and Inflammatory Bowel Disease: A Meta-Analysis

Background: Inflammatory bowel disease (IBD) patients may be at risk of vitamin B12 and folate insufficiencies, as these micronutrients are absorbed in the small intestine, which is affected by IBD. However, a consensus has not been reached on the association between IBD and serum folate and vitamin B12 concentrations. Methods: In this study, a comprehensive search of multiple databases was performed to identify studies focused on the association between IBD and serum folate and vitamin B12 concentrations. Studies that compared serum folate and vitamin B12 concentrations between IBD and control patients were selected for inclusion in the meta-analysis. Results: The main outcome was the mean difference in serum folate and vitamin B12 concentrations between IBD and control patients. Our findings indicated that the average serum folate concentration in IBD patients was significantly lower than that in control patients, whereas the mean serum vitamin B12 concentration did not differ between IBD patients and controls. In addition, the average serum folate concentration in patients with ulcerative colitis (UC) but not Crohn’s disease (CD) was significantly lower than that in controls. This meta-analysis identified a significant relationship between low serum folate concentration and IBD. Conclusions: Our findings suggest IBD may be linked with folate deficiency, although the results do not indicate causation. Thus, providing supplements of folate and vitamin B12 to IBD patients may improve their nutritional status and prevent other diseases.

Mild clinical behaviour of Crohn disease in elderly patients in a Latin American country: A case-control study

BACKGROUND

Crohn disease is characterized by fluctuating clinical behaviour, which is influenced by various factors. There are no data from Latin America that evaluate the clinical behaviour of Crohn disease in elderly patients.

OBJECTIVE

To evaluate the clinical course of elderly onset Crohn disease compared with younger onset in the Mexican population.

METHODS

The present analysis was a case-control study that included 132 patients with a histopathological diagnosis of Crohn disease between 1983 and 2013 in an inflammatory bowel disease clinic of a tertiary care centre. Statistical analysis was performed using SPSS version 17 (IBM Corporation, USA) and descriptive statistics, χ2 and Fisher's exact test for categorical variables and Student's t test for numerical variables. Univariate and multivariate analysis were performed to identify associated risk factors and OR was calculated.

RESULTS

A total of 132 patients (73 men and 59 women) were divided into two groups according to age at diagnosis: 27 cases (>60 years of age) and 105 controls (≤60 years of age). Factors influencing the clinical course of Crohn disease in the elderly were: female sex (OR 2.55 [95% CI 1.06 to 6.10]; P=0.02); colonic location (OR 0.22 [95% CI 0.03 to 0.89]; P=0.02); mild clinical behaviour of disease (OR 10.08 [95% CI 3.74 to 27.17]; P=0.0001); response to medical treatment (OR 2.85 [95% CI 1.08 to 7.48]; P=0.02); frequent use of sulfasalazine (OR 4.46 [95% CI 1.22 to 16.28]; P=0.03); less use of azathioprine (OR 0.38 [95% CI 0.13 to 1.03]; P=0.04); and long-term remission (OR 4.96 [95% CI 1.70 to 14.48]; P=0.002).

CONLCUSION

Elderly patients with Crohn disease had a mild clinical course characterized by the lack of escalation to immunosuppressive and anti-tumour necrosis factor therapy, as well as long-term remission.

Systematic review on intervention with prebiotics/probiotics in patients with obesity-related nonalcoholic fatty liver disease

BACKGROUND

The gut microbiota is modulated by metabolic derangements, such as nutrition overload and obesity.

AIM

The aim of this systematic review is to summarize the role of these gut modifiers in nonalcoholic fatty liver disease (NAFLD) and obesity.

METHODS

A systematic search of MEDLINE (from 1946), PubMed (from 1946) and EMBASE (from 1949) databases through May 2014 was carried out to identify relevant articles. The search terms were 'probiotic' AND 'NAFLD', 'prebiotic' AND 'NAFLD', 'antibiotic' AND 'NAFLD', 'probiotics' AND 'obesity', 'prebiotic' AND 'obesity' or 'antibiotic' AND 'obesity'; these terms were searched as text word in 'clinical trials' and as exploded medical subject headings where possible.

RESULTS

The evidence in the literature is scant, due to the scarcity of appropriately powered, randomized, controlled clinical trials, involving various centers and population of different origin.

CONCLUSION

Although probiotics and prebiotics have been proposed in the treatment and prevention of patients with obesity-related NAFLD, their therapeutic use is not supported by high-quality clinical studies.

