Induction of human beta-defensin 2 by the probiotic Escherichia coli Nissle 1917 is mediated through flagellin

More than a marine propeller--the flagellum of the probiotic Escherichia coli strain Nissle 1917 is the major adhesin mediating binding to human mucus

The flagellum of the probiotic Escherichia coli strain Nissle 1917 (EcN) is not just responsible for motility, but also for EcN's ability to induce the production of human β-defensin 2. Here, we report a third function of this EcN organell. In this study we investigated the role of the EcN flagellum in adhesion to different host tissues by ex vivo and in vitro studies. Ex vivo studies with cryosections of human gut biopsies revealed that the flagellum of EcN is most likely important for efficient adhesion to the human intestinal tract. These results and in vitro studies with different epithelial cells indicated that the presence of mucus is important for efficient mediation of adhesion by the flagellum of EcN. We observed direct interaction between isolated flagella from EcN wild type and porcine mucin 2 as well as human mucus. However, we could not observe any interaction of the flagella with murine mucus. For the first time, we identified the mucus component gluconate as one receptor for the binding of flagella from EcN and were able to exclude the flagellin domain D3 as a responsible interaction partner. We propose that the flagellum of EcN is its major adhesin in vivo, which enables this probiotic strain to compete efficiently for binding sites on host tissue with several bacterial pathogens.

Pseudomonas aeruginosa-derived rhamnolipids subvert the host innate immune response through manipulation of the human beta-defensin-2 expression

Pseudomonas aeruginosa is a well-known cause of infections especially in compromised patients. To neutralize this pathogen, the expression of antimicrobial factors in epithelial cells is crucial. In particular the human beta-defensin hBD-2 is especially active against P. aeruginosa. In this study, we identified rhamnolipids in P. aeruginosa culture supernatants that are able to prevent the pathogen-induced hBD-2 response in keratinocytes. The presence of rhamnolipids within the host cells and inhibition assays suggest that calcium-regulated pathways and protein kinase C activation are impaired by rhamnolipids. In consequence, the induction of hBD-2 in keratinocytes by P. aeruginosa-derived flagellin as well as the host's own hBD-2 mediator interleukin IL-1β is inhibited. Strikingly, rhamnolipids did not affect the release of the proinflammatory mediator interleukin IL-8 by flagellin. Thus, in addition to their function in establishment and persistence of P. aeruginosa infections, rhamnolipids can be engaged by P. aeruginosa for a targeted attenuation of the innate immunity to manage its survival and colonization on compromised epithelia.

Innate immune dysfunction in inflammatory bowel disease

The pathogenetic mechanisms that cause the two types of inflammatory bowel disease (IBD), Crohn's disease (CD) and ulcerative colitis (UC), are still under investigation. Nevertheless, there is broad agreement that luminal microbes are of particular relevance in the development of these conditions. In recent years, increasing evidence has shown that defects in the innate immunity are at the centre of both types of IBD. The innate intestinal barrier is provided by the epithelium which secretes antimicrobial peptides (so-called defensins) that are retained in the mucus layer. In ileal CD, the alpha-defensins are lacking owing to several Paneth cell defects. In colonic CD, the expression of beta-defensins is inadequate. This may be related to downregulation of the transcription factor peroxisome proliferator-activated receptor-gamma and in some cohorts is associated with a reduced HBD2 gene copy number. In UC, the mucus layer, which protects the host from the enormous amounts of luminal microbes, is defective. This is accompanied by an insufficient differentiation from intestinal stem cells towards goblet cells. All these disturbances in the gut barrier shift the balance from epithelial defence towards bacterial offence. The current treatment for CD and UC is based on suppression of this secondary inflammatory process. In future, patients may benefit from new therapeutic approaches stimulating the protective innate immune system.

Innate immune signaling in defense against intestinal microbes

The gastrointestinal system is a common entry point for pathogenic microbes to access the inner environment of the body. Anti-microbial factors produced by the intestinal mucosa limit the translocation of both commensal and pathogenic microbes across the intestinal epithelial cell barrier. The regulation of these host defense mechanisms largely depends on the activation of innate immune receptors by microbial molecules. Under steady-state conditions, the microbiota provides constitutive signals to the innate immune system, which helps to maintain a healthy inflammatory tone within the intestinal mucosa and, thus, enhances resistance to infection with enteric pathogens. During an acute infection, the intestinal epithelial cell barrier is breached, and the detection of microbial molecules in the intestinal lamina propria rapidly stimulates innate immune signaling pathways that coordinate early defense mechanisms. Herein, we review how microbial molecules shed by both commensal and pathogenic microbes direct host defenses at the intestinal mucosa. We highlight the signaling pathways, effector molecules, and cell populations that are activated by microbial molecule recognition and, thereby, are involved in the maintenance of homeostatic levels of host defense and in the early response to acute enteric infection. Finally, we discuss how manipulation of these host defense pathways by stimulating innate immune receptors is a potential therapeutic strategy to prevent or alleviate intestinal disease.

Avirulent K88 (F4)+ Escherichia coli strains constructed to express modified enterotoxins protect young piglets from challenge with a virulent enterotoxigenic Escherichia coli strain that expresses the same adhesion and enterotoxins

Virulence of enterotoxigenic Escherichia coli (ETEC) is associated with fimbrial adhesins and enterotoxins such as heat-labile (LT) and/or heat-stable (ST) enterotoxins. Previous studies using a cell culture model suggest that exclusion of ETEC from attachment to epithelial cells requires expression of both an adhesin such as K88 (F4) fimbriae, and LT. To test the ability of non-pathogenic E. coli constructs to exclude virulent ETEC sufficiently to prevent clinical disease, we utilized a piglet ETEC challenge model. Thirty-nine 5-day-old piglets were inoculated with a placebo (control), or with either of the three K88(+)E. coli strains isogenic with regard to modified LT expression: 8017 (pBR322 plasmid vector control), non-toxigenic mutant 8221 (LT(R192G)) in pBR322, or 8488, with the LT gene fused to the STb gene in pBR322 (LT(R192G)-STb). Piglets were challenged with virulent ETEC Strain 3030-2 (K88(+)/LT/STb) 24h post-inoculation. K88ac receptor-positive piglets in the control group developed diarrhea and became dehydrated 12-24h post-challenge. Piglets inoculated with 8221 or 8488 did not exhibit clinical signs of ETEC disease; most piglets inoculated with 8017 showed diarrhea. Control pigs exhibited significant weight loss, increased blood total protein, and higher numbers of colony-forming units of 3030-2 E. coli in washed ileum and jejunum than treated pigs. This study shows for the first time that pre-inoculation with an avirulent strain expressing adhesive fimbriae and a non-toxic form of LT provides significant short term protection from challenge with a virulent ETEC strain that expresses the same fimbrial adhesion and enterotoxin.

