A review of the effect of iron supplementation on the gut microbiota of children in developing countries and the impact of prebiotics.

Iron is essential for many physiological functions of the body, and it is required for normal growth and development. Iron deficiency (ID) is the most common form of micronutrient malnutrition and is particularly prevalent in infants and young children in developing countries. Iron supplementation is considered the most effective strategy to combat the risk of ID and ID anaemia (IDA) in infants, although iron supplements cause a range of deleterious gut-related problems in malnourished children. The purpose of this review is to assess the available evidence on the effect of iron supplementation on the gut microbiota during childhood ID and to further assess whether prebiotics offer any benefits for iron supplementation. Prebiotics are well known to improve gut-microbial health in children, and recent reports indicate that prebiotics can mitigate the adverse gut-related effects of iron supplementation in children with ID and IDA. Thus, provision of prebiotics alongside iron supplements has the potential for an enhanced strategy for combatting ID and IDA among children in the developing world. However, further understanding is required before the benefit of such combined treatments of ID in nutritionally deprived children across populations can be fully confirmed. Such enhanced understanding is of high relevance in resource-poor countries where ID, poor sanitation and hygiene, alongside inadequate access to good drinking water and poor health systems, are serious public health concerns.

Do high-protein diets have the potential to reduce gut barrier function in a sex-dependent manner?

PURPOSE: Impaired gut barrier function is associated with systemic inflammation and many chronic diseases. Undigested dietary proteins are fermented in the colon by the gut microbiota which produces nitrogenous metabolites shown to reduce barrier function in vitro. With growing evidence of sex-based differences in gut microbiotas, we determined whether there were sex by dietary protein interactions which could differentially impact barrier function via microbiota modification. METHODS: Fermentation systems were inoculated with faeces from healthy males (n = 5) and females (n = 5) and supplemented with 0.9 g of non-hydrolysed proteins sourced from whey, fish, milk, soya, egg, pea, or mycoprotein. Microbial populations were quantified using fluorescence in situ hybridisation with flow cytometry. Metabolite concentrations were analysed using gas chromatography, solid phase microextraction coupled with gas chromatography-mass spectrometry and ELISA. RESULTS: Increased protein availability resulted in increased proteolytic Bacteroides spp (p < 0.01) and Clostridium coccoides (p < 0.01), along with increased phenol (p < 0.01), p-cresol (p < 0.01), indole (p = 0.018) and ammonia (p < 0.01), varying by protein type. Counts of Clostridium cluster IX (p = 0.03) and concentration of p-cresol (p = 0.025) increased in males, while females produced more ammonia (p = 0.02), irrespective of protein type. Further, we observed significant sex-protein interactions affecting bacterial populations and metabolites (p < 0.005). CONCLUSIONS: Our findings suggest that protein fermentation by the gut microbiota in vitro is influenced by both protein source and the donor's sex. Should these results be confirmed through human studies, they could have major implications for developing dietary recommendations tailored by sex to prevent chronic illnesses.

Comparison of prebiotic candidates in ulcerative colitis using an in vitro fermentation model.

AIMS: This study explored the effect of three different prebiotics, the human milk oligosaccharide 2'-fucosyllactose (2'-FL), an oligofructose-enriched inulin (fructo-oligosaccharide, or FOS), and a galacto-oligosaccaride (GOS) mixture, on the faecal microbiota from patients with ulcerative colitis (UC) using in vitro batch culture fermentation models. Changes in bacterial groups and short-chain fatty acid (SCFA) production were compared. METHODS AND RESULTS: In vitro pH controlled batch culture fermentation was carried out over 48 h on samples from three healthy controls and three patients with active UC. Four vessels were run, one negative control and one for each of the prebiotic substrates. Bacterial enumeration was carried out using fluorescence in situ hybridization with flow cytometry. SCFA quantification was performed using gas chromatography mass spectrometry. All substrates had a positive effect on the gut microbiota and led to significant increases in total SCFA and propionate concentrations at 48 h. 2'-FL was the only substrate to significantly increase acetate and led to the greatest increase in total SCFA concentration at 48 h. 2'-FL best suppressed Desulfovibrio spp., a pathogen associated with UC. CONCLUSIONS: 2'FL, FOS, and GOS all significantly improved the gut microbiota in this in vitro study and also led to increased SCFA.