Characterization of inflammatory bowel disease in elderly patients: A review of epidemiology, current practices and outcomes of current management strategies

The authors review and summarize the current literature regarding the epidemiology, clinical presentation and management of inflammatory bowel disease (IBD) in elderly patients. Among elderly patients, the incidence of ulcerative colitis (UC) is higher than that of Crohn disease (CD). Elderly patients with a new diagnosis of UC are more likely to be male and have left-sided colitis. Elderly patients with a new diagnosis of CD are more likely to be female and have colonic disease. Conversely, increasing age at diagnosis has been associated with a lower likelihood of having any of a family history of IBD, perianal disease in CD and extraintestinal manifestations. Although response to drug therapies appears to be similar in elderly patients and younger individuals, the elderly are more likely to receive 5-aminosalicylic acid agents, and less likely to receive immunomodulators and biologics. Corticosteroid use in the elderly is comparable with use in younger individuals. The rates of surgical intervention appear to be lower for elderly CD patients but not elderly UC patients. Elderly individuals with UC are more likely to need urgent colectomy, which is associated with an increased mortality rate. Elective surgery is associated with similar outcomes among the elderly and young patients with IBD. Therefore, the use of immunomodulators and biologics, and earlier consideration of elective surgery for medically refractory disease in elderly patients with IBD, should be emphasized and further evaluated to prevent complications of chronic corticosteroid(s) use and to prevent emergency surgery.

Pathophysiological responses from human gut microbiome

The human gastrointestinal tract harbors a vast collection of symbiotic microorganisms-collectively termed as “gut microbiome”. This microbiota has important effect in immune system and other host activities. Recent studies have suggested that alterations of the normal gut microbiota are associated with various human diseases and psychological disorders. The underlying cause, once proven, may provide novel insights into the importance of gut flora in human health. In this review, we give an attempt to describe how the alteration in the microbial community causes the development of certain widespread pathophysiological disorders; focusing on inflammatory bowel disease, colorectal cancer, obesity and autism. Proper knowledge about the host-microbiota interaction and linkage could be essential for the development of future personalized strategies of therapeutics.

Manipulation of the microbiota for treatment of IBS and IBD-challenges and controversies

There is compelling rationale for manipulating the microbiota to treat inflammatory bowel diseases (IBDs). Although studies of animal models of intestinal inflammation produced promising results, trials in humans have been disappointing. In contrast to IBD, the role of the microbiota in the development of irritable bowel syndrome (IBS) only recently has been considered, but early stage results have been encouraging. As pharmaceutical companies develop fewer truly novel agents for treatment of these disorders, consumers seek safer, long-term strategies to deal with chronic symptoms. We assess the rationale for modulating the microbiota for treatment of IBD and IBS, and discuss whether current concepts are simplistic and overstated or simply under-researched. Are claims exaggerated and expectations unrealistic? Difficulties with microbiota terminology and technologies, as well as differences among patients and the heterogeneity of these diseases, pose additional challenges in developing microbiota-based therapies for IBD and IBS.

The Natural Antimicrobial Enzyme Lysozyme is Up-Regulated in Gastrointestinal Inflammatory Conditions

The cells that line the mucosa of the human gastrointestinal tract (GI, that is, oral cavity, oesophagus, stomach, small intestine, large intestine, and rectum) are constantly challenged by adverse micro-environmental factors, such as different pH, enzymes, and bacterial flora. With exception of the oral cavity, these microenvironments also contain remnant cocktails of secreted enzymes and bacteria from upper organs along the tract. The density of the GI bacteria varies, from 103/mL near the gastric outlet, to 1010/mL at the ileocecal valve, to 1011 to 1012/mL in the colon. The total microbial population (ca. 1014) exceeds the total number of cells in the tract. It is, therefore, remarkable that despite the prima facie inauspicious mixture of harmful secretions and bacteria, the normal GI mucosa retains a healthy state of cell renewal. To counteract the hostile microenvironment, the GI epithelia react by speeding cell exfoliation (the GI mucosa has a turnover time of two to three days), by increasing peristalsis, by eliminating bacteria through secretion of plasma cell-immunoglobulins and by increasing production of natural antibacterial compounds, such as defensin-5 and lysozyme. Only recently, lysozyme was found up-regulated in Barrett's oesophagitis, chronic gastritis, gluten-induced atrophic duodenitis (coeliac disease), collagenous colitis, lymphocytic colitis, and Crohn's colitis. This up-regulation is a response directed to the special types of bacteria recently detected in these diseases. The aim of lysozyme up-regulation is to protect individual mucosal segments to chronic inflammation. The molecular mechanisms connected to the crosstalk between the intraluminal bacterial flora and the production of lysozyme released by the GI mucosae, are discussed. Bacterial resistance continues to exhaust our supply of commercial antibiotics. The potential use of lysozyme to treat infectious diseases is receiving much attention.