Modulating immunity as a therapy for bacterial infections

Despite our efforts to halt the increase and spread of antimicrobial resistance, bacteria continue to become less susceptible to antimicrobial drugs over time, and rates of discovery for new antibiotics are declining. Thus, it is essential to explore new paradigms for anti-infective therapy. One promising approach involves host-directed immunomodulatory therapies, whereby natural mechanisms in the host are exploited to enhance therapeutic benefit. The objective is to initiate or enhance protective antimicrobial immunity while limiting inflammation-induced tissue injury. A range of potential immune modulators have been proposed, including innate defence regulator peptides and agonists of innate immune components such as Toll-like receptors and NOD-like receptors.

Modern approaches in probiotics research to control foodborne pathogens

Foodborne illness is a serious public health concern. There are over 200 known microbial, chemical, and physical agents that are known to cause foodborne illness. Efforts are made for improved detection, control and prevention of foodborne pathogen in food, and pathogen associated diseases in the host. Several commonly used approaches to control foodborne pathogens include antibiotics, natural antimicrobials, bacteriophages, bacteriocins, ionizing radiations, and heat. In addition, probiotics offer a potential intervention strategy for the prevention and control of foodborne infections. This review focuses on the use of probiotics and bioengineered probiotics to control foodborne pathogens, their antimicrobial actions, and their delivery strategies. Although probiotics have been demonstrated to be effective in antagonizing foodborne pathogens, challenges exist in the characterization and elucidation of underlying molecular mechanisms of action and in the development of potential delivery strategies that could maintain the viability and functionality of the probiotic in the target organ.

Dextran sodium sulfate-induced inflammation alters the expression of proteins by intestinal Escherichia coli strains in a gnotobiotic mouse model

To identify Escherichia coli proteins involved in adaptation to intestinal inflammation, mice were monoassociated with the colitogenic E. coli strain UNC or with the probiotic E. coli strain Nissle. Intestinal inflammation was induced by treating the mice with 3.5% dextran sodium sulfate (DSS). Differentially expressed proteins in E. coli strains collected from cecal contents were identified by 2-dimensional difference gel electrophoresis. In both strains, acute inflammation led to the downregulation of pathways involved in carbohydrate breakdown and energy generation. Accordingly, DSS-treated mice had lower concentrations of bacterial fermentation products in their cecal contents than control mice. Differentially expressed proteins also included the Fe-S cluster repair protein NfuA, the tryptophanase TnaA, and the uncharacterized protein YggE. NfuA expression was 3-fold higher in E. coli strains from DSS-treated than from control mice. Reporter experiments confirmed the induction of nfuA in response to iron deprivation, mimicking Fe-S cluster destruction by inflammation. YggE expression, which has been reported to reduce the intracellular level of reactive oxygen species, was 4- to 8-fold higher in E. coli Nissle than in E. coli UNC. This was confirmed by in vitro reporter gene assays indicating that Nissle is better equipped to cope with oxidative stress than UNC. Nissle isolated from DSS-treated and control mice had TnaA levels 4- to 7-fold-higher than those of UNC. Levels of indole resulting from the TnaA reaction were higher in control animals associated with E. coli Nissle. Because of its anti-inflammatory effect, indole is hypothesized to be involved in the extension of the remission phase in ulcerative colitis described for E. coli Nissle.

Effect of yoghurt containing Bifidobacterium lactis Bb12® on faecal excretion of secretory immunoglobulin A and human beta-defensin 2 in healthy adult volunteers

BACKGROUND

Probiotics are used to provide health benefits. The present study tested the effect of a probiotic yoghurt on faecal output of beta-defensin and immunoglobulin A in a group of young healthy women eating a defined diet.

FINDINGS

26 women aged 18-21 (median 19) years residing in a hostel were given 200 ml normal yoghurt every day for a week, followed by probiotic yoghurt containing Bifidobacterium lactis Bb12® (10⁹ in 200 ml) for three weeks, followed again by normal yoghurt for four weeks. Stool samples were collected at 0, 4 and 8 weeks and assayed for immunoglobulin A and human beta-defensin-2 by ELISA. All participants tolerated both normal and probiotic yoghurt well. Human beta-defensin-2 levels in faeces were not altered during the course of the study. On the other hand, compared to the basal sample, faecal IgA increased during probiotic feeding (P = 0.0184) and returned to normal after cessation of probiotic yoghurt intake.

CONCLUSIONS

Bifidobacterium lactis Bb12® increased secretory IgA output in faeces. This property may explain the ability of probiotics to prevent gastrointestinal and lower respiratory tract infections.

Probiotics in the management of gastrointestinal disease: analysis of the attitudes and prescribing practices of gastroenterologists and surgeons

OBJECTIVE

Probiotics are increasingly advocated in the management of various gastrointestinal disorders. The aim of this study was to investigate the current attitudes and prescribing practices of surgeons and gastroenterologists for probiotics in the treatment of gastrointestinal disorders.

METHODS

A questionnaire was designed to look at the frequency of probiotic prescribing, types of probiotics used, indications for and duration of treatment and clinicians' experiences with probiotic use. A total of 220 questionnaires were mailed to consultant gastroenterologists and surgeons practicing in the UK.

RESULTS

The overall response rate was 80.5%, of which 69.5% of respondents said they recommended or prescribed probiotic food supplements to their patients, including 53.4% of surgeons and 80.8% of gastroenterologists (P = 0.00013). The most popular probiotic supplements among surgeons were probiotic-containing yoghurt and drinks (79.5% and 71.8%, respectively), whereas VSL#3 was more popular with gastroenterologists (83.3%). The most popular indications were irritable bowel syndrome (70.7% of prescribers) and pouchitis (67.5% of prescribers). Many respondents prescribed long-term probiotics. Most consultants had been prescribing probiotics for a period of 1 to 5 years.

