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Partially hydrolyzed guar gums (PHGGs) are prebiotic soluble dietary fibers. High molecular-weight PHGGs have rapid fermentation and high short-chain fatty acid (SCFA) productivity rates, compared to low molecular-weight PHGGs. Therefore, low molecular-weight PHGGs may have less pronounced prebiotic effects than high molecular-weight PHGGs. However, the effects of PHGGs of different molecular weights on the human intestinal microbiota, as well as their fermentation ability and prebiotic effects, have not been investigated. The aim of this study was to evaluate the effects of two PHGGs of different molecular weights, Sunfiber-R (SF-R; 20 kDa) and Sunfiber-V (SF-V; 5 kDa), on human colonic microbiota and SCFA production. A human intestinal in vitro fermentation model was operated by fecal samples with and without the PHGGs. The addition of 0.2% SF-R or SF-V increased the relative abundance of Bacteroides spp., especially that of Bacteroides uniformis. This increase corresponded to a significant (p = 0.030) and non-significant (p = 0.073) increase in propionate production in response to SF-R and SF-V addition, respectively. Both fibers increased the relative abundance of Faecalibacterium and stimulated an increase in the abundance of unclassified Lachnospiraceae and Bifidobacterium. In conclusion, the low molecular-weight PHGG exerted prebiotic effects on human colonic microbiota to increase SCFA production and bacteria that are beneficial to human health in a manner similar to that of the high molecular-weight forms of PHGG. [Display omitted] • We assessed the potential effects of two types of partially hydrolyzed guar gum (PHGG). • The addition of 0.2% SF-R and SF-V increased the relative abundance of Bacteroides members and propionate production. • Sunfiber-R significantly increased propionate production. • Sunfiber-V also increased propionate production, but not significantly. • Our study shows the potential of PHGGs to increase the abundance of beneficial gut bacteria and the production of SCFAs. [ABSTRACT FROM AUTHOR]

The human colonic microbiota plays an important role in the food digestion process and has a key role in maintaining health status. This community of microbes is inter-individually different due to several factors that modulate its composition. Among them, diet is one of the most relevant, which, in turn, is affected by environmental, economic, and cultural considerations. These pieces of evidence have promoted the study of the influence of diet on gut microbiota and the development of in vitro models that simulate the colonic digestion of foods. This narrative review aims to present a technical approach of the in vitro gut models available to evaluate the impact of diet on human colonic microbiota. A description and comments on the main characteristics, parameters, applicability, faecal inoculum preparation, and analytical tools are made. Despite the progress of in vitro colonic digestion models and metaomic applicability in this research field, there are still some challenges to face due to the lack of a consensus on the methodologies to conduct in vitro colonic digestions and the need to integrate the metaomic data to fully understand the influence of food in human colonic microbiota. [ABSTRACT FROM AUTHOR]

Summary: Prebiotics are known for their health benefits to man, including reducing cardiovascular disease and improving gut health. This review takes a critical assessment of the impact of dietary fibres and prebiotics on the gastrointestinal microbiota in vitro. The roles of colonic organisms, slow fermentation of prebiotics, production of high butyric and propionic acids and positive modulation of the host health were taken into cognizance. Also, the short‐chain fatty acids (SCFAs) molecular signalling mechanisms associated with their prebiotic substrate structural conformations and the phenotypic responses related to the gut microbes composition were discussed. Furthermore, common dietary fibres such as resistant starch, pectin, hemicelluloses, β‐glucan and fructan in context of their prebiotic potentials for human health were also explained. Finally, the in vitro human colonic fermentation depends on prebiotic type and its physicochemical characteristics, which will then affect the rate of fermentation, selectivity of micro‐organisms to multiply, and SCFAs concentrations and compositions. [ABSTRACT FROM AUTHOR]