Molecular signatures for the dynamic process of establishing intestinal host-microbial homeostasis: potential for disease diagnostics?

PURPOSE OF REVIEW

The dynamic interplay of the intestinal microbiota and host has been the focus of many studies because of its impact on the health status in human life. Recent reports on the time-resolved immune and metabolic interactions between the host and microbiota, as well as the molecular signatures that mark this communication during the process of establishing a host-microbial relationship, are addressed here.

RECENT FINDINGS

During microbial colonization, the progressive impact of de-novo introduction of the gut microbiota on the host's physiology is tightly controlled by highly intertwined regulatory networks and achieves an efficient and balanced interplay between the host and its developing microbial community. Recent findings from germ-free mouse models have unravelled core transcriptional, metabolic and microbial signatures, which are proposed to orchestrate the molecular responses during the establishment of the multifaceted state of intestinal host-microbe homeostasis.

SUMMARY

Exploring the time-resolved dynamics of the host responses to the newly colonizing gut microbiota provides mechanistically critical understanding of the sequential host-microbe response cascades that lead to a homeostatic relationship. Thereby, these approaches can provide novel diagnostic tools and therapeutic targets, or either of the two, in humans for specific disorders associated with intestinal dysbiosis and loss of homeostasis.

Bridging immunity and lipid metabolism by gut microbiota

The human gut is a unique organ in which hundreds of different microbial species find their habitat and in which different host physiologic functions, such as digestion, nutrition, and immunity, coexist. Although all these players were studied separately for decades, recently, there has been an explosion of studies demonstrating the essential role for interactions between these components in gut function. Furthermore, new systems biology methods provide essential tools to study this complex system as a whole and to identify key elements that define the crosstalk between the gut microbiota, immunity, and metabolism. This review is devoted to several human diseases resulting from the disruption in this crosstalk, including immunodeficiency-associated and environmental enteropathies, celiac disease, inflammatory bowel disease, and obesity. We describe findings in experimental models of these diseases and in germ-free animals that help us understand the mechanisms and test new therapeutic strategies. We also discuss current challenges that the field is facing and propose that a new generation of antibiotics, prebiotics, and probiotics coupled with novel, systems biology-driven diagnostics will provide the basis for future personalized therapy.

Is folate involved in the pathogenesis of inflammatory bowel disease?

The inflammatory bowel diseases, Crohn's and ulcerative colitis, are common and a significant cause of morbidity. They were rare before the 1930's but the incidence has been increasing in both developed and developing countries. We have recently reported that the incidence in Nova Scotia, the area with one of the highest reported burden globally, is decreasing since 1997. We postulate that this decrease may be due to the addition of folate to cereals. This was mandated in 1998 but the process of fortification began in 1997. There is circumstantial evidence from epidemiology studies that a diet deficient in folate may have contributed to the global rise in these diseases. This hypothesis, if proven to be correct, has important implications for the prevention and treatment of these diseases.

Altered enteric microbiota ecology in interleukin 10-deficient mice during development and progression of intestinal inflammation

Inflammatory bowel diseases (IBD) result from dysregulated immune responses toward microbial and perhaps other luminal antigens in a genetically susceptible host, and are associated with altered composition and diversity of the intestinal microbiota. The interleukin 10-deficient (IL-10 (-/-) ) mouse has been widely used to model human IBD; however the specific alterations that occur in the intestinal microbiota of this mouse model during the onset of colonic inflammation have not yet been defined. The aim of our study was to define the changes in diversity and composition that occur in the intestinal microbiota of IL-10 (-/-) mice during the onset and progression of colonic inflammation. We used high throughput sequencing of the 16S rRNA gene to characterize the diversity and composition of formerly germ-free, wild-type and IL-10 (-/-) mice associated with the same intestinal microbiota over time. Following two weeks of colonization with a specific pathogen-free (SPF) microbiota we observed a significant increase in the diversity and richness of the intestinal microbiota of wild-type mice. In contrast, a progressive decrease in diversity and richness was observed at three and four weeks in IL-10 (-/-) mice. This decrease in diversity and richness was mirrored by an increase in Proteobacteria and Escherichia coli in IL-10 (-/-) mice. An increase in E. coli was also observed in conventionally raised IL-10 (-/-) mice at the point of colonic inflammation. Our data reports the sequential changes in diversity and composition of the intestinal microbiota in an immune-mediated mouse model that may help provide insights into the primary vs. secondary role of dysbiosis in human IBD patients.