CONCLUSION

Probiotics are popular among gastroenterologists and surgeons in the UK for the treatment of gastrointestinal disorders. Further evidence to support their routine use, by way of large, well-designed randomized controlled trials, is necessary.

Emerging molecular insights into the interaction between probiotics and the host intestinal mucosa

Probiotic bacteria can modulate immune responses in the host gastrointestinal tract to promote health. The genomics era has provided novel opportunities for the discovery and characterization of bacterial probiotic effector molecules that elicit specific responses in the intestinal system. Furthermore, nutrigenomic analyses of the response to probiotics have unravelled the signalling and immune response pathways which are modulated by probiotic bacteria. Together, these genomic approaches and nutrigenomic analyses have identified several bacterial factors that are involved in modulation of the immune system and the mucosal barrier, and have revealed that a molecular 'bandwidth of human health' could represent a key determinant in an individual's physiological responsiveness to probiotics. These approaches may lead to improved stratification of consumers and to subpopulation-level probiotic supplementation to maintain or improve health, or to reduce the risk of disease.

Structural bacterial molecules as potential candidates for an evolution of the classical concept of probiotics

A large number of experimental and clinical studies published in recent years have demonstrated the beneficial role of probiotic bacteria in the health of the host. However, because the different receptors of the innate immune system can recognize only specific bacterial molecular patterns, knowledge of the role played by individual probiotic molecular patterns is essential to move from the current confused era of live probiotic bacteria to the era of the pharmacobiotic strategies. This article reviews the current knowledge on the probiotic activities of bacterial structural molecules (nucleic acids and surface molecules), which represent the fundamental basis to set up experimental and clinical studies in this emerging field with very promising and potentially invaluable future prospects.

Probiotics, nuclear receptor signaling, and anti-inflammatory pathways

There is increased investigation of the human microbiome as it relates to health and disease. Dysbiosis is implicated in various clinical conditions including inflammatory bowel disease (IBD). Probiotics have been explored as a potential treatment for IBD and other diseases. The mechanism of action for probiotics has yet to be fully elucidated. This paper discusses novel mechanisms of action for probiotics involving anti-inflammatory signaling pathways. We highlight recent progress in probiotics and nuclear receptor signaling, such as peroxisome-proliferator-activated receptor gamma (PPARγ) and vitamin D receptor (VDR). We also discuss future areas of investigation.

Probiotics and gastrointestinal diseases

The intestinal microbiota plays a key role in maintaining the normal function of the human gastrointestinal tract. Many probiotics are derived from human gut flora, and have been confirmed to be valuable in the management of gastrointestinal diseases. Probiotic effects are strain-specific, they do not act through the same mechanisms, and nor are all probiotics good for health. Nevertheless, they do have several common characters in that they exert anti-inflammatory effects, they employ different strategies to antagonize competing microorganisms, and they induce cytoprotective changes in the host either through enhancement of barrier function, or through up-regulation of the expression of cytoprotective host proteins. In this review we focus on several probiotics: a Gram-negative probiotic (Escherichia coli Nissle1917), a Gram-positive probiotic bacterium (Lactobacillus Rhamnosus GG, LGG), a bacterial mixture (VSL#3), and a yeast probiotic (Saccharomyces boulardii).

Innate antimicrobial immunity in inflammatory bowel diseases

Inflammatory bowel diseases are characterized by chronic intestinal inflammation at different sites. Data from animal models as well as human patients including gene-association studies suggest that different components of the innate barrier function are primarily defective. These recent advances support the evolving hypothesis that intestinal bacteria induce inflammation predominantly as a result of a weakened innate mucosal barrier in genetically predisposed individuals. This article discusses our current understanding of the primary events of disease. Together, these findings should result in new therapeutic avenues aimed at restoring antimicrobial barrier function to prevent a bacterial-triggered inflammatory response.

Altered host-microbe interaction in HIV: a target for intervention with pro- and prebiotics

The intestinal immune system is severely affected by HIV and circulating microbial products from the intestinal tract that provide an ongoing source of systemic inflammation and concomitant viral replication. In addition, HIV-infected individuals can have a deregulated immune response that may hamper the anti-viral capacity of the host. Various probiotic organisms and prebiotic agents have been shown to enhance intestinal epithelial barrier functions, reduce inflammation, and support effective Th-1 responses. As these characteristics may benefit HIV patients, this review aims to provide a theoretical framework for the development of probiotic and prebiotic interventions specifically for this population.

'Gut health': a new objective in medicine?

'Gut health' is a term increasingly used in the medical literature and by the food industry. It covers multiple positive aspects of the gastrointestinal (GI) tract, such as the effective digestion and absorption of food, the absence of GI illness, normal and stable intestinal microbiota, effective immune status and a state of well-being. From a scientific point of view, however, it is still extremely unclear exactly what gut health is, how it can be defined and how it can be measured. The GI barrier adjacent to the GI microbiota appears to be the key to understanding the complex mechanisms that maintain gut health. Any impairment of the GI barrier can increase the risk of developing infectious, inflammatory and functional GI diseases, as well as extraintestinal diseases such as immune-mediated and metabolic disorders. Less clear, however, is whether GI discomfort in general can also be related to GI barrier functions. In any case, methods of assessing, improving and maintaining gut health-related GI functions are of major interest in preventive medicine.

A flagellin-producing Lactococcus strain: interactions with mucin and enteropathogens

Bacillus cereus CH is a probiotic strain used in human nutrition whose adhesion to mucin is dependent on its surface-associated flagellin. Flagellins from the surface of several probiotic Bacillus strains were efficiently extracted with 5 M LiCl and identified by peptide fingerprinting. Based on the proteomic analysis, cloning of the gene coding for the flagellin of B. cereus CH was performed in the lactococcal vector pNZ8110 under the control of a nisin-inducible promoter. The resulting strain, Lactococcus lactis CH, produced a surface-associated flagellin after 6 h of induction with nisin. The recombinant Lactococcus strain adhered strongly to mucin-coated polystyrene plates, whilst inhibiting competitively the adhesion of the pathogens Escherichia coli LMG2092 and Salmonella enterica ssp. enterica LMG15860 to the same molecule. Strain CH could be used in further experimentation for the characterization of the molecular mechanism of action of this probiotic B. cereus CH flagellin.

