Green fluorescent protein for detection of the probiotic microorganism Escherichia coli strain Nissle 1917 (EcN) in vivo

Towards Understanding Tumour Colonisation by Probiotic Bacterium E. coli Nissle 1917

The last decade has seen a rapid increase in studies utilising a genetically modified probiotic, Escherichia coli Nissle 1917 (EcN), as a chassis for cancer treatment and detection. This approach relies on the ability of EcN to home to and selectively colonise tumours over normal tissue, a characteristic common to some bacteria that is thought to result from the low-oxygen, nutrient-rich and immune-privileged niche the tumour provides. Pre-clinical studies have used genetically modified EcN to deliver therapeutic payloads that show efficacy in reducing tumour burden as a result of high-tumour and low off-target colonisation. Most recently, the EcN chassis has been expanded into an effective tumour-detection tool. These advances provide strong justification for the movement of genetically modified EcN into clinical oncology trials. What is currently unknown in the field is a deep mechanistic understanding of how EcN distributes to and localises within tumours. This review summarises the existing EcN literature, with the inclusion of research undertaken with other tumour-homing and pathogenic bacteria, to provide insights into possible mechanisms of EcN tumour homing for future validation. Understanding exactly how and why EcN colonises neoplastic tissue will inform the design and testing of the next generation of EcN chassis strains to address biosafety and containment concerns and optimise the detection and treatment of cancer.

Progress in methods for the detection of viable Escherichia coli

Escherichia coli (E. coli) is a prevalent enteric bacterium and a necessary organism to monitor for food safety and environmental purposes. Developing efficient and specific methods is critical for detecting and monitoring viable E. coli due to its high prevalence. Conventional culture methods are often laborious and time-consuming, and they offer limited capability in detecting potentially harmful viable but non-culturable E. coli in the tested sample, which highlights the need for improved approaches. Hence, there is a growing demand for accurate and sensitive methods to determine the presence of viable E. coli. This paper scrutinizes various methods for detecting viable E. coli, including culture-based methods, molecular methods that target DNAs and RNAs, bacteriophage-based methods, biosensors, and other emerging technologies. The review serves as a guide for researchers seeking additional methodological options and aiding in the development of rapid and precise assays. Moving forward, it is anticipated that methods for detecting E. coli will become more stable and robust, ultimately contributing significantly to the improvement of food safety and public health.

Advances in Escherichia coli Nissle 1917 as a customizable drug delivery system for disease treatment and diagnosis strategies

With the in-depth and comprehensive study of bacteria and their related ecosystems in the human body, bacterial-based drug delivery system has become an emerging biomimetic platform that can retain the innate biological functions. Benefiting from its good biocompatibility and ideal targeting ability as a biological carrier, Escherichia coli Nissle 1917 (ECN) has been focused on the treatment strategies of inflammatory bowel disease and tumor. The advantage of a bacterial carrier is that it can express exogenous protein while also acting as a natural capsule by releasing drug slowly as a result of its own colonization impact. In order to survive in harsh environments such as the digestive tract and tumor microenvironment, ECN can be modified or genetically engineered to enhance its function and host adaptability. The adoption of ECN carries or expresses drugs which are essential for accurate diagnosis and treatment. This review briefly describes the properties of ECN, the relationship between ECN and inflammation and tumor, and the strategy of using surface modification and genetic engineering to modify ECN as a delivery carrier for disease treatment.

Escherichiacoli Nissle 1917 as a Novel Microrobot for Tumor-Targeted Imaging and Therapy

Highly efficient drug delivery systems with excellent tumor selectivity and minimal toxicity to normal tissues remain challenging for tumor treatment. Although great effort has been made to prolong the blood circulation and improve the delivery efficiency to tumor sites, nanomedicines are rarely approved for clinical application. Bacteria have the inherent properties of homing to solid tumors, presenting themselves as promising drug delivery systems. Escherichia coli Nissle 1917 (EcN) is a commonly used probiotic in clinical practice. Its facultative anaerobic property drives it to selectively colonize in the hypoxic area of the tumor for survival and reproduction. EcN can be engineered as a bacteria-based microrobot for molecular imaging, drug delivery, and gene delivery. This review summarizes the progress in EcN-mediated tumor imaging and therapy and discusses the prospects and challenges for its clinical application. EcN provides a new idea as a delivery vehicle and will be a powerful weapon against cancer.