Role of the gut microbiota in health and chronic gastrointestinal disease: understanding a hidden metabolic organ

The human gut microbiota has become the subject of extensive research in recent years and our knowledge of the resident species and their potential functional capacity is rapidly growing. Our gut harbours a complex community of over 100 trillion microbial cells which influence human physiology, metabolism, nutrition and immune function while disruption to the gut microbiota has been linked with gastrointestinal conditions such as inflammatory bowel disease and obesity. Here, we review the many significant recent studies that have centred on further enhancing our understanding of the complexity of intestinal communities as well as their genetic and metabolic potential. These have provided important information with respect to what constitutes a 'healthy gut microbiota' while furthering our understanding of the role of gut microbes in intestinal diseases. We also highlight recently developed genomic and other tools that are used to study the gut microbiome and, finally, we consider the manipulation of the gut microbiota as a potential therapeutic option to treat chronic gastrointestinal disease.

Cow's milk allergy, asthma, and pediatric IBD

We identified a total of 595 Finnish children born in 1994-2008 and diagnosed as having inflammatory bowel disease (IBD) by October 2010 from the National Reimbursement Register (based on certificates including the diagnostic criteria) to determine whether the presence of cow's milk allergy (CMA) or asthma is associated with the risk of contracting IBD (altogether 2380 matched controls). A diagnosis of CMA in infancy was associated with Crohn disease (odds ratio [OR] 1.92, confidence interval [CI] 1.09-3.36, P < 0.05) and ulcerative colitis (OR 1.71, CI 1.04-2.83, P < 0.05), but childhood asthma only with Crohn disease (OR 2.33, CI 1.41-3.86, P = 0.001). Thus, CMA in infants is a risk factor for contracting pediatric IBD and accordingly, asthma for Crohn disease.

The colonic microbiota in health and disease

PURPOSE OF REVIEW

Diverse research interests have converged on the gut microbiota because of its contribution to immune development, mucosal homeostasis and to the pathogenesis of a diversity of intestinal and extraintestinal disorders. Recent landmark findings are addressed here.

RECENT FINDINGS

The impact of lifestyle, including dietary changes and antibiotics, on the microbiota has been mechanistically linked with disease risk. Microbial, immune and metabolic signalling are mutually interactive, with each of these being regulated by diet. Although changes in the microbiota have been found in several disorders and may have important therapeutic implications, some components of the commensal microbiota may behave like pathogens (pathobionts) depending on the context and host susceptibility.

SUMMARY

Advances in understanding host-microbe interactions in the gut continue apace, they are relevant to a diversity of infectious, inflammatory, neoplastic and metabolic disorders and are poised for clinical translation.

Probiotics in transition

Despite the hyperbole often linked with a popular research field, the scientific rationale for probiotics is sound. The probiotic concept is not new but is undergoing transition as knowledge of the gut microbiota in health and disease becomes translated to the clinic. Operationally, a probiotic represents a mimic of and/or supplement to the normal gut microbiota. Much confusion has arisen among consumers because of media misportrayals of probiotics as all being the same. However, with clarification of the molecular basis of host-microbe interactions, the selection criteria for probiotics and the delineation of their distinct mechanisms of action are improving. Most probiotics are from the genus Lactobacillus or Bifidobacterium; this is likely to change and diversify. Similarly, the development of new therapeutic strategies, such as the development of phagebiotics, psychobiotics, and genetically modified pharmabiotics, is poised to become a therapeutic reality.

Summary of the 24(th) Marabou Symposium: Nutrition and the human microbiome

This summary covers the articles and attributed discussion in the present supplement, which resulted from the 24(th) Marabou Symposium titled "Nutrition and the Human Microbiome", which was held in Stockholm in 2011 with the participation of about 40 global experts in microbiology, physiology, biology, and medicine. The individual articles address a number of topics related to the human microbiome; the attributed discussion, however, offers much more on the nature of the current scientific debate and provides insight into new opportunities for research as well as possible effects of the gut microbes, ranging from possible prenatal epigenetic effects to brain function and behavior.