Inhibitory effects of soybean oligosaccharides and water-soluble soybean fibre on formation of putrefactive compounds from soy protein by gut microbiota

The role of fiber in modulating plant protein-induced metabolic responses

The rising consumption of plant protein foods and the emergence of meat alternatives have prompted interest in the health benefits of such products, which contain fiber in addition to protein. This review investigates the effect of fiber on plant-based protein metabolism and evaluates its contribution to gut-derived health impacts. Plant proteins, which often come with added fiber, can have varying health outcomes. Factors such as processing and the presence of fiber and starch influence the digestibility of plant proteins, potentially leading to increased proteolytic fermentation in the gut and the production of harmful metabolites. However, fermentable fiber can counteract this effect by serving as a primary substrate for gut microbes, decreasing proteolytic activity. The increased amount of fiber, rather than the protein source itself, plays a significant role in the observed health benefits of plant-based diets in human studies. Differences between extrinsic and intrinsic fiber in the food matrix further impact protein fermentation and digestibility. Thus, in novel protein products without naturally occurring fiber, the health impact may differ from conventional plant protein sources. The influence of various fibers on plant-based protein metabolism throughout the gastrointestinal tract is not fully understood, necessitating further research.

Dietary fibre directs microbial tryptophan metabolism via metabolic interactions in the gut microbiota

Tryptophan is catabolized by gut microorganisms resulting in a wide range of metabolites implicated in both beneficial and adverse host effects. How gut microbial tryptophan metabolism is directed towards indole, associated with chronic kidney disease, or towards protective indolelactic acid (ILA) and indolepropionic acid (IPA) is unclear. Here we used in vitro culturing and animal experiments to assess gut microbial competition for tryptophan and the resulting metabolites in a controlled three-species defined community and in complex undefined human faecal communities. The generation of specific tryptophan-derived metabolites was not predominantly determined by the abundance of tryptophan-metabolizing bacteria, but rather by substrate-dependent regulation of specific metabolic pathways. Indole-producing Escherichia coli and ILA- and IPA-producing Clostridium sporogenes competed for tryptophan within the three-species community in vitro and in vivo. Importantly, fibre-degrading Bacteroides thetaiotaomicron affected this competition by cross-feeding monosaccharides to E. coli. This inhibited indole production through catabolite repression, thus making more tryptophan available to C. sporogenes, resulting in increased ILA and IPA production. The fibre-dependent reduction in indole was confirmed using human faecal cultures and faecal-microbiota-transplanted gnotobiotic mice. Our findings explain why consumption of fermentable fibres suppresses indole production but promotes the generation of other tryptophan metabolites associated with health benefits.

Microbial tryptophan catabolism as an actionable target via diet-microbiome interactions

In recent years, the role of microbial tryptophan (Trp) catabolism in host-microbiota crosstalk has become a major area of scientific interest. Microbiota-derived Trp catabolites positively contribute to intestinal and systemic homeostasis by acting as ligands of aryl hydrocarbon receptor and pregnane X receptor, and as signaling molecules in microbial communities. Accumulating evidence suggests that microbial Trp catabolism could be therapeutic targets in treating human diseases. A number of bacteria and metabolic pathways have been identified to be responsible for the conversion of Trp in the intestine. Interestingly, many Trp-degrading bacteria can benefit from the supplementation of specific dietary fibers and polyphenols, which in turn increase the microbial production of beneficial Trp catabolites. Thus, this review aims to highlight the emerging role of diets and food components, i.e., food matrix, fiber, and polyphenol, in modulating the microbial catabolism of Trp and discuss the opportunities for potential therapeutic interventions via specifically designed diets targeting the Trp-microbiome axis.

