In vitro assessment of the bioaccessibility of brominated flame retardants in indoor dust using a colon extended model of the human gastrointestinal tract

An in vitro colon extended physiologically based extraction test (CEPBET) which incorporates human gastrointestinal tract (GIT) parameters (including pH and chemistry, solid-to-fluid ratio, mixing and emptying rates) was applied for the first time to study the bioaccessibility of brominated flame retardants (BFRs) from the 3 main GIT compartments (stomach, small intestine and colon) following ingestion of indoor dust. Results revealed the bioaccessibility of γ-HBCD (72%) was less than that for α- and β-isomers (92% and 80% respectively) which may be attributed to the lower aqueous solubility of the γ-isomer (2 μg L−1) compared to the α- and β-isomers (45 and 15 μg L−1 respectively). No significant change in the enantiomeric fractions of HBCDs was observed in any of the studied samples. However, this does not completely exclude the possibility of in vivo enantioselective absorption of HBCDs, as the GIT cell lining and bacterial flora – which may act enantioselectively – are not included in the current CE-PBET model. While TBBP-A was almost completely (94%) bioaccessible, BDE-209 was the least (14%) bioaccessible of the studied BFRs. Bioaccessibility of tri-hepta BDEs ranged from 32–58%. No decrease in the bioaccessibility with increasing level of bromination was observed in the studied PBDEs.

Survivability of a probiotic Lactobacillus casei in the gastrointestinal tract of healthy human volunteers and its impact on the faecal microflora

Aim: The aim of this study was to measure the gastrointestinal survival of Lactobacillus casei and its impact on the gut microflora in healthy human volunteers. Methods and Results: Twenty healthy volunteers took part in a double-blind placebo-controlled probiotic feeding study (10 fed probiotic, 10 fed placebo). The probiotic was delivered in two 65 ml aliquots of fermented milk drink (FMD) daily for 21 days at a dose of 8.6 +/- 0.1 Log(10)Lact. casei CFU ml(-1) FMD. Faecal samples were collected before, during and after FMD or placebo consumption, and important groups of faecal bacteria enumerated by fluorescent in situ hybridization (FISH) using oligonucleotide probes targeting the 16S rRNA. The fed Lact. casei was enumerated using selective nutrient agar and colony identity confirmed by pulsed field gel electrophoresis. Seven days after ingestion of FMD, the Lact. casei was recovered from faecal samples taken from the active treatment group at 7.1 +/- 0.4 Log(10) CFU g(-1) faeces (mean +/- SD, n = 9) and numbers were maintained at this level until day 21. Lact. casei persisted in six volunteers until day 28 at 5.0 +/- 0.9 Log(10) CFU g(-1) faeces (mean +/- SD, n = 6). Numbers of faecal lactobacilli increased significantly upon FMD ingestion. In addition, the numbers of bifidobacteria were higher on days 7 and 21 than on days 0 and 28 in both FMD fed and placebo fed groups. Consumption of Lact. casei had little discernible effect on other bacterial groups enumerated. Conclusions: Daily consumption of FMD enabled a probiotic Lact. casei strain to be maintained in the gastrointestinal tract of volunteers at a stable relatively high population level during the probiotic feeding period. Significance and Impact of the Study: The study has confirmed that this probiotic version of Lact. casei survives well within the human gastrointestinal tract.

Bacterial biofilms in the human gastrointestinal tract

Microbial biofilms were first described in 1936 and subsequent research has unveiled their ubiquity and physiological distinction from free-living (planktonic) microorganisms. In light of their emerging significance this review examines the bacterial biofilms within the human gastrointestinal tract. Attention is paid to the nature of these mucosally- associated populations, focusing on the protected environment afforded by the continual secretion of mucus by host epithelial cells. It also examines the attributes possessed by various bacterial species that facilitate habitation of this microenvironment. Additionally, contrasts are drawn between planktonic bacteria of the lumen and sessile (biofilm) bacteria growing in close association with host cells and food particles. In particular the different fermentation profiles exhibited by these two fractions are discussed. The potential role of these communities in host health and disease, as well as the stabilisation of the lumenal population, is also considered. Reference is made to the state of mutualism that exists between these little understood populations and the host epithelia, thus highlighting their ecological significance in terms of gastrointestinal health.