Treatment with Lactobacillus acidophilus cell wall extract and DNA improves experimental acute colitis in mice

AIM: To investigate the effect of treatment with Lactobacillus acidophilus (L.acidophilus) cell wall extract (BCW) and DNA on experimental colitis in mice.

METHODS: Forty 6-8-wk-old specific pathogen-free female BALB/c mice were randomly divided into four groups: normal group, L.acidophilus BCW-treated group, L.acidophilus DNA-treated group, and control group. Except the normal group, other groups of mice were subjected to induction of experimental colitis with 1.5% DSS in drinking water for 7 d and then treated with L.acidophilus BCW (20 μg/10 g), L.acidophilus DNA (0.2 μg/10 g), and physiological saline (0.2 mL/10 g), respectively. The changes in body weight, fecal traits, and faecal occult bleeding were recorded each day. All animals were killed on day 8 to isolate the whole colon for examination of length and wet weight. Hematoxylin and eosin staining of colonic sections was performed. The effect of treatment with L.acidophilus BCW and DNA on experimental colitis was then evaluated.

RESULTS: Compared with the control group, weight loss was significantly improved (2.94 g ± 0.78 g, 3.37 g ± 1.08 g vs 6.96 g ± 1.39 g, both P < 0.05) and DAI score was significantly decreased (4.27 ± 0.41, 4.62 ± 0.56 vs 6.85 ± 0.94, both P < 0.05) in mice treated with both L.acidophilus BCW and DNA. Treatment with L.acidophilus BCW and DNA prevented the shortening of colon length (8.62 cm ± 1.31 cm, 8.15 cm ± 0.97 cm vs 6.63 cm ± 1.38 cm, both P < 0.05), increased the colon/body weight index (1.63% ± 0.27%, 1.68% ± 0.29% vs 2.12% ± 0.22%, both P < 0.05), improved mucosal damage and inflammatory infiltration, and protected mucosal glands and villi.

CONCLUSION: Treatment with L.acidophilus cell wall extract and DNA can improve DSS-induced experimental colitis in mice.

Defensin-immunology in inflammatory bowel disease

Defensins are endogenous antibiotics with microbicidal activity against Gram-negative and Gram-positive bacteria, fungi, enveloped viruses and protozoa. A disturbed antimicrobial defense, as provided by Paneth- and other epithelial cell defensins, seems to be a critical factor in the pathogenesis of inflammatory bowel diseases. Conspicuously, there is a relative lack of Paneth cell beta-defensins HD-5 and HD-6 in ileal Crohn's disease, both in the absence of a pattern recognition receptor NOD2 mutation and, even more pronounced, in its presence. This deficit is independent of concurrent active inflammation and results in a diminished antibacterial killing by the mucosa. The Crohn's disease mucosa has not only a significant lack in killing different Escherichia coli but also an impaired ability in clearing Staphylococcus aureus as well as anaerobic micro-organisms. Thus, this dysfunction in antibacterial barrier seems to be broad and is not restricted to a single bacterial strain. In addition to directly controlling barrier function, Paneth cell defensins also regulate the composition of the bacterial stool flora. In the majority of patients, the Paneth cell deficiency is mediated by WNT signalling which suggests a disturbed Paneth cell differentiation in ileal Crohn's disease. In contrast, colonic Crohn's disease is characterised by an impaired induction of mucosal beta-defensins, partly due to a low copy number of the beta-defensin gene cluster. Therefore it seems plausible that bacteria take advantage of a niche formed by defensin deficiency. This would represent a paradigm shift in understanding Crohn's disease and provides a target for future therapeutic strategies.

Interference of Bifidobacterium choerinum or Escherichia coli Nissle 1917 with Salmonella Typhimurium in gnotobiotic piglets correlates with cytokine patterns in blood and intestine

The colonization, translocation and protective effect of two intestinal bacteria - PR4 (pig commensal strain of Bifidobacterium choerinum) or EcN (probiotic Escherichia coli strain Nissle 1917) - against subsequent infection with a virulent LT2 strain of Salmonella enterica serovar Typhimurium were studied in gnotobiotic pigs after oral association. The clinical state of experimental animals correlated with bacterial translocation and levels of inflammatory cytokines [a chemokine, interleukin (IL)-8, a proinflammatory cytokine, tumour necrosis factor (TNF)-α and an anti-inflammatory cytokine, IL-10] in plasma and intestinal lavages. Gnotobiotic pigs orally mono-associated with either PR4 or EcN thrived, and bacteria were not found in their blood. No significant inflammatory cytokine response was observed. Mono-association with Salmonella caused devastating septicaemia characterized by high levels of IL-10 and TNF-α in plasma and TNF-α in the intestine. Di-associated gnotobiotic pigs were given PR4 or EcN for 24 h. Subsequently, they were infected orally with Salmonella and euthanized 24 h later. Pigs associated with bifidobacteria before Salmonella infection suffered from severe systemic infection and mounted similar cytokine responses as pigs infected with Salmonella alone. In contrast, EcN interfered with translocation of Salmonella into mesenteric lymph nodes and systemic circulation. Pigs pre-associated with EcN thrived and their clinical condition correlated with the absence of IL-10 in their plasma and a decrease of TNF-α in plasma and ileum.