Detection of typical indigenous gut bacteria related to kanpyo Lagenaria siceraria var. hispida powder in murine caecum and human faecal cultures

Kanpyo (KP) is an edible dried product produced by peeling the fruit of the gourd Lagenaria siceraria var. hispida; it is used in the traditional Japanese cuisine. The health functionality of KP due to its rich dietary fibre is expected to include a possible combined effect of KP-responsive indigenous gut bacteria (KP-RIB). However, its effect on the gut microbiota is unclear. To determine the effects of the KP on the gut microbiota and their host, Institute of Cancer Research mice were fed a high-sucrose diet containing no fibre (NF) or 5% (w/w) KP for 14 days, and their caecal microbiota was analysed by 16S rRNA (V4) amplicon sequencing. Higher faecal frequency and weight and lower spleen weight and spleen tumour necrosis factor-α levels were observed in KP-fed mice than in NF-fed mice (p < 0.05). KP increased and decreased the abundance of short-chain fatty acid producer Lachnospiraceae and obesity-inflammation related Allobaculum species, respectively. In the case of human faecal cultures, stool samples from five healthy volunteers were inoculated and incubated at 37 °C for 24 h anaerobically; 3.2% (w/v) KP suppressed putrefactive compounds (indole, phenol, and ammonia). KP increased butyrate-producer Faecalibacterium, acetate/lactate-producer Bifidobacterium, and Lachnospira. Furthermore, KP cultures showed high antioxidant and RAW264.7 macrophage cell activation capacities. These results suggest that KP-RIB and KP intake may synergistically affect host health. However, further studies are required to clarify the synergistic effects of KP and KP-RIB.

The Role of Carbohydrate Intake on the Gut Microbiome: A Weight of Evidence Systematic Review

(1) Background: Carbohydrates are the most important source of nutritional energy for the human body. Carbohydrate digestion, metabolism, and their role in the gut microbiota modulation are the focus of multiple studies. The objective of this weight of evidence systematic review is to investigate the potential relationship between ingested carbohydrates and the gut microbiota composition at different taxonomic levels. (2) Methods: Weight of evidence and information value techniques were used to evaluate the relationship between dietary carbohydrates and the relative abundance of different bacterial taxa in the gut microbiota. (3) Results: The obtained results show that the types of carbohydrates that have a high information value are: soluble fiber with Bacteroides increase, insoluble fiber with Bacteroides and Actinobacteria increase, and Firmicutes decrease. Oligosaccharides with Lactobacillus increase and Enterococcus decrease. Gelatinized starches with Prevotella increase. Starches and resistant starches with Blautia decrease and Firmicutes increase. (4) Conclusions: This work provides, for the first time, an integrative review of the subject by using statistical techniques that have not been previously employed in microbiota reviews.

Effects of Food Factors and Processing on Protein Digestibility and Gut Microbiota

Protein is an essential macronutrient. The nutritional needs of dietary proteins are met by digestion and absorption in the small intestine. Indigestible proteins are further metabolized in the gut and produce metabolites via protein fermentation. Thus, protein indigestibility exerts a wide range of effects on gut microbiota composition and function. This review aims to discuss protein digestibility, the effects of food factors, such as protein sources, intake level, and amino acid composition, and making meat analogues. Besides, it provides an inventory of antinutritional factors and processing techniques that influence protein digestibility and, consequently, the diversity and composition of intestinal microbiota. Future studies are warranted to understand the implication of plant-based analogues on protein digestibility and gut microbiota and to elucidate the mechanisms concerning protein digestibility to host gut microbiota using various omics techniques.

Detection of typical indigenous gut bacteria related to turmeric (Curcuma longa) powder in mouse caecum and human faecal cultures

BACKGROUND

Turmeric (Curcuma longa; TM) is widely used as a spice and possesses anti-inflammatory, antioxidant, and antibacterial properties. The relationship between TM functions and gut microbiota is still unclear.

METHODS AND RESULTS

To investigate the effect of TM on gut microbiota and to identify indigenous gut bacteria that are responsive to TM, we fed Institute of Cancer Research mice a diet containing either no fibre (NF, n = 6) or 5% (w/w) TM (n = 6) for 14 days. Moreover, we obtained human stool samples from four healthy volunteers and incubated the samples without (control) or with 2% (w/v) TM at 37 °C for 24 h. Subsequently, microbiota analysis in murine caecal samples and human faecal cultures was performed using 16S rRNA (V4) amplicon sequencing. Higher faecal weights (p < 0.01) and lower plasma triacylglycerol levels (p < 0.05) were measured in the TM-fed mice than in the NF-fed mice. Furthermore, TM feeding increased the abundance of butyrate-producing and other short-chain fatty acid (SCFA)-producing bacteria in mice as well as in human faecal cultures, and Roseburia bacteria were detected as TM-responsive indigenous gut bacteria (TM-RIB) both in mice and in human faecal cultures. Lastly, in the case of human faecal cultures, SCFA contents and antioxidant properties were higher in TM cultures than in control cultures (p < 0.05).