Several investigations have elucidated the chemistry of prebiotics based on their fermentation by the colonic microbes, which release metabolites that are often implicated in host's gut and whole body health. The present study aims at providing a preview of prebiotics and their interactions with the colonic microbiota for a slow fermentation in vitro. The metabolites produced, mainly short chain fatty acids (SCFA), their chemistry, interactions with prebiotic structural mechanisms, and beneficial impacts on the host were also reported. The present review further considers the clinical relevance of the SCFAs produced. It was deduced that the physicochemical properties of prebiotics would influence their colonic fermentation rate, microbial choice, and growth as well as SCFA type and ratios. This will in turn be of utmost clinical significance. Key points: • Prebiotics affect the composition of gut microorganisms. • The chemistry of short chain fatty acids are described. • Microbial and clinical applications of SCFAs were provided. [ABSTRACT FROM AUTHOR]

The human colonic microbiota plays an important role in the food digestion process and has a key role in maintaining health status. This community of microbes is inter-individually different due to several factors that modulate its composition. Among them, diet is one of the most relevant, which, in turn, is affected by environmental, economic, and cultural considerations. These pieces of evidence have promoted the study of the influence of diet on gut microbiota and the development of in vitro models that simulate the colonic digestion of foods. This narrative review aims to present a technical approach of the in vitro gut models available to evaluate the impact of diet on human colonic microbiota. A description and comments on the main characteristics, parameters, applicability, faecal inoculum preparation, and analytical tools are made. Despite the progress of in vitro colonic digestion models and metaomic applicability in this research field, there are still some challenges to face due to the lack of a consensus on the methodologies to conduct in vitro colonic digestions and the need to integrate the metaomic data to fully understand the influence of food in human colonic microbiota.

To evaluate the potential antibiotic resistance capability of cultured human colonic microbiota as a whole system when residual antibiotics enter the human intestine, the combination of viable cell counting and denaturing gradient gel electrophoresis (DGGE) method was used to study effects of the enrofloxacin (ENR) residue on the microbial diversity, antibiotic resistance, and anti-colonization capability in a human chemostat model. The results indicated that the ENR enhanced the microbial antibiotic resistance to the ciprofloxacin (CI), and a dose-dependent effect was observed. When exposed to 1.25 μg/mL ENR, the growth of the tested bacteria (e.g., total aerobic bacteria, total anaerobic bacteria, Lactobacillus, Enterococci, Escherichia coli, Bacteroides fragilis) received little change, while the microbial diversity in this group was totally changed; In 12.5- and 125-μg/mL ENR group, the quantities and microbial diversity received a dramatic change compared to their no drug stage, while the addition of the cultured human colonic microbiota to the probiotic group did enhance the colonization resistance (CR) of the cultured microbiota to Candida albicans SC5314, indicating its potential beneficial effect on human intestinal healthy and anti-infection capability. [ABSTRACT FROM AUTHOR]

Abstract: 7-Hydroxy-5-methyl-3-phenyl-6,7,8,9-tetrahydropyrido[3′,2′:4,5]imidazo[1,2-a]pyrimidin-5-ium chloride (PhIP-M1) is a newly identified intestinal microbial metabolite from the food carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Although the mutagenic potential of the endogenous N-hydroxy PhIP derivate has been reported, the risks associated with PhIP-M1 have not yet been explored. In this work, the cytotoxic and genotoxic effects originating from PhIP-M1 were assessed in the epithelial intestinal Caco-2 cell line. PhIP-M1 significantly decreased in a time- and dose-dependent manner mitochondrial dehydrogenase activity and protein synthesis, with IC50 values of, respectively, 180±39.4 and 173±20.3μM after 24h, and 33.8±3.5 and 37.3±10.9μM after 72h. Apoptosis within the concentration ranges of cytotoxicity was confirmed by morphological examination, DAPI nuclear staining and annexin V staining. PhIP-M1 provoked cell cycle arrest, characterized by a significant increase in the number of nucleoids in the G2/M phase. A dose-dependent increase in DNA damage, as quantified by the alkaline comet assay, was observed after 3h in the 50–200μM range. Because these PhIP-M1-induced genomic and cellular events may contribute to the carcinogenicity of PhIP, the potency of the colon microbiota to bioactivate PhIP must be included in future risk assessments. [Copyright &y& Elsevier]