Probiotic Escherichia coli Nissle 1917 activates DC and prevents house dust mite allergy through a TLR4-dependent pathway

Experimental animal and human studies have demonstrated that probiotic strains have beneficial effects on allergy. Here we report that the probiotic Escherichia coli Nissle 1917 strain (EcN) is able to activate DC, as shown by important cytokine synthesis together with up-regulation of membrane expression of CD40, CD80 and CD86. This EcN-induced DC activation was strictly dependent on the TLR4 signaling pathway and was also associated with stimulation of NF-kappaB and MAPK. We next investigated the prophylactic potential of i.n. co-administration of EcN with a recombinant form of Der p 1 (ProDer p 1) in a murine model of mite allergy. I.n. vaccinations with EcN plus ProDer p 1 prevented the subsequent allergic response following Der p 1 sensitization and airway challenge with aerosolized mite extracts through the induction of an allergen-specific IgG2a response, the prevention of specific IgE production and a strong reduction of IL-5 secretion by allergen-restimulated splenocytes. EcN alone or in combination with ProDer p 1 inhibited the development of airway eosinophilia and neutrophilia. This in vivo protective effect of EcN was, in part, mediated by TLR4 signaling. Our results suggest that EcN represents an efficient adjuvant to prevent allergic responses.

Paneth's disease

In about 70% of patients Crohn's disease (CD) affects the small intestine. This disease location is stable over time and associated with a genetic background different from isolated colonic disease. A characteristic feature of small intestinal host defense is the presence of Paneth cells at the bottom of the crypts of Lieberkühn. These cells produce different broad spectrum antimicrobial peptides (AMPs) most abundantly the α-defensins HD-5 and -6 (DEFA5 und DEFA6). In small intestinal Crohn's disease both these PC products are specifically reduced. As a functional consequence, ileal extracts from Crohn's disease patients are compromised in clearing bacteria and enteroadherent E. coli colonize the mucosa. Mechanisms for defective antimicrobial Paneth cell function are complex and include an association with a NOD2 loss of function mutation, a disturbance of the Wnt pathway transcription factor TCF7L2 (also known as TCF4), the autophagy factor ATG16L1, the endosomal stress protein XBP1, the toll-like receptor TLR9, the calcium mediated potassium channel KCNN4 as well as mutations or inactivation of HD5. Thus we conclude that small intestinal Crohn's disease is most likely a complex disease of the Paneth cell: Paneth's disease.

Modulation of natural immunity in the gut by Escherichia coli strain Nissle 1917

The beneficial effect of probiotic Escherichia coli strain Nissle 1917 (EcN) suggests the gut epithelium plays a basic role in immune interactions with bacteria. Contrary to other commensal strains of Escherichia coli, EcN profoundly modulates the gut barrier to elevate its resistance to microbial pathogens. The present review documents the properties of EcN that have led to the protection of gnotobiotic pigs against lethal enteric infections. This effect could be important in light of the growing number of acquired deficiencies that paralyze gut immunity in humans.

Extracellular proteins secreted by probiotic bacteria as mediators of effects that promote mucosa-bacteria interactions

During the last few years, a substantial body of scientific evidence has accumulated suggesting that certain surface-associated and extracellular components produced by probiotic bacteria could be responsible for some of their mechanisms of action. These bacterial components would be able to directly interact with the host mucosal cells; they include exopolysaccharides, bacteriocins, lipoteichoic acids and surface-associated and extracellular proteins. Extracellular proteins include proteins that are actively transported to the bacterial surroundings through the cytoplasmic membrane, as well as those that are simply shed from the bacterial surface. Compared to the other bacterial components, the interactive ability of extracellular proteins/peptides has been less extensively studied. In this review, current findings supporting an interaction between extracellular proteins/peptides produced by probiotic bacteria (strains of the genera Bifidobacterium, Lactobacillus and Escherichia) and host mucosal cells are discussed. Research needs and future trends are also considered.

Regulation of the polymeric immunoglobulin receptor in intestinal epithelial cells by Enterobacteriaceae: implications for mucosal homeostasis

The commensal microbiota of the human colon profoundly impacts host gene expression and mucosal homeostasis. Secretory IgA antibodies, which influence the composition of the intestinal microbiota and provide immunity against pathogens, are transported across intestinal epithelial cells (IEC) by the polymeric immunoglobulin receptor (pIgR). To compare the effects of different colonic bacteria on pIgR expression, the human IEC line HT-29 was stimulated with various species representing the 4 major phyla of colonic bacteria. Only bacteria from the family Enterobacteriaceae (phylum Proteobacteria) induced expression of pIgR and other target genes of bacterial pattern recognition receptors. HT-29 cells responded to purified ligands for Toll-like receptor (TLR)4 but not TLR2. Expression of pIgR and transport of IgA were significantly reduced in colons of mice deficient in the TLR adaptor MyD88, consistent with a role for TLR signaling in the regulation of pIgR by colonic bacteria. Induction of pIgR expression in HT-29 cells required NF-kappaB signaling but not MAPK signaling, in contrast to the requirement for both NF-kappaB and MAPK signaling for induction of pro-inflammatory genes. These results suggest that commensal Enterobacteriaceae may promote intestinal homeostasis by enhancing pIgR expression in IEC.

How bacteria-induced apoptosis of intestinal epithelial cells contributes to mucosal inflammation

The life cycle of an intestinal epithelial cell is terminated by apoptosis and/or cell shedding. Apoptotic deletion of epithelial cells from the intact intestinal mucosa is not accompanied by detectable inflammatory response or loss of barrier function. But increased permeability of the epithelial barrier and increased apoptotic rates of epithelial cells have been reported for patients suffering from inflammatory bowel disease. Microbiota can both induce or inhibit apoptosis of intestinal epithelial cells thus contribute to mucosal inflammation or support epithelial integrity respectively. Bacteria-mediated cytokine secretion and altered cell signalling are central to epithelial injury. Tumor necrosis factor (TNF) secreted after exposure to invasive bacteria induces both apoptosis and cell shedding. TNF is the major target gene of the transcription factor nuclear factor-kappa B with both pro- and anti-apoptotic effects. Autophagy promotes both cell survival and “autophagic” cell death. If autophagy is directed against microbes it is termed xenophagy. Inhibition of xenophagy has been shown to decrease cell survival. Endoplasmic reticulum (ER) stress causes misfolded proteins to accumulate in the ER lumen. It was suggested that ER stress and autophagy may interact within intestinal epithelial cells. Apoptosis in response to infection may be well proposed by the host to delete infected epithelial cells or could be a strategy of microbial pathogens to escape from exhausted cells to invade deeper mucosal layers for a prolonged bacterial colonization.