CONCLUSION

TM appears to hold the potential to positively affect the host by altering the gut microbiota. Further studies are required to clarify the synergistic effects of TM and TM-RIB.

In Vitro Fermentability of Soybean Oligosaccharides from Wastewater of Tofu Production

Soybean oligosaccharides (SBOS) isolated from wastewater of tofu production were studied in terms of their structural characteristics and in vitro fermentation by human fecal inocula. Three sub-fractions named Z1 (14%), Z2 (13%), and Z3 (17%) were obtained by Sephadex G-15 column separation. Z1 contained mainly stachyose; Z2 and Z3 contained stachyose, raffinose, and sucrose with different relative percentages. The in vitro batch fermentation model of human intestinal bacteria including 0, 12, 24, and 48 h was used to investigate the fermentation characteristics of SBOS. According to the results, during the fermentation process, the molecular weight of oligosaccharides decreased significantly with increasing fermentation time, indicating that oligosaccharides could be utilized and degraded by the colonic microbiota. Furthermore, SBOS could significantly promote the production of short-chain fatty acids (SCFAs), especially acetic, propionic, and butyric acids. SBOS increased the abundance of Firmicutes, while that of Proteobacteria was decreased. Additionally, SBOS could promote the proliferation of Dialister, Bacteroides, and Akkermansia at the genus level. Therefore, SBOS can be potentially used as prebiotic promoting gut health.

Effect of Dietary Protein and Processing on Gut Microbiota-A Systematic Review

The effect of diet on the composition of gut microbiota and the consequent impact on disease risk have been of expanding interest. The present review focuses on current insights of changes associated with dietary protein-induced gut microbial populations and examines their potential roles in the metabolism, health, and disease of animals. Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) protocol was used, and 29 highly relevant articles were obtained, which included 6 mouse studies, 7 pig studies, 15 rat studies, and 1 in vitro study. Analysis of these studies indicated that several factors, such as protein source, protein content, dietary composition (such as carbohydrate content), glycation of protein, processing factors, and protein oxidation, affect the digestibility and bioavailability of dietary proteins. These factors can influence protein fermentation, absorption, and functional properties in the gut and, consequently, impact the composition of gut microbiota and affect human health. While gut microbiota can release metabolites that can affect host physiology either positively or negatively, the selection of quality of protein and suitable food processing conditions are important to have a positive effect of dietary protein on gut microbiota and human health.

The bioavailability of soybean polysaccharides and their metabolites on gut microbiota in the simulator of the human intestinal microbial ecosystem (SHIME)

The present study aimed to investigate the bioavailability of soybean polysaccharides and their metabolites on gut microbiota in the simulator of the human intestinal microbial ecosystem (SHIME). The effects of soybean polysaccharides on probiotics and pathogenic bacteria were investigated in vitro. Our results showed that soybean polysaccharides were only partially degraded in the oral, gastric, and small intestinal compartments of the SHIME. Moreover, the polysaccharides could be mainly broken down and utilized by the gut microbiota in the colon of the SHIME. Soybean polysaccharides could significantly reduce the ratio of Firmicutes to Bacteroidetes at the phylum level. Therefore, the number of beneficial bacteria were noticeably enhanced, and the pathogenic bacteria were inhibited. Furthermore, soybean polysaccharides promoted the growth of probiotics and improved the ability of these probiotics to inhibit pathogenic bacteria. Therefore, soybean polysaccharides could potentially be functional food to prevent disease by promoting gut health.

Impact of a fermented soy beverage supplemented with acerola by-product on the gut microbiota from lean and obese subjects using an in vitro model of the human colon