A review on the use of prebiotics in ulcerative colitis.

The gut microbiome in the inflammatory bowel disease, ulcerative colitis (UC), is different to that of healthy controls. Patients with UC have relative reductions in abundance of Firmicutes and Bifidobacterium in the colon, and an increase in sulfate-reducing bacteria. Prebiotics are dietary substrates which are selectively metabolised by the human colonic microbiota to confer health benefits to the host. This review explores our current understanding of the potential benefits of prebiotics on various clinical, biochemical, and microbiological endpoints in UC, including new perspectives gained from recent studies in the field. This review looks to the future and highlights the need for appropriately designed trials to explore this potentially exciting new avenue for the treatment of UC.

The Effect of Probiotic Bacteria on Composition and Metabolite Production of Faecal Microbiota Using In Vitro Batch Cultures.

Probiotic supplements are increasingly being used to target the gut microbiome with a view to improving cognitive and psychological function via the gut-brain axis. One possible mechanism behind the effect of probiotics is through alterations to microbially-derived metabolites including short-chain fatty acids (SCFA) and neurotransmitters. However, research to date has largely been conducted in animal models or under conditions irrelevant to the human gastrointestinal tract (GIT). The aim of the current work was therefore to use anaerobic, pH controlled in vitro batch cultures to (a) assess the production of neuroactive metabolites in human faecal microbiota under conditions relevant to the human GIT, and (b) to explore how several pre-selected probiotic strains may affect bacterial composition and metabolite production. Enumeration of bacteria was assessed using fluorescence in situ hybridisation with flow cytometry, and concentrations of SCFAs and neurotransmitters were measured using gas chromatography and liquid chromatography mass spectroscopy, respectively. GABA, serotonin, tryptophan, and dopamine were successfully detected, suggesting some level of microbial derivation. The addition of Lactococcus lactis W58 and Lactobacillus rhamnosus W198 resulted in a significant increase in lactate after 8 h of fermentation, while no significant effect of probiotics on bacterial composition or neurotransmitter production was found.

Chronic consumption of a blend of inulin and arabinoxylan reduces energy intake in an ad libitum meal but does not influence perceptions of appetite and satiety: a randomised control-controlled crossover trial.

PURPOSE: Prebiotic foods can be used to increase production of short-chain fatty acids (SCFA) in the gut. Of the SCFA, propionate is credited with the strongest anorectic activity. In previous work, a 50/50 blend of inulin and arabinoxylan was produced (I + AX) that significantly increased propionate production in an in vitro gut model. This study sought to establish whether chronic consumption of a prebiotic blend of I + AX decreases appetite and energy intake and increases intestinal propionate production in human participants. METHODS: MIXSAT (clinicaltrials.gov id: NCT02846454, August 2016) was a double-blind randomised acute-within-chronic crossover feeding trial in healthy adult men (n = 20). Treatments were 8 g per day I + AX for 21 days or weight-matched maltodextrin control. The primary outcome measure was perceived satiety and appetite during an acute study visit. Secondary outcomes were energy intake in an ad libitum meal, faecal SCFA concentration, and faecal microbiota composition. RESULTS: Perceived satiety and appetite were not affected by the intervention. I + AX was associated with a reduction in energy intake in an ad libitum meal, increased faecal SCFA concentration, and an increase in cell counts of Bifidobacteria, Lactobacilli, and other microbial genera associated with health. IMPLICATIONS: Chronic consumption of this blend of prebiotics decreased energy intake in a single sitting. Further studies are needed to confirm mechanism of action and to determine whether this might be useful in weight control.