Probiotics: beneficial factors of the defence system

Probiotics, defined as living micro-organisms that provide a health benefit to the host when ingested in adequate amounts, have been used traditionally as food components to help the body to recover from diarrhoea. They are commonly ingested as part of fermented foods, mostly in fresh fermented dairy products. They can interact with the host through different components of the gut defence systems. There is mounting clinical evidence that some probiotics, but not all, help the defence of the host as demonstrated by either a shorter duration of infections or a decrease in the host's susceptibility to pathogens. Different components of the gut barrier can be involved in the strengthening of the body's defences: the gut microbiota, the gut epithelial barrier and the immune system. Many studies have been conducted in normal free-living subjects or in subjects during common infections like the common cold and show that some probiotic-containing foods can improve the functioning of or strengthen the body's defence. Specific probiotic foods can be included in the usual balanced diet of consumers to help them to better cope with the daily challenges of their environment.

Probiotic bacteria and intestinal epithelial barrier function

The intestinal tract is a diverse microenvironment where more than 500 species of bacteria thrive. A single layer of epithelium is all that separates these commensal microorganisms and pathogens from the underlying immune cells, and thus epithelial barrier function is a key component in the arsenal of defense mechanisms required to prevent infection and inflammation. The epithelial barrier consists of a dense mucous layer containing secretory IgA and antimicrobial peptides as well as dynamic junctional complexes that regulate permeability between cells. Probiotics are live microorganisms that confer benefit to the host and that have been suggested to ameliorate or prevent diseases including antibiotic-associated diarrhea, irritable bowel syndrome, and inflammatory bowel disease. Probiotics likely function through enhancement of barrier function, immunomodulation, and competitive adherence to the mucus and epithelium. This review summarizes the evidence about effects of the many available probiotics with an emphasis on intestinal barrier function and the mechanisms affected by probiotics.

Enterobacterial tumor colonization in mice depends on bacterial metabolism and macrophages but is independent of chemotaxis and motility

Despite promising results and increasing attention in bacterial cancer therapy, surprisingly little is known about initial tumor colonization and the interaction between bacteria and surrounding tumor tissue. Here, we analyzed the role of chemotaxis, motility, and metabolism both in Escherichia coli and Salmonella enterica serovar Typhimurium strains upon intravenous injection into tumor-bearing mice. In contrast to previous models, we found that chemotaxis and motility do not play a significant role in tumor colonization and bacterial distribution within the tumor. Rather, the whole colonization and intratumoral migration process seems to be a passive mechanism that is influenced by the reticuloendothelial system of the host, by the tumor microenvironment and by the bacterial metabolism. These conclusions were supported by experimental data demonstrating that disruption of the basic branch of the aromatic amino acid biosynthetic pathway and depletion of macrophages, in contrast to flagellar mutations, led to significant changes in bacterial accumulation in tumors of live mice.

Decisive role of lipopolysaccharide in activating nitric oxide and cytokine production by the probiotic Escherichia coli strain Nissle 1917

Effects of Gram-negative probiotic E. coli strain Nissle 1917 (EcN) on the production of nitric oxide (NO) and cytokines were determined in cultures of resident peritoneal cells of rats. The cells (2 x 10(6)/mL) were cultured for 24 h in the presence of live EcN suspension (EcN-Susp), bacteria-free supernatant of this suspension (Sup-EcN), and LPS of EcN origin (LPS-EcN). The biosynthesis of NO was substantially enhanced using live bacteria counts as low as 10(3)/mL applied in the form of EcN-Susp. The same NO-enhancing effect was produced by the correspondingly diluted Sup-EcN. It was found that Sup-EcN contained relatively high amounts of LPS. Administration of the LPS-EcN mimicked the high NO-augmenting activities of both Sup-EcN and EcN-Susp. However, the activity of LPS-EcN was significantly less pronounced than were the activities of Sup-EcN and EcN-Susp containing identical amounts of LPS. The NO-stimulatory effects of the EcN preparations were completely inhibited by polymyxin B. All LPS-EcN and correspondingly diluted Sup-EcN and EcN-Susp stimulated the secretion of cytokines TNF-alpha, IL-1beta, IL-6, IL-10 and VEGF. Also these effects were abrogated by polymyxin B. In contrast to the effects on NO production, the cytokine-stimulatory effects were significantly less pronounced after the exposure of the cells to Sup-EcN and EcN-Susp than to the identical amounts of LPS-EcN. It may be concluded that the in vitro stimulatory effects of EcN on NO and cytokine production are mediated by LPS. It is suggested that the immunostimulatory activity of LPS is modulated by EcN-derived factor(s), the nature of which remains to be identified.

Safety of probiotic Escherichia coli strain Nissle 1917 depends on intestinal microbiota and adaptive immunity of the host

Probiotics are viable microorganisms that are increasingly used for treatment of a variety of diseases. Occasionally, however, probiotics may have adverse clinical effects, including septicemia. Here we examined the role of the intestinal microbiota and the adaptive immune system in preventing translocation of probiotics (e.g., Escherichia coli Nissle). We challenged C57BL/6J mice raised under germfree conditions (GF-raised C57BL/6J mice) and Rag1(-/-) mice raised under germfree conditions (GF-raised Rag1(-/-) mice) and under specific-pathogen-free conditions (SPF-raised Rag1(-/-) mice) with probiotic E. coli strain Nissle 1917, strain Nissle 1917 mutants, the commensal strain E. coli mpk, or Bacteroides vulgatus mpk. Additionally, we reconstituted Rag1(-/-) mice with CD4(+) T cells. E. coli translocation and dissemination and the mortality of mice were assessed. In GF-raised Rag1(-/-) mice, but not in SPF-raised Rag1(-/-) mice or GF-raised C57BL/6J mice, oral challenge with E. coli strain Nissle 1917, but not oral challenge with E. coli mpk, resulted in translocation and dissemination. The mortality rate was significantly higher for E. coli strain Nissle 1917-challenged GF-raised Rag1(-/-) mice (100%; P < 0.001) than for E. coli strain Nissle 1917-challenged SPF-raised Rag1(-/-) mice (0%) and GF-raised C57BL/6J mice (0%). Translocation of and mortality due to strain E. coli Nissle 1917 in GF-raised Rag1(-/-) mice were prevented when mice were reconstituted with T cells prior to strain E. coli Nissle 1917 challenge, but not when mice were reconstituted with T cells after E. coli strain Nissle 1917 challenge. Cocolonization experiments revealed that E. coli mpk could not prevent translocation of strain E. coli Nissle 1917. Moreover, we demonstrated that neither lipopolysaccharide structure nor flagella play a role in E. coli strain Nissle 1917 translocation and dissemination. Our results suggest that if both the microbiota and adaptive immunity are defective, translocation across the intestinal epithelium and dissemination of the probiotic E. coli strain Nissle 1917 may occur and have potentially severe adverse effects. Future work should define the possibly related molecular factors that promote probiotic functions, fitness, and facultative pathogenicity.