Gastrointestinal tract: intestinal fatty acid metabolism and implications for health

Short-chain fatty acids (SCFA) are formed from the fermentation of sugars by intestinal bacteria. Acetate is the most abundant SCFA, with lower amounts of propionate and butyrate formed. Propionate and butyrate are also formed from the products of carbohydrate fermentation by other bacteria, for example from lactate and acetate. SCFA play a role in regulating transit of digesta through the intestine, and butyrate formation is thought to be beneficial to health because butyrate decreases the risk of colon cancer. Major butyrate-producing species are among the most abundant present in the colon, including Roseburia and Faecalibacterium spp. Metabolism of longer-chain fatty acids occurs mainly by hydration or hydrogenation of unsaturated fatty acids. Hydroxystearic acids are formed in the intestine, particularly under disease conditions. Metabolism of linoleic acid results in the formation of conjugated linoleic acids (CLA) by several species, including Roseburia hominis and Roseburia inulinovorans. Enhancement of intestinal CLA formation, possibly using probiotics, may be useful in preventing or treating inflammatory bowel disease.

The fate of olive oil polyphenols in the gastrointestinal tract: implications of gastric and colonic microflora-dependent biotransformation

We have conducted a detailed investigation into the absorption, metabolism and microflora-dependent transformation of hydroxytyrosol ( HT), tyrosol (TYR) and their conjugated forms, such as oleuropein (OL). Conjugated forms underwent rapid hydrolysis under gastric conditions, resulting in significant increases in the amount of free HT and TYR entering the small intestine. Both HT and TYR transferred across human Caco-2 cell monolayers and rat segments of jejunum and ileum and were subject to classic phase I/II biotransformation. The major metabolites identified were an O-methylated derivative of HT, glucuronides of HT and TYR and a novel glutathionylated conjugate of HT. In contrast, there was no absorption of OL in either model. However, OL was rapidly degraded by the colonic microflora resulting in the formation of HT. Our study provides additional information regarding the breakdown of complex olive oil polyphenols in the GI tract, in particular the stomach and the large intestine.

Metabolism of tea flavonoids in the gastrointestinal tract

There is considerable interest in the bioavailability of flavan-3-ols such as tea catechins and their bioactivity in vivo. Although flavanols such as catechin and epicatechin have long been characterized as powerful antioxidants in vitro, evidence suggests that these compounds undergo significant metabolism and conjugation during absorption in the small intestine and in the colon. In the small intestine these modifications lead primarily to the formation of glucuronide conjugates that are more polar than the parent flavanol and are marked for renal excretion. Other phase II processes lead to the production of O-methylated forms that have reduced antioxidant potential via the methylation of the B-ring catechol. Significant modification of flavanols also occurs in the colon where the resident microflora degrade them to smaller phenolic acids, some of which may be absorbed. Cell, animal and human studies have confirmed such metabolism by the detection of flavanol metabolites in the circulation and tissues. This review will highlight the major sites of flavanol metabolism in the gastrointestinal tract and the processes that give rise to potential bioactive forms of flavan-3-ols in vivo.

Bacillus subtilis spores germinate in the chicken gastrointestinal tract

A number of poultry probiotics contain bacterial spores. In this study, orally administered spores of Bacillus subtilis germinated in the gastrointestinal (GI) tracts of chicks. Furthermore, 20 h after spores were administered, vegetative cells outnumbered spores throughout the GI tract. This demonstrates that spore-based probiotics may function in this host through metabolically active mechanisms.

Screening for Bacillus isolates in the broiler gastrointestinal tract

Spores from a number of different Bacillus species are currently being used as human and animal probiotics, although their mechanisms of action remain poorly understood. Here we describe the isolation of 237 presumptive gut-associated Bacillus spp. isolates that were obtained by heat and ethanol treatment of fecal material from organically reared broilers followed by aerobic plating. Thirty-one representative isolates were characterized according to their morphological, physiological, and biochemical properties as well as partial 16S rRNA gene sequences and screening for the presence of plasmid DNA. The Bacillus species identified included B. subtilis, B. pumilus, B. licheniformis, B. clausii, B. megaterium, B. firmus, and species of the B. cereus group, whereas a number of our isolates could not be classified. Intrinsic properties of potential importance for survival in the gut that could be advantageous for spore-forming probiotics were further investigated for seven isolates belonging to five different species. All isolates sporulated efficiently in the laboratory, and the resulting spores were tolerant to simulated gastrointestinal tract conditions. They also exhibited antimicrobial activity against a broad spectrum of bacteria, including food spoilage and pathogenic organisms such as Bacillus spp., Clostridium perfringens, Staphylococcus aureus, and Listeria monocytogenes. Importantly, the isolates were susceptible to most of the antibiotics tested, arguing that they would not act as donors for resistance determinants if introduced in the form of probiotic preparations. Together, our results suggest that some of the sporeformers isolated in this study have the potential to persist in or transiently associate with the complex gut ecosystem.