Impact of inorganic iron and haem on the human gut microbiota; An in vitro batch-culture approach.

Although iron is an essential nutrient for humans, as well as for almost all other organisms, it is poorly absorbed (~15%) from the diet such that most passes through the upper gut into the large intestine. The colonic microbiota is thus exposed to, and potentially influenced by, such residual iron which could have an impact on human health. The aim of the research described here is to determine how the major forms of dietary iron (inorganic iron and haem) influence metabolic activity and composition of the human gut microbiota by utilizing an in vitro parallel, pH-controlled anaerobic batch culture approach. Controlled iron provision was enabled by the design of a 'modified' low-iron gut-model medium whereby background iron content was reduced from 28 to 5 µM. Thus, the impact of both low and high levels of inorganic and haem iron (18-180 µM and 7.7-77 µM, respectively) could be explored. Gut-microbiota composition was determined using next generation sequencing (NGS) based community profiling (16S rRNA gene sequencing) and flow-fluorescent in situ hybridization (FISH). Metabolic-end products (organic acids) were quantified using gas chromatography (GC) and iron incorporation was estimated by inductively coupled plasma optical emission spectroscopy (ICP-OES). Results showed that differences in iron regime induced significant changes in microbiota composition when low (0.1% w/v) fecal inoculation levels were employed. An increase in haem levels from 7.7 to 77 µM (standard levels employed in gut culture studies) resulted in reduced microbial diversity, a significant increase in Enterobacteriaceae and lower short chain fatty acid (SCFA) production. These effects were countered when 18 µM inorganic iron was also included into the growth medium. The results therefore suggest that high-dietary haem may have a detrimental effect on health since the resulting changes in microbiota composition and SCFA production are indicators of an unhealthy gut. The results also demonstrate that employing a low inoculum together with a low-iron gut-model medium facilitated in vitro investigation of the relationship between iron and the gut microbiota.

NMR Metabolomics and DNA Sequencing of Escherichia coli and Staphylococcus aureus Cultures Treated with Hydrolyzable Tannins.

Escherichia coli and Staphylococcus aureus are globally among the most prominent bacterial strains associated with antibacterial resistance-caused deaths. Naturally occurring polyphenols, such as hydrolyzable tannins, have been shown to potently inhibit E. coli and S. aureus. The current study investigated the metabolome changes of E. coli and S. aureus cultures after treatments with different hydrolyzable tannins using an NMR metabolomics approach. Additionally, the effect of these tannin treatments influencing a more complex bacterial system was studied in a biomimetic setting with fecal samples inoculated into the growth medium. Metabolite concentration changes were observed in all three scenarios: E. coli, S. aureus, and fecal batch culture. The metabolome of E. coli was more altered by the tannin treatments than S. aureus when compared to control cultures. A dimeric hydrolyzable tannin, rugosin D, was found to be the most effective of the studied compounds in influencing bacterial metabolome changes and in inhibiting E. coli and S. aureus growth. It was also observed that the tannin structure should have both hydrophobic and hydrophilic regions to efficiently influence E. coli and S. aureus growth.

Staphylococcus aureus FadB is a dehydrogenase that mediates cholate resistance and survival under human colonic conditions.

Staphylococcus aureus is a common colonizer of the human gut and in doing so it must be able to resist the actions of the host's innate defences. Bile salts are a class of molecules that possess potent antibacterial activity that control growth. Bacteria that colonize and survive in that niche must be able to resist the action of bile salts, but the mechanisms by which S. aureus does so are poorly understood. Here we show that FadB is a bile-induced oxidoreductase which mediates bile salt resistance and when heterologously expressed in Escherichia coli renders them resistant. Deletion of fadB attenuated survival of S. aureus in a model of the human distal colon.

Gut microbial modulation by culinary herbs and spices.