Clinical trial: probiotic treatment of acute distal ulcerative colitis with rectally administered Escherichia coli Nissle 1917 (EcN)

BACKGROUND

Probiotics are effective in inflammatory bowel diseases. Clinical effectiveness and dose dependency of E. coli Nissle (EcN) enemas were investigated in ulcerative colitis (UC).

METHODS

In a double-blind study, 90 patients with moderate distal activity in UC were randomly assigned to treatment with either 40, 20, or 10 ml enemas (N = 24, 23, 23) containing 10E8 EcN/ml or placebo (N = 20). The study medication was taken once daily for at least 2 weeks. After 2, 4 and/or 8 weeks the clinical DAI was assessed together with tolerance to treatment. Patients who reached clinical DAI <or= 2 within that time were regarded as responders.

RESULTS

According to ITT analysis the number of responders was not significantly higher in the EcN group than in the placebo group (p = 0.4430, 2-sided). However, the Jonckheere-Terpstra rank correlation for dose-dependent efficacy indicated a significant correlation of per-protocol responder rates (p = 0.0446, 2-sided). Time to remission was shortest with EcN 40 ml, followed by EcN 20 ml. The number of adverse events did not differ notably.

CONCLUSION

In contrast to ITT analysis, efficacy of rectal EcN application was significant in PP and points to EcN as a well tolerated treatment alternative in moderate distal UC.

TRIAL REGISTRATION

German Clinical Trials Register DRK00000234.

Host interactions of probiotic bacterial surface molecules: comparison with commensals and pathogens

How can probiotic bacteria transduce their health benefits to the host? Bacterial cell surface macromolecules are key factors in this beneficial microorganism-host crosstalk, as they can interact with host pattern recognition receptors (PRRs) of the gastrointestinal mucosa. In this Review, we highlight the documented signalling interactions of the surface molecules of probiotic bacteria (such as long surface appendages, polysaccharides and lipoteichoic acids) with PRRs. Research on host-probiotic interactions can benefit from well-documented host-microorganism studies that span the spectrum from pathogenicity to mutualism. Distinctions and parallels are therefore drawn with the interactions of similar molecules that are presented by gastrointestinal commensals and pathogens.

The K5 capsule of Escherichia coli strain Nissle 1917 is important in stimulating expression of Toll-like receptor 5, CD14, MyD88, and TRIF together with the induction of interleukin-8 expression via the mitogen-activated protein kinase pathway in epithelial cells

Escherichia coli strain Nissle 1917, which has been widely used as a probiotic for the treatment of inflammatory bowel disorders, expresses a K5 capsule, the expression of which is often associated with extraintestinal and urinary tract isolates of E. coli. Previously, it had been shown that the expression of a K5 capsule by Nissle 1917 was important in mediating interactions with epithelial cells and the extent of chemokine expression. In this paper, we show that infection with Nissle 1917 induces expression of Toll-like receptor 4 (TLR4) and TLR5 in Caco-2 cells and that maximal induction of TLR5 required the K5 capsule. In addition, purified K5 polysaccharide was capable of inducing expression of TLR5 and mCD14 and potentiated the activity of both TLR4 and TLR5 agonists to increase the proinflammatory response. Infection with Nissle 1917 also increased the expression of the adaptor molecules MyD88 and TRIF, which was K5 capsule dependent. By Western blot analysis, it was possible to show that induction of interleukin-8 by Nissle 1917 was predominantly through the mitogen-activated protein (MAP) kinase pathway and that expression of the K5 capsule was important for activation of the MAP kinase pathway. This paper provides new information on the function of the K5 capsule in mediating interactions between Nissle 1917 and epithelial cells and the mechanisms that underlie the probiotic properties of Nissle 1917.

Lactobacillus delbrueckii subsp lactis (strain CIDCA 133) resists the antimicrobial activity triggered by molecules derived from enterocyte-like Caco-2 cells

AIMS

The aim of the present study was to assess the ability of a potentially probiotic strain to resist, in vitro, the effect of intestinal antimicrobial molecules.

METHODS AND RESULTS

Strain CIDCA 133 of Lactobacillus delbrueckii subsp lactis was studied. Lactobacillus delbrueckii subsp bulgaricus as well as other gram-positive and gram-negative bacteria were used for comparison purposes. The effect of different antimicrobial extracts was determined by diffusion assays, viable counts and growth kinetics. Human-defensins (h beta D1 and h beta D2) were also included in the study. Two types of cellular fractions from Caco-2 cells were tested: (i) cytosolic fractions, obtained by sonication of cultured human enterocytes and (ii) cationic fraction, obtained by batch extraction of the cytosolic fraction with a weak cation exchange resin. In addition, the effect of Caco-2-secreted factors was studied. Strain CIDCA 133 was neither inhibited by Caco-2 secreted, cytosolic nor cationic fractions. Of note, human-defensins were inactive against strain CIDCA 133. In contrast, a related lactobacilli: Lactobacilli delbrueckii subsp bulgaricus (strain CIDCA 331) and other species of gram-positive or gram-negative bacteria were strongly inhibited.

CONCLUSIONS

Strain CIDCA 133 is able to survive and grow in the presence of enterocyte-derived antimicrobial molecules. This ability is not a general property of lactobacilli.