The aim of this study was to evaluate the effects of soy-based beverages manufactured with water-soluble soy extract, containing probiotic strains (Lactobacillus acidophilus LA-5 and Bifidobacterium longum BB-46) and/or acerola by-product (ABP) on pooled faecal microbiota obtained from lean and obese donors. Four fermented soy beverages (FSs) ("placebo" (FS-Pla), probiotic (FS-Pro), prebiotic (FS-Pre), and synbiotic (FS-Syn)) were subjected to in vitro digestion, followed by inoculation in the TIM-2 system, a dynamic in vitro model that mimics the conditions of the human colon. Short- and branched-chain fatty acids (SCFA and BCFA) and microbiota composition were determined. Upon colonic fermentation in the presence of the different FSs formulations, acetic and lactic acid production was higher than the control treatment for faecal microbiota from lean individuals (FMLI). Additionally, SCFA production by the FMLI was higher than for the faecal microbiota from obese individuals (FMOI). Bifidobacterium spp. and Lactobacillus spp. populations increased during simulated colonic fermentation in the presence of FS-Syn in the FMLI and FMOI. FS formulations also changed the composition of the FMOI, resulting in a profile more similar to the FMLI. The changes in the composition and the increase in SCFA production observed for the FMLI and FMOI during these in vitro fermentations suggest a potential modulation effect of these microbiotas by the consumption of functional FSs. KEY POINTS: • Soy beverages increased Bifidobacterium abundance in microbiota from obese individuals. • The synbiotic beverage increased Bifidobacterium abundance in microbiota from lean individuals. • The synbiotic beverage changed the microbiota from obese individuals, approaching the lean profiles.

Effects of soybean oligosaccharide, stachyose, and raffinose on growth performance and cecal microbiota in broiler chickens

This study was conducted to examine the effects of soybean oligosaccharide, stachyose, and raffinose on growth performance and cecal microbiota in broiler chickens. Three-hundred 1-day-old Arbor Acres broiler chickens were randomly assigned to five dietary treatments: a basal diet (control diet); diets supplemented with soybean oligosaccharide, stachyose, or raffinose at levels of 0.6% total sugar content; and diet with soybean meals (positive control). Results showed that feed-to-gain ratio (F/G) was improved (p < 0.05) in broiler chickens that received stachyose, but not raffinose, while addition of soybean oligosaccharide to the diet significantly (p < 0.05) resulted in decreases in the average daily feed intake (ADFI) and average daily gain (ADG). Supplementation with soybean oligosaccharide, stachyose, or raffinose had a positive effect (p < 0.05) on the nutrient digestibility, but not on the blood immune parameters (p > 0.05). The results of the gene sequencing indicated that, at the family level, Ruminococcaceae, Lachnospiraceae, and Lactobacillaceae were comparatively present in all the treatments but the cecal microbial composition was changed after dietary addition of different oligosaccharides. Our study had led to a greater understanding of prebiotic effects of these oligosaccharides on growth and intestinal health.

Probiotic low-fat fermented goat milk with passion fruit by-product: In vitro effect on obese individuals' microbiota and on metabolites production

This study aimed to evaluate the impact of a two-week treatment period with probiotic low-fat fermented goat milk by Lactobacillus casei Lc-1, supplemented with passion fruit by-product (1%), on the modulation of gut microbiota from obese individuals using the Simulator of Human Intestinal Microbial Ecosystem (SHIME) system. The effects were carried out through the study of gut microbiota composition, using 16S rRNA next generation sequencing, quantification of short-chain fatty acids (SCFA) and ammonium ions. The microbiota composition changed across three vessels representing the colon regions, because of fermented milk treatment. Fermented goat milk administration caused a reduction of bacteria belonging to genera Prevotella, Megamonas and Succinivibrio, which can produce SCFA, and an increase of Lactobacillus and Bifidobacterium genera in all simulated colon regions. There was no effect on SCFA and on ammonium ions concentration during treatment period. Fermented milk shifted the obese donors' microbiota without changing metabolites production. It happens, possibly, due to a balance in abundances among bacterial genera that can produce or not SCFA, and among bacterial genera with high or low proteolytic activity. Our outcomes help to clarify the effects of the ingestion of a probiotic low-fat fermented goat milk product on colon microbiota composition.