Culinary herbs and spices have previously been recognised for their potential impact on health through antioxidant and antimicrobial properties. They may also be promotors of positive microbial modulation by stimulating beneficial gut bacteria during fermentation, increasing the production of short chain fatty acids and thereby exhibiting a prebiotic effect. In the present paper, current literature around herb and spice consumption, gut microbiota modulation and prospective health benefits were reviewed. Herb and spice consumption can positively modulate gut microbes and possibly play an important role in inflammation related afflictions such as obesity. Current literature indicates that few human studies have been conducted to confirm the impact of herb and spice consumption on gut microbiota in connection with prospective health outcomes and inconsistencies in conclusions therefore remain.

Cranberry Arabino-Xyloglucan and Pectic Oligosaccharides Induce Lactobacillus Growth and Short-Chain Fatty Acid Production.

Numerous health benefits have been reported from the consumption of cranberry-derived products, and recent studies have identified bioactive polysaccharides and oligosaccharides from cranberry pomace. This study aimed to further characterize xyloglucan and pectic oligosaccharide structures from pectinase-treated cranberry pomace and measure the growth and short-chain fatty acid production of 86 Lactobacillus strains using a cranberry oligosaccharide fraction as the carbon source. In addition to arabino-xyloglucan structures, cranberry oligosaccharides included pectic rhamnogalacturonan I which was methyl-esterified, acetylated and contained arabino-galacto-oligosaccharide side chains and a 4,5-unsaturated function at the non-reducing end. When grown on cranberry oligosaccharides, ten Lactobacillus strains reached a final culture density (ΔOD) ≥ 0.50 after 24 h incubation at 32 °C, which was comparable to L. plantarum ATCC BAA 793. All strains produced lactic, acetic, and propionic acids, and all but three strains produced butyric acid. This study demonstrated that the ability to metabolize cranberry oligosaccharides is Lactobacillus strain specific, with some strains having the potential to be probiotics, and for the first time showed these ten strains were capable of growth on this carbon source. The novel cranberry pectic and arabino-xyloglucan oligosaccharide structures reported here combined with the Lactobacillus strains that can metabolize cranberry oligosaccharides and produce short-chain fatty acids, have excellent potential as health-promoting synbiotics.

Perspective: Leveraging the Gut Microbiota to Predict Personalized Responses to Dietary, Prebiotic, and Probiotic Interventions.

Humans often show variable responses to dietary, prebiotic, and probiotic interventions. Emerging evidence indicates that the gut microbiota is a key determinant for this population heterogeneity. Here, we provide an overview of some of the major computational and experimental tools being applied to critical questions of microbiota-mediated personalized nutrition and health. First, we discuss the latest advances in in silico modeling of the microbiota-nutrition-health axis, including the application of statistical, mechanistic, and hybrid artificial intelligence models. Second, we address high-throughput in vitro techniques for assessing interindividual heterogeneity, from ex vivo batch culturing of stool and continuous culturing in anaerobic bioreactors, to more sophisticated organ-on-a-chip models that integrate both host and microbial compartments. Third, we explore in vivo approaches for better understanding of personalized, microbiota-mediated responses to diet, prebiotics, and probiotics, from nonhuman animal models and human observational studies, to human feeding trials and crossover interventions. We highlight examples of existing, consumer-facing precision nutrition platforms that are currently leveraging the gut microbiota. Furthermore, we discuss how the integration of a broader set of the tools and techniques described in this piece can generate the data necessary to support a greater diversity of precision nutrition strategies. Finally, we present a vision of a precision nutrition and healthcare future, which leverages the gut microbiota to design effective, individual-specific interventions.

Systematic Review of the Effects of Exercise and Physical Activity on the Gut Microbiome of Older Adults.

Recent evidence suggests that exercise/physical activity (PA) can beneficially alter the gut microbiome composition of young people, but little is known about its effects in older adults. The aim of this systematic review was to summarize results of human studies that have assessed the effects/associations of PA/exercise on the gut microbiome of older adults and to better understand whether this can help promote healthy ageing. Seven studies were included in the review and overall, exercise and increased amounts of PA were associated with decreases in the abundance of several well-known harmful taxa and increases in the abundance of health-promoting taxa. Altogether, the findings from the included studies suggest that exercise/PA have a beneficial impact on the gut health of older adults by improving the gut microbiome composition. However, due to methodological and sampling disparities, it was not possible to reach a consensus on which taxa were most affected by exercise or PA.