A novel standalone microfluidic device for local control of oxygen tension for intestinal-bacteria interactions

The intestinal environment is unique because it supports the intestinal epithelial cells under a normal oxygen environment and the microbiota under an anoxic environment. Due to importance of understanding the interactions between the epithelium and the microbiota, there is a strong need for developing representative and simple experimental models. Current approaches do not capture the partitioned oxygen environment, require external anaerobic chambers, or are complex. Another major limitation is that with the solutions that can mimic this oxygen environment, the oxygenation level of the epithelial cells is not known, raising the question whether the cells are hypoxic or not. We report standalone microfluidic devices that form a partitioned oxygen environment without the use of an external anaerobic chamber or oxygen scavengers to coculture intestinal epithelial and bacterial cells. By changing the thickness of the device cover, the oxygen tension in the chamber was modulated. We verified the oxygen levels using several tests: microscale oxygen sensitive sensors which were integrated within the devices, immunostaining of Caco-2 cells to determine hypoxia levels, and genetically encoded bacteria to visualize the growth. Collectively, these methods monitored oxygen concentrations in the devices more comprehensively than previous reports and allowed for control of oxygen tension to match the requirements of both intestinal cells and anaerobic bacteria. Our experimental model is supported by the mathematical model that considered diffusion of oxygen into the top chamber. This allowed us to experimentally determine the oxygen consumption rate of the intestinal epithelial cells under perfusion.

Plasmid Vectors for in Vivo Selection-Free Use with the Probiotic E. coli Nissle 1917

Escherichia coli Nissle 1917 (EcN) is a probiotic bacterium, commonly employed to treat certain gastrointestinal disorders. It is fast emerging as an important target for the development of therapeutic engineered bacteria, benefiting from the wealth of knowledge of E. coli biology and ease of manipulation. Bacterial synthetic biology projects commonly utilize engineered plasmid vectors, which are simple to engineer and can reliably achieve high levels of protein expression. However, plasmids typically require antibiotics for maintenance, and the administration of an antibiotic is often incompatible with in vivo experimentation or treatment. EcN natively contains plasmids pMUT1 and pMUT2, which have no known function but are stable within the bacteria. Here, we describe the development of the pMUT plasmids into a robust platform for engineering EcN for in vivo experimentation, alongside a CRISPR-Cas9 system to remove the native plasmids. We systematically engineered both pMUT plasmids to contain selection markers, fluorescent markers, temperature sensitive expression, and curli secretion systems to export a customizable functional material into the extracellular space. We then demonstrate that the engineered plasmids were maintained in bacteria as the engineered bacteria pass through the mouse GI tract without selection, and that the secretion system remains functional, exporting functionalized curli proteins into the gut. Our plasmid system presents a platform for the rapid development of therapeutic EcN bacteria.

Microbes as Biosensors

The ability to detect disease early and deliver precision therapy would be transformative for the treatment of human illnesses. To achieve these goals, biosensors that can pinpoint when and where diseases emerge are needed. Rapid advances in synthetic biology are enabling us to exploit the information-processing abilities of living cells to diagnose disease and then treat it in a controlled fashion. For example, living sensors could be designed to precisely sense disease biomarkers, such as by-products of inflammation, and to respond by delivering targeted therapeutics in situ. Here, we provide an overview of ongoing efforts in microbial biosensor design, highlight translational opportunities, and discuss challenges for enabling sense-and-respond precision medicines.

Beneficial effects of Lactobacillus reuteri 6475 on bone density in male mice is dependent on lymphocytes

Oral treatment with probiotic bacteria has been shown to prevent bone loss in multiple models of osteoporosis. In previous studies we demonstrated that oral administration of Lactobacillus reuteri in healthy male mice increases bone density. The host and bacterial mechanisms of these effects however are not well understood. The objective of this study was to understand the role of lymphocytes in mediating the beneficial effects of L. reuteri on bone health in male mice. We administered L. reuteri in drinking water for 4 weeks to wild type or Rag knockout (lack mature T and B lymphocytes) male mice. While L. reuteri treatment increased bone density in wild type, no significant increases were seen in Rag knockout mice, suggesting that lymphocytes are critical for mediating the beneficial effects of L. reuteri on bone density. To understand the effect of L. reuteri on lymphocytes in the intestinal tissues, we isolated mesenteric lymph node (MLN) from naïve wild type mice. In ex vivo studies using whole mesenteric lymph node (MLN) as well as CD3+ T-cells, we demonstrate that live L. reuteri and its secreted factors have concentration-dependent effects on the expression of cytokines, including anti-inflammatory cytokine IL-10. Fractionation studies identified that the active component of L. reuteri is likely water soluble and small in size (<3 kDa) and its effects on lymphocytes are negatively regulated by a RIP2 inhibitor, suggesting a role for NOD signaling. Finally, we show that T-cells from MLNs treated with L. reuteri supernatants, secrete factors that enhance osterix (transcription factor involved in osteoblast differentiation) expression in MC3T3-E1 osteoblasts. Together, these data suggest that L. reuteri secreted factors regulate T-lymphocytes which play an important role in mediating the beneficial effects of L. reuteri on bone density.