Detection and isolation of the typical gut indigenous bacteria from ddY mice fed a casein-beef tallow-based or egg yolk-based diet

The effects of whole egg on the cecal microbiome of ddY mice has been reported. To investigate the existence of susceptible indigenous bacteria (SIB) to egg yolks (EY), mice were fed a diet containing either 20% (w/w) milk casein and 17% beef tallow (CT) or 12% milk casein and 27% EY for 14 days, and then, the cecal microbiome was analyzed by 16S rRNA (V4) amplicon sequencing. To isolate the typical species in each diet group, culture-dependent viable bacterial counts were determined on Blood Liver (BL) and Gifu Anaerobic Medium (GAM) agar plates. The amplicon sequencing analysis revealed typical CT-SIB, such as Lachnospiraceae-like bacteria, and EY-SIB, such as Allobaculum-, Lactobacillus murinus-, and Bacteroides vulgatus-like bacteria. Two of the detected SIB species, L. murinus- and B. vulgatus-like bacteria, were successfully isolated from the BL and GAM agar plates and defined using a 16S rDNA BLAST search. PRACTICAL APPLICATIONS: The SIB defined in the CT and EY groups might have some effects on the nutritional and functional chemical compounds in the milk casein, beef tallow, and/or EY. Analysis of its functional properties of the isolates might develop the new and unique probiotic strains.

Gut microbiota and short chain fatty acid composition as affected by legume type and processing methods as assessed by simulated in vitro digestion assays

This study's objective was to investigate how legume type and processing method affected digestibility, and subsequent gut microbiota and short chain fatty acid (SCFA) formation. After autoclaving and germinating-cooking, pinto bean and soybean were subjected to in vitro digestion. The digestion residues were fractionated into soluble and insoluble fiber, and fermented by microbiota from pig feces. Results showed the in vitro digestibility was affected significantly by processing method and legume type. Autoclaving resulted in higher digestibility. The in-vitro digested bean residues caused a rapid pH decrease in the first 12 h during the fermentation with pig feces, and a significant increse in the formation of SCFAs. A positive modulation of the gut microbiota by the in-vitro digested bean residues was observed. Prevotella copri and Bacteroides vulgatus exhibited the highest relative abundance in the treatments with germinated bean's soluble residues. Phascolarctobacterium succinatutens was increased by the insoluble residues.

Whole Food–Based Approaches to Modulating Gut Microbiota and Associated Diseases

Intake of whole foods, such as fruits and vegetables, may confer health benefits to the host. The beneficial effects of fruits and vegetables were mainly attributed to their richness in polyphenols and microbiota-accessible carbohydrates (MACs). Components in fruits and vegetables modulate composition and associated functions of the gut microbiota, whereas gut microbiota can transform components in fruits and vegetables to produce metabolites that are bioactive and important for health. The progression of multiple diseases, such as obesity and inflammatory bowel disease, is associated with diet and gut microbiota. Although the exact causality between these diseases and specific members of gut microbiota has not been well characterized, accumulating evidence supported the role of fruits and vegetables in modulating gut microbiota and decreasing the risks of microbiota-associated diseases. This review summarizes the latest findings on the effects of whole fruits and vegetables on gut microbiota and associated diseases.

Typical indigenous bacteria in the cecum of ddY mice fed a casein-beef tallow diet or whole-egg diet

With the aim to prove the existence of food ingredient-susceptible indigenous bacteria (SIBs) in the gut, the gut microbiota of ddY mice fed a diet containing 20% milk casein and 17% beef tallow (CT diet) or 40% whole-egg powder (Egg diet) for 14 days were analyzed by 16S ribosomal RNA gene (V4) amplicon sequencing. At the genus level, abundance levels of Desulfovibrionaceae sp., Oscillospira, and Bacteroides were high in mice fed the CT diet. At the operational taxonomic unit level, Bacteroides acidifaciens- and Bacteroides caecimuris-like bacteria were highly abundant in mice fed the CT diet. Faecalibaculum rodentium- and Allobaculum stercoricanis-like bacteria were highly abundant in the mice fed the Egg diet. These sets of taxa were assumed to be estimates of casein-tallow SIBs and egg SIBs, respectively, in the gut microbiome. Among the SIBs, B. caecimuris and F. rodentium could be isolated using blood and liver agar. PRACTICAL APPLICATIONS: B. caecimuris and F. rodentium are regarded as casein-tallow and/or egg SIBs in mice. It is possible to demonstrate functionality with orally administered food ingredients. Isolation and application of human or livestock SIB is considered promising for the development of new probiotics and functional foods.