Hay versus haylage: Forage type influences the equine urinary metabonome and faecal microbiota.

BACKGROUND: Gut microbial communities are increasingly being linked to diseases in animals and humans. Obesity and its associated diseases are a concern for horse owners and veterinarians, and there is a growing interest in the link among diet, the intestinal microbiota and metabolic disease. OBJECTIVES: Assess the influence of long-term hay or haylage feeding on the microbiota and metabolomes of 20 Welsh mountain ponies. STUDY DESIGN: Longitudinal study. METHODS: Urine, faeces and blood were collected from 20 ponies on a monthly basis over a 13-month period. Urine and faeces were analysed using proton magnetic resonance (1 H NMR) spectroscopy and faecal bacterial DNA underwent 16S rRNA gene sequencing. RESULTS: Faecal bacterial community profiles were observed to be different for the two groups, with discriminant analysis identifying 102 bacterial groups (or operational taxonomic units, OTUs) that differed in relative abundance in accordance with forage type. Urinary metabolic profiles of the hay- and haylage-fed ponies were significantly different during 12 of the 13 mo of the study. Notably, the urinary excretion of hippurate was greater in the hay-fed ponies for the duration of the study, while ethyl-glucoside excretion was higher in the haylage-fed ponies. MAIN LIMITATIONS: The study was undertaken over a 13-month period and both groups of ponies had access to pasture during the summer months. CONCLUSIONS: The data generated from this study suggest that the choice of forage may have implications for the intestinal microbiota and metabolism of ponies and, therefore, potentially their health status. Understanding the potential implication of feeding a particular type of forage will enable horse owners to make more informed choices with regard to feed, especially if their horse or pony is prone to weight gain.

An In Vitro Approach to Studying the Microbial Community and Impact of Pre and Probiotics under Anorexia Nervosa Related Dietary Restrictions.

Individuals with anorexia nervosa (AN) often suffer psychological and gastrointestinal problems consistent with a dysregulated gut microbial community. Psychobiotics have been postulated to modify microbiota and improve mental well-being and gut symptoms, but there is currently a lack of evidence for such approaches in AN. The aim of this study was to use an in vitro colonic model to evaluate the impact of dietary restrictions associated with AN on the intestinal ecosystem and to assess the impact of pre and probiotic intervention. Bacteriology was quantified using flow cytometry combined with fluorescence in situ hybridisation and metabolic end products (including neurotransmitters) by gas chromatography and liquid chromatography mass spectrometry Consistent with previous research, the nutritional changes significantly reduced total microbiota and metabolites compared with healthy conditions. Pre and probiotic supplementation on restricted conditions enhanced the microbial community and modulated metabolic activity to resemble that of a healthy diet. The model system indicates that nutritional changes associated with AN can impact the microbial community, and that these changes can, at least in part, be restored through the use of pre and probiotic interventions.

Post-weaning A1/A2 ß-casein milk intake modulates depressive-like behavior, brain µ-opioid receptors, and the metabolome of rats.

The postnatal period is critical for brain and behavioral development and is sensitive to environmental stimuli, such as nutrition. Prevention of weaning from maternal milk was previously shown to cause depressive-like behavior in rats. Additionally, loss of dietary casein was found to act as a developmental trigger for a population of brain opioid receptors. Here, we explore the effect of exposure to milk containing A1 and A2 ß-casein beyond weaning. A1 but not A2 ß-casein milk significantly increased stress-induced immobility in rats, concomitant with an increased abundance of Clostridium histolyticum bacterial group in the caecum and colon of A1 ß-casein fed animals, brain region-specific alterations of µ-opioid and oxytocin receptors, and modifications in urinary biochemical profiles. Moreover, urinary gut microbial metabolites strongly correlated with altered brain metabolites. These findings suggest that consumption of milk containing A1 ß-casein beyond weaning age may affect mood via a possible gut-brain axis mechanism.