Emerging Frontiers in Microbiome Engineering

The gut microbiome has a significant impact on health and disease and can actively contribute to obesity, diabetes, inflammatory bowel disease, cardiovascular disease, and neurological disorders. We do not yet have the necessary tools to fine-tune the microbial communities that constitute the microbiome, though such tools could unlock extensive benefits to human health. Here, we provide an overview of the current state of technological tools that may be used for microbiome engineering. These tools can enable investigators to define the parameters of a healthy microbiome and to determine how gut bacteria may contribute to the etiology of a variety of diseases. These tools may also allow us to explore the exciting prospect of developing targeted therapies and personalized treatments for microbiome-linked diseases.

Development of Cell-Based Sentinels for Nitric Oxide: Ensuring Marker Expression and Unimodality

We generated "sentinel" bacteria that respond to the biomarker nitric oxide (NO) and produce a homogeneous and strong fluorescent response. Our dual-plasmid system consists of a signal "relay" vector that employs an NO-responsive promoter that amplifies the native signal (via expression of T7 Polymerase (T7Pol)) to a second vector responsible for GFP expression. Importantly, to achieve an optimal "sentinel" response, we developed strategies that balance the transcriptional load within cells by altering (i) translation and (ii) activity of the T7Pol. Our optimized genetic circuitry was then used to transform commensal E. coli Nissle, as a proof-of-concept toward an ingestible cell-based sensor for Crohn's disease (CD) that, in turn, is marked by elevated levels of intestinal NO. Thus, the "biosensors" demonstrated here may serve as a simple diagnostic tool, contrasting the standard of care including colonoscopies or biopsies.

Engineering Diagnostic and Therapeutic Gut Bacteria

Genetically engineered bacteria have the potential to diagnose and treat a wide range of diseases linked to the gastrointestinal tract, or gut. Such engineered microbes will be less expensive and invasive than current diagnostics and more effective and safe than current therapeutics. Recent advances in synthetic biology have dramatically improved the reliability with which bacteria can be engineered with the sensors, genetic circuits, and output (actuator) genes necessary for diagnostic and therapeutic functions. However, to deploy such bacteria in vivo, researchers must identify appropriate gut-adapted strains and consider performance metrics such as sensor detection thresholds, circuit computation speed, growth rate effects, and the evolutionary stability of engineered genetic systems. Other recent reviews have focused on engineering bacteria to target cancer or genetically modifying the endogenous gut microbiota in situ. Here, we develop a standard approach for engineering "smart probiotics," which both diagnose and treat disease, as well as "diagnostic gut bacteria" and "drug factory probiotics," which perform only the former and latter function, respectively. We focus on the use of cutting-edge synthetic biology tools, gut-specific design considerations, and current and future engineering challenges.

Serotonin disturbs colon epithelial tolerance of commensal E. coli by increasing NOX2-derived superoxide

Adherent-invasive E. coli colonization and Toll-like receptor (TLR) expression are increased in the gut of inflammatory bowel disease (IBD) patients. However, the underlying mechanism of such changes has not been determined. In the current study, it was examined whether gut serotonin (5-hydroxytryptamine, 5-HT) can induce adherent-invasive E. coli colonization and increase TLR expression. In a co-culture system, commensal E. coli strain (BW25113, BW) adhered minimally to colon epithelial cells, but this was significantly enhanced by 5-HT to the level of a pathogenic strain (EDL933). Without inducing bacterial virulence, such as, biofilm formation, 5-HT enhanced BW-induced signaling in colon epithelial cells, that is, NADPH oxidase (NOX)-dependent superoxide production, the up-regulations of IL-8, TLR2, TLR4, and ICAM-1, and the down-regulations of E-cadherin and claudin-2. In a manner commensurate with these gene modulations, BW induced an increase in NF-κB and a decrease in GATA reporter signals in colon epithelial cells. However, 5-HT-enhanced BW adhesion and colon epithelial responses were blocked by knock-down of NOX2, TLR2, or TLR4. In normal mice, 5-HT induced the invasion of BW into gut submucosa, and the observed molecular changes were similar to those observed in vitro, except for significant increases in TNFα and IL-1β, and resulted in death. In dextran sulfate sodium-induced colitis mice (an IBD disease model), in which colonic 5-HT levels were markedly elevated, BW administration induced death in along with large amount of BW invasion into colon submucosa, and time to death was negatively related to the amount of BW injected. Taken together, our results demonstrate that 5-HT induces the invasion of commensal E. coli into gut submucosa by amplifying commensal bacteria-induced epithelial signaling (superoxide production and the inductions of NOX2 and TLR2/TLR4). The authors suggest that these changes may constitute the molecular basis for the pathogenesis of IBD.

