Shiga toxin 2 translocation across intestinal epithelium is linked to virulence of Shiga toxin-producing Escherichia coli in humans.

Shiga toxin-producing Escherichia coli (STEC) are characterized by the release of potent Shiga toxins (Stx), which are associated with severe intestinal and renal disease. Although all STEC strains produce Stx, only a few serotypes cause infection in humans. To determine which virulence traits in vitro are linked to human disease in vivo, 13 Stx2a-producing STEC strains of seropathotype (SPT) A or B (associated with severe human intestinal disease and outbreaks) and 6 strains of SPT D or E (rarely or not linked to human disease) were evaluated in a microaerobic human colonic epithelial infection model. All SPT strains demonstrated similar growth, colonization of polarized T84 colon carcinoma cells and Stx release into the medium. In contrast, Stx translocation across the T84 cell monolayer was significantly lower in SPT group DE compared to SPT group AB strains. Further experiments showed that Stx penetration occurred via a transcellular pathway and was independent of bacterial type III secretion and attaching and effacing lesion formation. These results suggest that the extent of Stx transcytosis across the gut epithelium may represent an important indicator of STEC pathogenicity for humans.

Probiotic and enterohemorrhagic Escherichia coli: An effective strategy against a deadly enemy?

Enterohemorrhagic Escherichia coli (EHEC) are major food-borne pathogens that constitute a serious public health threat. Currently, there is no specific treatment available for EHEC infections in human creating an urgent need for the development of alternative therapeutic strategies. Among them, one of the most promising approaches is the use of probiotic microorganisms. Even if many studies have shown the antagonistic effects of probiotic bacteria or yeast on EHEC survival, virulence, adhesion on intestinal epithelium or pathogen-induced inflammatory responses, mechanisms mediating their beneficial effects remain unclear. This review describes EHEC pathogenesis and novel therapeutic strategies, with a particular emphasis on probiotics. The interests and limits of a probiotic-based approach and the way it might be incorporated into global health strategies against EHEC infections will be discussed.

Increased EHEC survival and virulence gene expression indicate an enhanced pathogenicity upon simulated pediatric gastrointestinal conditions.

BACKGROUND: Enterohemorrhagic Escherichia coli (EHEC) are major foodborne pathogens that constitute a serious public health threat, mainly in young children. Shiga toxins (Stx) are the main virulence determinants of EHEC pathogenesis but adhesins like intimin (eae) and Long polar fimbriae (Lpf) also contribute to infection. The TNO GastroIntestinal Model (TIM) was used for a comparative study of EHEC O157:H7 survival and virulence under adult and child digestive conditions. METHODS: Survival kinetics in the in vitro digestive tract were determined by plating while bacterial viability was assessed by flow cytometry analysis. Expression of stx, eae, and lpf genes was followed by reverse transcriptase-quantitative PCR (RT-qPCR) and Stx production was measured by ELISA (enzyme-linked immunosorbent assay). RESULTS: Upon gastrointestinal passage, a higher amount of viable cells was found in the simulated ileal effluents of children compared to that of adults (with 34 and 6% of viable cells, respectively). Expression levels of virulence genes were up to 125-fold higher in children. Stx was detected only in child ileal effluents. CONCLUSION: Differences in digestive physicochemical parameters may partially explain why children are more susceptible to EHEC infection than adults. Such data are essential for a full understanding of EHEC pathogenesis and would help in designing novel therapeutic approaches.

Enterohemorrhagic Escherichia coli O157:H7 survival in an in vitro model of the human large intestine and interactions with probiotic yeasts and resident microbiota.

This is the first report on the fate of enterohemorrhagic Escherichia coli O157:H7 in simulated human colonic conditions. The pathogen was progressively eliminated from the bioreactor and did not modify the major populations of resident microbiota. The coadministration of the Saccharomyces cerevisiae CNCM I-3856 probiotic strain led to a significant increase in acetate production but did not reduce pathogen viability.