Sulfation of Arabinogalactan Proteins Confers Privileged Nutrient Status to Bacteroides plebeius.

The human gut microbiota (HGM) contributes to the physiology and health of its host. The health benefits provided by dietary manipulation of the HGM require knowledge of how glycans, the major nutrients available to this ecosystem, are metabolized. Arabinogalactan proteins (AGPs) are a ubiquitous feature of plant polysaccharides available to the HGM. Although the galactan backbone and galactooligosaccharide side chains of AGPs are conserved, the decorations of these structures are highly variable. Here, we tested the hypothesis that these variations in arabinogalactan decoration provide a selection mechanism for specific Bacteroides species within the HGM. The data showed that only a single bacterium, B. plebeius, grew on red wine AGP (Wi-AGP) and seaweed AGP (SW-AGP) in mono- or mixed culture. Wi-AGP thus acts as a privileged nutrient for a Bacteroides species within the HGM that utilizes marine and terrestrial plant glycans. The B. plebeius polysaccharide utilization loci (PULs) upregulated by AGPs encoded a polysaccharide lyase, located in the enzyme family GH145, which hydrolyzed Rha-Glc linkages in Wi-AGP. Further analysis of GH145 identified an enzyme with two active sites that displayed glycoside hydrolase and lyase activities, respectively, which conferred substrate flexibility for different AGPs. The AGP-degrading apparatus of B. plebeius also contained a sulfatase, BpS1_8, active on SW-AGP and Wi-AGP, which played a pivotal role in the utilization of these glycans by the bacterium. BpS1_8 enabled other Bacteroides species to access the sulfated AGPs, providing a route to introducing privileged nutrient utilization into probiotic and commensal organisms that could improve human health. IMPORTANCE Dietary manipulation of the HGM requires knowledge of how glycans available to this ecosystem are metabolized. The variable structures that decorate the core component of plant AGPs may influence their utilization by specific organisms within the HGM. Here, we evaluated the ability of Bacteroides species to utilize a marine and terrestrial AGP. The data showed that a single bacterium, B. plebeius, grew on Wi-AGP and SW-AGP in mono- or mixed culture. Wi-AGP is thus a privileged nutrient for a Bacteroides species that utilizes marine and terrestrial plant glycans. A key component of the AGP-degrading apparatus of B. plebeius is a sulfatase that conferred the ability of the bacterium to utilize these glycans. The enzyme enabled other Bacteroides species to access the sulfated AGPs, providing a route to introducing privileged nutrient utilization into probiotic and commensal organisms that could improve human health.

Malnutrition and Gut Microbiota in Children.

Malnutrition continues to threaten the lives of millions across the world, with children being hardest hit. Although inadequate access to food and infectious disease are the primary causes of childhood malnutrition, the gut microbiota may also contribute. This review considers the evidence on the role of diet in modifying the gut microbiota, and how the microbiota impacts childhood malnutrition. It is widely understood that the gut microbiota of children is influenced by diet, which, in turn, can impact child nutritional status. Additionally, diarrhoea, a major contributor to malnutrition, is induced by pathogenic elements of the gut microbiota. Diarrhoea leads to malabsorption of essential nutrients and reduced energy availability resulting in weight loss, which can lead to malnutrition. Alterations in gut microbiota of severe acute malnourished (SAM) children include increased Proteobacteria and decreased Bacteroides levels. Additionally, the gut microbiota of SAM children exhibits lower relative diversity compared with healthy children. Thus, the data indicate a link between gut microbiota and malnutrition in children, suggesting that treatment of childhood malnutrition should include measures that support a healthy gut microbiota. This could be of particular relevance in sub-Saharan Africa and Asia where prevalence of malnutrition remains a major threat to the lives of millions.