SIGNIFICANCE AND IMPACT OF THE STUDY

Results could provide a new insight into the mechanisms of the probiotic effect and encourage further studies on this field. Resistance to antimicrobial peptides can be relevant to understand the interaction of potentially probiotic strains with the host's immune system. This ability can be also relevant as a selection criterion for new probiotic strains.

How can probiotics and prebiotics impact mucosal immunity?

The study of probiotics and prebiotics is an expanding field of interest and scientific research that has resulted in insights related to the host immune response. Recent advances have naturally led to key questions. What are the specific probiotic components that mediate immunomodulation? Can we extrapolate the results of in vitro studies in animal and human trials? Which biomarkers and immune parameters should be measured in probiotic and prebiotic intervention studies? These questions were part of a discussion entitled "How Can Probiotics and Prebiotics Impact Mucosal Immunity" at the 2009 Annual Meeting of the International Scientific Association for Probiotics and Prebiotics (ISAPP). This review highlights recent knowledge about the modulation of mucosal immunity by probiotics and prebiotics, as well as considerations for measuring their effects on mucosal immunity. A list of biomarkers and immune parameters to be measured in human clinical trials is included.

Molecular crosstalk of probiotic bacteria with the intestinal immune system: clinical relevance in the context of inflammatory bowel disease

It is current knowledge that the intestinal microbiota plays a major role in the development and maintenance of intestinal health. Intestinal epithelial cells (IEC) constitute the interface between the gut lumen and the innate and adaptive immune system. To maintain intestinal homeostasis, the organized and diffuse compartments of the gut-associated lymphoid tissue have to process the continuously varying information at the interface between the luminal side and the host. Dysregulated intestinal immune responses towards commensal bacteria are an important factor in the pathogenesis of inflammatory bowel diseases (IBD). In contrast to the colitogenic effects of enteric bacteria, clinical and experimental studies showed that specific probiotic strains are protective in the context of chronic intestinal inflammation. Although the molecular understanding of bacteria-host interaction is improving, the anti-inflammatory mechanisms induced by these probiotic bacteria are just starting to be unraveled. The present review is meant to summarize and discuss the clinical relevance of probiotics, but it also seeks to give an overview about currently known probiotic mechanisms in the context of chronic intestinal inflammation with a focus on IEC.

Horizontal gene transfer of the secretome drives the evolution of bacterial cooperation and virulence

Background

Microbes engage in a remarkable array of cooperative behaviors, secreting shared proteins that are essential for foraging, shelter, microbial warfare, and virulence. These proteins are costly, rendering populations of cooperators vulnerable to exploitation by nonproducing cheaters arising by gene loss or migration. In such conditions, how can cooperation persist?

Results

Our model predicts that differential gene mobility drives intragenomic variation in investment in cooperative traits. More mobile loci generate stronger among-individual genetic correlations at these loci (higher relatedness) and thereby allow the maintenance of more cooperative traits via kin selection. By analyzing 21 Escherichia genomes, we confirm that genes coding for secreted proteins—the secretome—are very frequently lost and gained and are associated with mobile elements. We show that homologs of the secretome are overrepresented among human gut metagenomics samples, consistent with increased relatedness at secretome loci across multiple species. The biosynthetic cost of secreted proteins is shown to be under intense selective pressure, even more than for highly expressed proteins, consistent with a cost of cooperation driving social dilemmas. Finally, we demonstrate that mobile elements are in conflict with their chromosomal hosts over the chimeric ensemble's social strategy, with mobile elements enforcing cooperation on their otherwise selfish hosts via the cotransfer of secretome genes with “mafia strategy” addictive systems (toxin-antitoxin and restriction-modification).

Conclusion

Our analysis matches the predictions of our model suggesting that horizontal transfer promotes cooperation, as transmission increases local genetic relatedness at mobile loci and enforces cooperation on the resident genes. As a consequence, horizontal transfer promoted by agents such as plasmids, phages, or integrons drives microbial cooperation.

Recent developments and perspectives in the investigation of probiotic effects

The quest for a better understanding of how probiotics work has boosted an enormous interest in the molecular processes underlying host-microbe interactions. This review covers recent developments and perspectives in the study of probiotic mechanisms.

Mechanisms of probiotic actions - A review

Probiotics are gaining more and more interest as alternatives for antibiotics or anti-inflammatory drugs. However, their mode of action is poorly understood. This review will present examples of probiotic actions from three general modes of actions into which probiotic effects can be classified. Probiotics might modulate the host's immune system, affect other microorganisms directly or act on microbial products, host products or food components. What kind of effect(s) a certain probiotic executes depends on its metabolic properties, the molecules presented at its surface or on the components secreted. Even integral parts of the bacterial cell such as its DNA or peptidoglycan might be of importance for its probiotic effectiveness. The individual combination of such properties in a certain probiotic strain determines its specific probiotic action and as a consequence its effective application for the prevention and/or treatment of a certain disease.

Influence of standard treatment on ileal and colonic antimicrobial defensin expression in active Crohn's disease

BACKGROUND

Crohn's Disease (CD), a chronic intestinal inflammation, is currently treated primarily by therapeutics which are directed against inflammatory responses. Recent findings though suggest a central role of the innate immune barrier in the pathophysiology. Important factors providing this barrier are antimicrobial peptides like the alpha- and beta-defensins. Little is known about in vivo effects of common drugs on their expression.

AIM

To analyse the influence of corticosteroids, azathioprine and aminosalicylate treatment on ileal and colonic antimicrobial peptides in active CD and also assess the role of inflammation.

METHODS

We measured the expression of antimicrobial peptides and pro-inflammatory cytokines in 75 patients with active CD.

RESULTS

Ileal and colonic alpha- and beta-defensins as well as LL37 remained unaffected by corticosteroids, azathioprine or aminosalicylate treatment. Additionally, we did not observe a negative coherency between Paneth cell alpha-defensins and any measured cytokines. HBD2 and LL37 unlike HBD1 levels were linked to inflammatory cytokines and increased in highly inflamed samples.

CONCLUSIONS

Current oral drug treatment seems to have no major effect on the expression of antimicrobial peptides. In contrast to HBD2 and LL37, ileal levels of HD5 and HD6 and colonic HBD1 level are independent of current inflammation. Innovative drugs should aim to strengthen protective innate immunity.