Localization of calcitonin receptor-like receptor (CLR) and receptor activity-modifying protein 1 (RAMP1) in human gastrointestinal tract

Calcitonin gene-related peptide (CGRP) exerts its diverse effects on vasodilation, nociception, secretion, and motor function through a heterodimeric receptor comprising of calcitonin receptor-like receptor (CLR) and receptor activity-modifying protein 1 (RAMP1). Despite the importance of CLR.RAMP1 in human disease, little is known about its distribution in the human gastrointestinal (GI) tract, where it participates in inflammation and pain. In this study, we determined that CLR and RAMP1 mRNAs are expressed in normal human stomach, ileum and colon by RT-PCR. We next characterized antibodies that we generated to rat CLR and RAMP1 in transfected HEK cells. Having characterized these antibodies in vitro, we then localized CLR-, RAMP1-, CGRP- and intermedin-immunoreactivity (IMD-IR) in various human GI segments. In the stomach, nerve bundles in the myenteric plexus and nerve fibers throughout the circular and longitudinal muscle had prominent CLR-IR. In the proximal colon and ileum, CLR was found in nerve varicosities of the myenteric plexus and surrounding submucosal neurons. Interestingly, CGRP expressing fibers did not co-localize, but were in close proximity to CLR. However, CLR and RAMP1, the two subunits of a functional CGRP receptor were clearly localized in myenteric plexus, where they may form functional cell-surface receptors. IMD, another member of calcitonin peptide family was also found in close proximity to CLR, and like CGRP, did not co-localize with either CLR or RAMP1 receptors. Thus, CGRP and IMD appear to be released locally, where they can mediate their effect on their receptors regulating diverse functions such as inflammation, pain and motility.

Protease-activated receptors: protease signaling in the gastrointestinal tract

Serine proteases from the circulation, inflammatory cells, digestive glands and microorganisms can signal to cells by cleaving protease-activated receptors (PARs), a family of four G-protein-coupled receptors. Proteases cleave PARs at specific sites to expose tethered ligand domains that bind to and activate the cleaved receptors. Despite this irreversible mechanism of activation, PAR signaling is tightly regulated to prevent the uncontrolled stimulation of cells. Although PARs are found in all organ systems, protease signaling is of particular interest in the gastrointestinal tract, where proteases regulate neurotransmission, secretion, motility, epithelial permeability and intestinal inflammation, and can thus contribute to disease.

Colonization, persistence, and tissue tropism of Escherichia coli O26 in conventionally reared weaned lambs

Escherichia coli O26 is recognized as an emerging pathogen associated with disease in both ruminants and humans. Compared to those of E. coli O157:117, the shedding pattern and location of E. coli O26 in the gastrointestinal tract (GIT) of ruminants are poorly understood. In the studies reported here, an stx-negative E. coli O26 strain of ovine origin was inoculated orally into 6-week-old lambs and the shedding pattern of the O26 strain was monitored by serial bacteriological examination of feces. The location of colonization in the GIT was examined at necropsy at two time points. The numbers of O26 organisms excreted in feces declined from approximately 10(7) to 10(4) CFU per gram of feces by day 7 and continued at this level for a further 3 weeks. Beyond day 30, excretion was from few animals, intermittent, and just above the detection limit. By day 38, all fecal samples were negative, but at necropsy, O26 organisms were recovered from the upper GIT, specifically the ileum. However, no attaching-effacing (AE) lesions were observed. To identify the location of E. coli O26 within the GIT early after inoculation, two lambs were examined postmortem, 4 days postinoculation. High numbers of O26 organisms were recovered from all GIT sites examined, and similar to 10(9) CFU were recovered from 1 gram of ileal tissue from one animal. Despite high numbers of O26 organisms, AE lesions were identified on the mucosa of the ascending colon of only one animal. These data indicate that E. coli O26 readily colonizes 6-week-old lambs, but the sparseness of AE lesions suggests that O26 is well adapted to this host, and mechanisms other than those dependent upon intimin may play a role in persistence.