Quantification of FITC-labelled probiotic Lactobacillus salivarius DSPV 001P during gastrointestinal transit in broilers

The knowledge related to the fate of probiotics in the complex environment of the intestinal microbiota in broilers is just beginning to be elucidated; however, it is not yet well understood. A good method to investigate the mechanisms by which probiotics mediate their effects is to mark probiotic bacteria and trace them. The aim of this research was to develop a new method to estimate in vivo fluorescein isothiocyanate (FITC)-labelled Lactobacillus salivarius DSPV 001P counts during passage through the gastrointestinal tract (GIT) of broilers. Forty-five, 1 d old Cobb broilers were used in this trial. Programmed necropsies were performed 30 min, 6 h, and 12 h after the administration of the probiotic bacterium, and samples of liver, crop, duodenum, caecum, and bursa of fabricius were collected. To determine the spatial and temporal transit of L. salivarius DSPV 001P in broilers, the number of bacteria as well as its respective fluorescent signal produced by FITC were measured. In order to observe the relationship between the variables, a logistic regression analysis was applied. The amount of fluorescence could be used as an indicator of fluorescent probiotic bacteria in the crop and duodenum 30 min after probiotic bacterium supplementation. In addition, the fluorescent signal could be used to estimate bacterial counts in caecum 6 and 12 h after L. salivarius DSPV 001P administration. To the best of our knowledge, this research is the first in vivo trial to employ the bacterial FITC-labelling technique in order to enumerate probiotic bacteria during gastrointestinal transit in broilers.

The pUltra plasmid series: A robust and flexible tool for fluorescent labeling of Enterobacteria

Fluorescent labeling has been an invaluable tool for the study of living organisms and bacterial species are no exception to this. Here we present and characterize the pUltra plasmids which express constitutively a fluorescent protein gene (GFP, RFP, YFP or CFP) from a strong synthetic promoter and are suitable for the fluorescent labeling of a broad range of Enterobacteria. The amount of expressed fluorophore from these genetic constructs is such, that the contours of the cells can be delineated on the basis of the fluorescent signal only. In addition, labeling through the pUltra plasmids can be used successfully for fluorescence and confocal microscopy while unambiguous distinction of cells labeled with different colors can be carried out efficiently by microscopy or flow cytometry. We compare the labeling provided by the pUltra plasmids with that of another plasmid series encoding fluorescent proteins and we show that the pUltra constructs are vastly superior in signal intensity and discrimination power without having any detectable growth rate effects for the bacterial population. We also use the pUltra plasmids to produce mixtures of differentially labeled pathogenic Escherichia, Shigella and Salmonella species which we test during infection of mammalian cells. We find that even inside the host cell, different strains can be distinguished effortlessly based on their fluorescence. We, therefore, conclude that the pUltra plasmids are a powerful labeling tool especially useful for complex biological experiments such as the visualization of ecosystems of different bacterial species or of enteric pathogens in contact with their hosts.

Genetically engineering of Escherichia coli and immobilization on electrospun fibers for drug delivery purposes

Engineered EcN bacteria were entrapped in core-sheath fibersviacoaxial electrospinning or grafted on the fiber surfaceviacovalent binding or affinity adsorption.