Isothiocyanates have been implicated in the cancer-protective effects of brassica vegetables. When cabbage is consumed, sinigrin is hydrolysed by plant or microbial myrosinase partly to allyl isothiocyanate (AITC), which is mainly excreted as N-acetylcysteine conjugates (NAC) of AITC in urine. The effect of cooking cabbage on the excretion of NAC of AITC, and glutathione-S-transferase (GST) and uridine 5???-diphospho-glucuronosyl transferase (UGT) activity in rat liver and colon was investigated. Germ-free (GF) and human faecal microbiota-associated (HFM) rats were fed a control diet containing 20??% raw, lightly cooked, or fully cooked cabbage for 14??d. When plant myrosinase was present, excretion of NAC of AITC/24??h was increased by 1??4 and 2??5 times by the additional presence of microbial myrosinase after consumption of raw and lightly cooked cabbage respectively. When plant myrosinase was absent, as after consumption of fully cooked cabbage, excretion of the AITC conjugate was almost zero in GF and HFM rats. None of the cabbage diets modified hepatic GST activity. When microbiota was absent, colonic GST was 1??3-fold higher after fully cooked cabbage, and hepatic UGT was increased by 1??4???1??8-fold after all cabbage diets, compared with the control feed. There were no differences in GST or UGT following cabbage consumption when microbiota was present. It is possible that other constituents of cabbage, rather than metabolites of glucosinolates per se, may be responsible for changes in phase 2 enzyme activity. The main effect of cooking cabbage and altering colonic microbiota was on excretion of NAC of AITC. [ABSTRACT FROM PUBLISHER]

Butyrate producers constitute an important bacterial group in the human large intestine. Butyryl-CoA is formed from two molecules of acetyl-CoA in a process resembling β-oxidation in reverse. Three different arrangements of the six genes coding for this pathway have been found in low mol% G+C-content Gram-positive human colonic bacteria using DNA sequencing and degenerate PCR. Gene arrangements were strongly conserved within phylogenetic groups defined by 16S rRNA gene sequence relationships. In the case of one of the genes, encoding β-hydroxybutyryl-CoA dehydrogenase, however, sequence relationships were strongly suggestive of horizontal gene transfer between lineages. The newly identified gene for butyryl-CoA CoA-transferase, which performs the final step in butyrate formation in most known human colonic bacteria, was not closely linked to these central pathway genes. [ABSTRACT FROM AUTHOR]

Abstract: Various molecular–biological approaches using the 16S rRNA gene sequence have been used for the analysis of human colonic microbiota. Terminal- restriction fragment length polymorphism (T-RFLP) analysis is suitable for a rapid comparison of complex bacterial communities. Terminal-restriction fragment (T-RF) length can be calculated from a known sequence, thus one can predict bacterial species on the basis of their T-RF length by this analysis. The aim of this study was to build a phylogenetic assignment database for T-RFLP analysis of human colonic microbiota (PAD-HCM), and to demonstrate the effectiveness of PAD-HCM compared with the results of 16S rRNA gene clone library analysis. PAD-HCM was completed to include 342 sequence data obtained using four restriction enzymes. Approximately 80% of the total clones detected by 16S rRNA gene clone library analysis were the same bacterial species or phylotypes as those assigned from T-RF using PAD-HCM. Moreover, large T-RFs consisted of common species or phylotypes detected by both analytical methods. All pseudo-T-RFs identified by mung bean nuclease digestion could not be assigned to a bacterial species or phylotype, and this finding shows that pseudo-T-RFs can also be predicted using PAD-HCM. We conclude that PAD-HCM built in this study enables the prediction of T-RFs at the species level including difficult-to-culture bacteria, and that it is very useful for the T-RFLP analysis of human colonic microbiota. [Copyright &y& Elsevier]