Effect of rice bran fermented with Saccharomyces cerevisiae and Lactobacillus plantarum on gut microbiome of mice fed high-sucrose diet

To clarify the effect of rice bran (RB) and fermented RB (FRB) in a high-sucrose and low-dietary fibre diet on the gut microbiome, the in vitro bile acid-lowering capacity and caecal microbiota of ICR mice fed with 20% RB or FRB diets for two weeks were determined. The caecal microbiome was analysed by 16S rRNA gene amplicon sequencing. The in vitro bile acid-lowering capacity was high for FRB. In mouse experiments, triacylglycerol and total cholesterol were generally lower with FRB, although the faecal frequency was highest in mice fed with RB. The Shannon-Wiener and Simpson's indices for alpha-diversity in the microbiome of mice fed with RB and FRB, were higher than mice fed the control diet. At the phylum level in the caecal microbiome, Firmicutes and Bacteroidetes were high with FRB and RB, respectively. At the operational taxonomic unit level, some bacterial groups related to diabetes and gut toxicity, such as Lachnospiraceae and Enterorhabdus mucosicola, were high for RB but not for FRB diets. These results suggest that FRB, rather than RB, intake improve the intestinal environment and blood lipid condition.

Glycation of fish protein impacts its fermentation metabolites and gut microbiota during in vitro human colonic fermentation

The aim of this study was to investigate the fermentation properties of fish protein (FP) glycated with glucose at two different heating time (24 h and 48 h, 50 °C, GFP24 and GFP48), using an in vitro batch fermentation model of human distal colon. The heated fish protein in absent of glucose was also as controls. The lower glycation extent of fish protein, with a lower browning intensity and bound sugar, enhanced the production of acetate and propionate. The formation of indole and ammonia was inhibited by the glycation of fish protein, but less affected by its glycation extent. Compared to FP, the glycation of fish protein significantly increased (p < .05) the relative abundance of genera Lactococcus for GFP24 (47%) and GFP48 (71%), whereas decreased dominant genera Bacteroides for GFP24 (32%) and GFP48 (23%). Compared to GFP24, GFP48 indicated significantly higher relative abundance of Holdemania, Streptococcus, Enterococcus and Lactobacillus, and lower amounts of Parabacteroides (p < .05). In the meantime, the heated treatments in the absent of glucose resulted in the increase of some genera Dialister, Arobacter, Clostridium_sensu_stricto_1, Phascolarctobacterium and Veillonella, and also ammonia production. Furthermore, the correlation analysis confirmed that the glycation of fish protein for the decrease of ammonia and indole production was associated with the changes of some proteolytic bacteria genera, including Bacteroides, Dialister and Parabacteroides. Thus, the glycated fish protein rich in Amadori products greatly change the profiles of fermentation metabolite and gut microbiota, and these changes can have a potential impact on host health.

Does Modification of the Large Intestinal Microbiome Contribute to the Anti-Inflammatory Activity of Fermentable Fiber?

Fiber is an inadequately understood and insufficiently consumed nutrient. This review examines the possible causal relation between fiber-induced microbiome changes and the anti-inflammatory activity of fiber. To demonstrate the dominant role of fermentable plant fiber in shaping the intestinal microbiome, animal and human fiber-feeding studies are reviewed. Using culture-, PCR-, and sequencing-based microbial analyses, a higher prevalence of Bifidobacterium and Lactobacillus genera was observed from the feeding of different types of fermentable fiber. This finding was reported in studies performed on several host species including human. Health conditions and medications that are linked to intestinal microbial alterations likely also change the nutrient environment of the large intestine. The unique gene clusters of Bifidobacterium and Lactobacillus that enable the catabolism of plant glycans and the ability of Bifidobacterium and Lactobacillus to reduce the colonization of proteobacteria probably contribute to their prevalence in a fiber-rich intestinal environment. The fiber-induced microbiome changes could contribute to the anti-inflammatory activity of fiber. Although most studies did not measure fecal microbial density or total daily fecal microbial output (colon microbial load), limited evidence suggests that the increase in intestinal commensal microbial load plays an important role in the anti-inflammatory activity of fiber. Various probiotic supplements, including Bifidobacterium and Lactobacillus, showed anti-inflammatory activity only in the presence of fiber, which promoted microbial growth as indicated by increasing plasma short-chain fatty acids. Probiotics alone or pure fiber administered under sterile conditions showed no anti-inflammatory activity. The potential mechanisms that could mediate the anti-inflammatory effect of common microbial metabolites are reviewed, but more in vivo trials are needed. Future studies including simultaneous microbial composition and load measurements are also important.