Potential probiotic Escherichia coli 16 harboring the Vitreoscilla hemoglobin gene improves gastrointestinal tract colonization and ameliorates carbon tetrachloride induced hepatotoxicity in rats

The present study describes the beneficial effects of potential probiotic E. coli 16 (pUC8:16gfp) expressing Vitreoscilla hemoglobin (vgb) gene, associated with bacterial respiration under microaerobic condition, on gastrointestinal (GI) colonization and its antioxidant activity on carbon tetrachloride (CCl₄) induced toxicity in Charles Foster rats. In vitro, catalase activity in E. coli 16 (pUC8:16gfp) was 1.8 times higher compared to E. coli 16 (pUC-gfp) control. In vivo, E. coli 16 (pUC8:16gfp) not only was recovered in the fecal matter after 70 days of oral administration but also retained antibacterial activities, whereas E. coli 16 (pUC-gfp) was not detected. Oral administration of 200 and 500 μL/kg body weight of CCl₄ to rats at weekly interval resulted in elevated serum glutamyl pyruvate transaminase (SGPT) and serum glutamyl oxalacetate transaminase (SGOT) levels compared to controls. Rats prefed with E. coli 16 (pUC8:16gfp) demonstrated near to normal levels for SGPT and SGOT, whereas the liver homogenate catalase activity was significantly increased compared to CCl₄ treated rats. Thus, pUC8:16gfp plasmid encoding vgb improved the growth and GI tract colonization of E. coli 16. In addition, it also enhanced catalase activity in rats harboring E. coli 16 (pUC8:16gfp), thereby preventing the absorption of CCl₄ to GI tract.

The long term oral regulation of blood glucose in diabetic patients by using of Escherichia coli Nissle 1917 expressing CTB-IGF-1 hybrid protein

Regarding to the high prevalence and comorbidities of chronic high blood glucose in diabetic patients and the limited efficacy and current painful treatments. It is necessary to improve new treatments that are non-invasive and long-term for controlling blood glucose. Recent studies have shown that the healthy microflora in different body organs can perform as the gene vectors for expressing different types of gene therapies in situ. We have proposed that by constructing a recombinant Escherichia coli Nissle 1917 that expresses CTB-IGF-1 hybrid gene under control of ompC glucose sensitive promoter, the intestinal glucose level can be regulated. This method in comparison with other methods is a non-invasive way to control the blood glucose orally and it can be used for all types of diabetes.

Intestinal bacterial translocation in rats with cirrhosis is related to compromised Paneth cell antimicrobial host defense

Liver cirrhosis is associated with bacterial translocation (BT) and endotoxemia. Most translocating bacteria belong to the common intestinal microbiota, suggesting a breakdown of intestinal barrier function. We hypothesized that diminished mucosal antimicrobial host defense could predispose to BT. Two rodent models of portal hypertension with increased BT were used, CCl(4)-induced ascitic cirrhosis and 2-day portal vein-ligated (PVL) animals. BT was assessed by standard microbiological techniques on mesenteric lymph nodes. Total RNA was isolated systematically throughout the intestinal tract, and expression of Paneth cell α-cryptdins and β-defensins was determined by real-time quantitative polymerase chain reaction (qPCR). To determine functional consequences, mucosal antimicrobial activity was assessed with a fluorescence-activated cell sorting assay. BT was detectable in 40% of rats with cirrhosis. Compared with the group without BT, these animals exhibited diminished intestinal Paneth cell α-cryptdin 5 and 7 expression. In contrast, PVL was associated with BT in all animals but did not affect antimicrobial peptides. The decrease in Paneth cell antimicrobials was most pronounced in the ileum and the coecum. Other antimicrobials showed no changes or even an induction in the case of BT at different sites. Antimicrobial activity toward different commensal strains was reduced, especially in the distal ileum and the cecum in experimental cirrhosis with BT (excluding PVL).

CONCLUSION

Compromised Paneth cell antimicrobial host defense seems to predispose to BT in experimental cirrhosis. Understanding this liver-gut axis including the underlying mechanisms could help us to find new treatment avenues.

Bacteriocinogeny in experimental pigs treated with indomethacin and Escherichia coli Nissle

AIM: To evaluate bacteriocinogeny in short-term high-dose indomethacin administration with or without probiotic Escherichia coli Nissle 1917 (EcN) in experimental pigs.

METHODS: Twenty-four pigs entered the study: Group A (controls), Group B (probiotics alone), Group C (indomethacin alone) and Group D (probiotics and indomethacin). EcN (3.5 × 10¹⁰ bacteria/d for 14 d) and/or indomethacin (15 mg/kg per day for 10 d) were administrated orally. Anal smears before and smears from the small and large intestine were taken from all animals. Bacteriocin production was determined with 6 different indicator strains; all strains were polymerase chain reaction tested for the presence of 29 individual bacteriocin-encoding determinants.

RESULTS: The general microbiota profile was rather uniform in all animals but there was a broad diversity in coliform bacteria (parallel genotypes A, B1, B2 and D found). In total, 637 bacterial strains were tested, mostly Escherichia coli (E. coli). There was a higher incidence of non-E. coli strains among samples taken from the jejunum and ileum compared to that of the colon and rectum indicating predominance of E. coli strains in the large intestine. Bacteriocinogeny was found in 24/77 (31%) before and in 155/560 (28%) isolated bacteria at the end of the study. Altogether, 13 individual bacteriocin types (out of 29 tested) were identified among investigated strains. Incidence of four E. coli genotypes was equally distributed in all groups of E. coli strains, with majority of genotype A (ranging from 81% to 88%). The following types of bacteriocins were most commonly revealed: colicins Ia/Ib (44%), microcin V (18%), colicin E1 (16%) and microcin H47 (6%). There was a difference in bacteriocinogeny between control group A (52/149, 35%) and groups with treatment at the end of the study: B: 31/122 (25%, P = 0.120); C: 43/155 (28%, P = 0.222); D: 29/134 (22%, P = 0.020). There was a significantly lower prevalence of colicin Ib, microcins H47 and V (probiotics group, P < 0.001), colicin E1 and microcin H47 (indomethacin group, P < 0.001) and microcins H47 and V (probiotics and indomethacin group, P = 0.025) compared to controls. Escherichia fergusonii (E. fergusonii) was identified in 6 animals (6/11 isolates from the rectum). One strain was non-colicinogenic, while all other strains of E. fergusonii solely produced colicin E1. All animals started and remained methanogenic despite the fact that EcN is a substantial hydrogen producer. There was an increase in breath methane (after the treatment) in 5/6 pigs from the indomethacin group (C).

CONCLUSION: EcN did not exert long-term liveability in the porcine intestine. All experimental pigs remained methanogenic. Indomethacin and EcN administered together might produce the worst impact on bacteriocinogeny.

Guide to designing, conducting, publishing and communicating results of clinical studies involving probiotic applications in human participants

The heterogeneity of human clinical trials to assess the effectiveness of probiotics presents challenges regarding interpretation and comparison. Evidence obtained from clinical trials among a population with a disease or specific risk factors may not be generalizable to healthy individuals. The evaluation of interventions in healthy persons requires careful selection of outcomes due to the absence of health indicators and the low incidence of preventable conditions. Given the tremendous resources invested in such trials, development of consistent approaches to assessing the effectiveness of probiotics would be beneficial. Furthermore, the reporting, presentation and communication of results may also affect the validity of the scientific evidence obtained from a trial. This review outlines the challenges associated with the design, implementation, data analysis and interpretation of clinical trials in humans involving probiotics. Best practices related to their design are offered along with recommendations for enhanced collaboration to advance research in this emerging field.

Oral Bifidobacterium modulates intestinal immune inflammation in mice with food allergy

BACKGROUND AND AIMS

It is proposed that probiotics have a therapeutic effect on the treatment of immune disorders. However, the underlying mechanisms require clarification. The present study aimed to evaluate the effect of gavage-feeding Bifidobacteria on suppression of T helper 2 (Th2) pattern inflammation in the intestines of mice with food allergy.

METHODS

Mice were sensitized to ovalbumin to induce the intestinal Th2 pattern inflammation. Allergic mice were treated with or without Bifidobacteria via gavage-feeding. Th2 response, number of regulatory T cells (Treg) in the spleen and intestine, intestinal epithelial barrier function and bifidobacterial translocation were examined.

RESULTS

The results showed that serum-specific immunoglobulin E antibody and interleukin 4 (IL-4) were increased in allergic mice. Intestinal epithelial barrier function was impaired in allergic mice as shown by the increase in epithelial ion secretion and permeability to macromolecular protein horseradish peroxidase in Ussing chambers. Number of Treg was decreased in both spleen and intestines of allergic mice. Gavage-feeding Bifidobacteria significantly suppressed the skewed Th2 response and increased the number of Treg. Transient bifidobacterial translocation was observed in allergic mice.

CONCLUSIONS

Oral administration of Bifidobacteria has the capacity to suppress the skewed Th2 response in allergic mice, increasing the number of Treg and IL-10-positive cells and improve the impaired intestinal epithelial barrier function.

Gut microbiota and probiotics in modulation of epithelium and gut-associated lymphoid tissue function

The intestinal tract mucosa is exposed to a vast number of environmental antigens and a large community of commensal bacteria. The mucosal immune system has to provide both protection against pathogens and tolerance to harmless bacteria. Immune homeostasis depends on the interaction of indigenous commensal and transient bacteria (probiotics) with various components of the epithelium and the gut-associated lymphoid tissue. Herein, an update is given of the mechanisms by which the gut microbiota and probiotics are translocated through the epithelium, sensed via pattern-recognition receptors, and activate innate and adaptive immune responses.

Oral probiotic control skin inflammation by acting on both effector and regulatory T cells

Probiotics are believed to alleviate allergic and inflammatory skin disorders, but their impact on pathogenic effector T cells remains poorly documented. Here we show that oral treatment with the probiotic bacteria L. casei (DN-114 001) alone alleviates antigen-specific skin inflammation mediated by either protein-specific CD4⁺ T cells or hapten-specific CD8⁺ T cells. In the model of CD8⁺ T cell-mediated skin inflammation, which reproduces allergic contact dermatitis in human, inhibition of skin inflammation by L. casei is not due to impaired priming of hapten-specific IFNγ-producing cytolytic CD8⁺ effector T cells. Alternatively, L. casei treatment reduces the recruitment of CD8⁺ effector T cells into the skin during the elicitation (i.e. symptomatic) phase of CHS. Inhibition of skin inflammation by L. casei requires MHC class II-restricted CD4⁺ T cells but not CD1d-restricted NK-T cells. L casei treatment enhanced the frequency of FoxP3⁺ Treg in the skin and increased the production of IL-10 by CD4⁺CD25⁺ regulatory T cells in skin draining lymph nodes of hapten-sensitized mice. These data demonstrate that orally administered L. casei (DN-114 001) efficiently alleviate T cell-mediated skin inflammation without causing immune suppression, via mechanisms that include control of CD8⁺ effector T cells and involve regulatory CD4⁺ T cells. L. casei (DN-114 001) may thus represent a probiotic of potential interest for immunomodulation of T cell-mediated allergic skin diseases in human.

Application of sequence-dependent electrophoresis fingerprinting in exploring biodiversity and population dynamics of human intestinal microbiota: what can be revealed?

Sequence-dependent electrophoresis (SDE) fingerprinting techniques such as denaturing gradient gel electrophoresis (DGGE) have become commonplace in the field of molecular microbial ecology. The success of the SDE technology lays in the fact that it allows visualization of the predominant members of complex microbial ecosystems independent of their culturability and without prior knowledge on the complexity and diversity of the ecosystem. Mainly using the prokaryotic 16S rRNA gene as PCR amplification target, SDE-based community fingerprinting turned into one of the leading molecular tools to unravel the diversity and population dynamics of human intestinal microbiota. The first part of this review covers the methodological concept of SDE fingerprinting and the technical hurdles for analyzing intestinal samples. Subsequently, the current state-of-the-art of DGGE and related techniques to analyze human intestinal microbiota from healthy individuals and from patients with intestinal disorders is surveyed. In addition, the applicability of SDE analysis to monitor intestinal population changes upon nutritional or therapeutic interventions is critically evaluated.

Clinical use of E. coli Nissle 1917 in inflammatory bowel disease

The probiotic Escherichia coli strain Nissle 1917 is in addition to some Lactobacilli sp. one of the best-studied probiotic strains. This particular E. coli strain was isolated in 1917 based on its potential to protect from presumably infectious gastroenteritis. Initial therapeutic success was noted in the management of gastrointestinal infectious disorders and infections affecting the urinary tract; the focus shifted later to chronic inflammatory conditions. The unique combination of fitness and survival factors to support intestinal survival, the lack of virulence, and obvious probiotic properties make this microorganism a safe and effective candidate in the treatment of chronic inflammatory bowel diseases. Three large clinical trials have assessed the potential in the maintenance of remission of ulcerative colitis and equivalence to standard 5-ASA medication was documented. This review aims to discuss important mechanisms of E. coli Nissle 1917 and will review the available literature regarding treatment of inflammatory bowel diseases.

Rationale for probiotic treatment strategies in inflammatory bowel disease

Chronic inflammatory bowel diseases (IBD), such as Crohn's disease and ulcerative colitis, are recurrent and aggressive inflammatory disorders that are most likely the result of an overly aggressive immune response to ubiquitous intestinal antigens in a genetically susceptible host. Despite decades of intense research, our knowledge of factors causing IBD remains incomplete and, therefore, conventional therapy to induce and maintain remission works in a symptomatic fashion, merely suppressing the immune response. Probiotic bacteria have long been known to confer health benefits, especially with regard to intestinal disorders. Although there is mounting evidence from in vitro and animal experiments supporting the use of probiotics in IBD, clinical trials have not provided definite evidence for the therapeutic effect of probiotic therapy in IBD to date. This is with the notable exception of pouchitis and the maintenance of remission in ulcerative colitis, whereas Crohn's disease and active ulcerative colitis do not seem amenable to probiotic intervention. The next 5 years will see more trials targeting specific clinical settings using tailor-made probiotic combinations, taking into account our increasing knowledge of individual probiotic properties and the diversity of these microorganisms.

Use of green fluorescent protein to monitorLactobacillusin the gastro-intestinal tract of chicken

Lactobacilli, like other gut commensal bacteria, are well known for their use in industrial food fermentations and for their probiotic properties. However, little is known about the interaction of these microorganisms with the gastro-intestinal epithelia when administered in vivo. To specifically monitor the passage of lactobacilli after oral administration, the gfp gene was cloned downstream from the constitutive l-lactate dehydrogenase promoter (pldhL) in the experiment. The recombinant expression vector pLEM415::gfp was electroporated into different lactobacilli isolated from chicken. Green fluorescent protein (GFP) was expressed successfully in Lactobacillus delbrueckii ssp. lactis D17 (D17-GFP) and Lactobacillus fructosus C2 (C2-GFP). Moreover, oral administration of D17-GFP in chickens allowed us to trace it in the gastro-intestinal tract. Six hours after ingestion, D17-GFP was detectable in all luminal contents (stomach, jejunum, ileum and caecum). At 42 h post-administration the microorganism was present throughout the intestine with maximum concentrations about 10(5.5) in all intestinal sections. No fluorescent lactobacilli were detected in the spleen or liver of chickens at any time. Using fluorescence microscopy, it became apparent that the D17-GFP were mainly embedded in the mucus, localized close to the epithelial surface of the intestine and scattered in the intestine lamina propria.

Cross-talk between probiotic bacteria and the host immune system

Among the numerous purported health benefits attributed to probiotic bacteria, their capacity to interact with the immune system of the host is now supported by an increasing number of in vitro and in vivo experiments. In addition to these, a few well-controlled human intervention trials aimed at preventing chronic immune dysregulation have been reported. Even though the precise molecular mechanisms governing the cross-talk between these beneficial bacteria and the intestinal ecosystem remain to be discovered, a new and fascinating phase of research has been initiated in this area as demonstrated by a series of recent articles. This article summarizes the status and latest progress of the field in selected areas and aims at identifying key questions that remain to be addressed, especially concerning the translocation of ingested bacteria, the identification of major immunomodulatory compounds of probiotics, and specific aspects of the host-microbe cross-talk. The interaction with immunocompetent cells and the role of secretory IgA in gut homeostasis are also evoked. Finally, a brief overview is provided on the potential use of recombinant DNA technology to enhance the health benefits of probiotic strains and to unravel specific mechanisms of the host-microbe interaction.

Beneficial lactobacilli in food and feed: long-term use, biodiversity and proposals for specific and realistic safety assessments

Lactobacilli have played a crucial role in the production of fermented products for millennia. Their probiotic effects have recently been studied and used in new products. Isolated cases of lactobacillemia have been reported in at-risk populations, but lactobacilli present an essentially negligible biological risk. We analyzed the current European guidelines for safety assessment in food/feed and conclude that they are not relevant for the Lactobacillus genus. We propose new specific guidelines, beginning by granting a 'long-standing presumption of safety' status to Lactobacillus genus based on its long history of safe use. Then, based on the available body of knowledge and intended use, only such tests as are useful will be necessary before attributing 'qualified presumption of safety' status.

Biofilm formation by bacterial associations under various salinities and copper ion stress

The study addresses the effect of abiotic (medium salinity and copper ions) and biotic (interactions between populations) factors on the formation of structured communities by binary associations consisting of halotolerant bacteria (Alcaligenes sp. 1-1 or Acinetobacter sp. 1-19) and a wild-type B. subtilis 2335 strain or a transgenic strain. The results showed that 250 mg l(-1) of copper ions inhibit formation of biofilms by monocultures of the tested strains. Binary associations of the strains were more resistant to high concentrations (250 mg l(-1)) of copper ions. At the lowest NaCl concentration (0.05% and 2.5%) and in the presence of copper ions, bacilli seemed to help halotolerant bacteria survive. Under increased salinity and in the presence of copper ions, structured communities developed due to halotolerant bacteria. Coexistence under stressful conditions was beneficial for the both groups of bacteria.