Specific Proteomic Identification of Collagen-Binding Proteins in Escherichia coli O157:H7: Characterisation of OmpA as a Potent Vaccine Antigen.

Escherichia coli is a versatile commensal species of the animal gut that can also be a pathogen able to cause intestinal and extraintestinal infections. The plasticity of its genome has led to the evolution of pathogenic strains, which represent a threat to global health. Additionally, E. coli strains are major drivers of antibiotic resistance, highlighting the urgent need for new treatment and prevention measures. The antigenic and structural heterogeneity of enterohaemorrhagic E. coli colonisation factors has limited their use for the development of effective and cross-protective vaccines. However, the emergence of new strains that express virulence factors deriving from different E. coli diarrhoeagenic pathotypes suggests that a vaccine targeting conserved proteins could be a more effective approach. In this study, we conducted proteomics analysis and functional protein characterisation to identify a group of proteins potentially involved in the adhesion of E. coli O157:H7 to the extracellular matrix and intestinal epithelial cells. Among them, OmpA has been identified as a highly conserved and immunogenic antigen, playing a significant role in the adhesion phenotype of E. coli O157:H7 and in bacterial aggregation. Furthermore, antibodies raised against recombinant OmpA effectively reduced the adhesion of E. coli O157:H7 to intestinal epithelial cells. The present work highlights the role of OmpA as a potent antigen for the development of a vaccine against intestinal pathogenic E. coli.

Two cases of urinary tract infection caused by Shiga toxin-producing Escherichia coli O157:H7 strains.

STEC strains can infect extra-intestinal sites such as the human urinary tract and sometimes cause severe complications. We report two cases of urinary tract infection caused by STEC in two elderly women with comorbidities. Although both strains belonged to the O157:H7 serotype and carried genes associated with severe illness, none of the patients developed hemolytic uremic syndrome (HUS). These findings provide additional evidence for the presence of these agents in our country and in the region, and highlight the need to maintain an active surveillance system of HUS cases, placing special emphasis on the study of other sites of infection in patients with non-diarrheal HUS.

AhR/IL-22 pathway as new target for the treatment of post-infectious irritable bowel syndrome symptoms.

Alterations in brain/gut/microbiota axis are linked to Irritable Bowel Syndrome (IBS) physiopathology. Upon gastrointestinal infection, chronic abdominal pain and anxio-depressive comorbidities may persist despite pathogen clearance leading to Post-Infectious IBS (PI-IBS). This study assesses the influence of tryptophan metabolism, and particularly the microbiota-induced AhR expression, on intestinal homeostasis disturbance following gastroenteritis resolution, and evaluates the efficacy of IL-22 cytokine vectorization on PI-IBS symptoms. The Citrobacter rodentium infection model in C57BL6/J mice was used to mimic Enterobacteria gastroenteritis. Intestinal homeostasis was evaluated as low-grade inflammation, permeability, mucosa-associated microbiota composition, and colonic sensitivity. Cognitive performances and emotional state of animals were assessed using several tests. Tryptophan metabolism was analyzed by targeted metabolomics. AhR activity was evaluated using a luciferase reporter assay method. One Lactococcus lactis strain carrying an eukaryotic expression plasmid for murine IL-22 (L. lactisIL-22) was used to induce IL-22 production in mouse colonic mucosa. C. rodentium-infected mice exhibited persistent colonic hypersensitivity and cognitive impairments and anxiety-like behaviors after pathogen clearance. These post-infectious disorders were associated with low-grade inflammation, increased intestinal permeability, decrease of Lactobacillaceae abundance associated with the colonic layer, and increase of short-chain fatty acids (SCFAs). During post-infection period, the indole pathway and AhR activity were decreased due to a reduction of tryptophol production. Treatment with L. lactisIL-22 restored gut permeability and normalized colonic sensitivity, restored cognitive performances and decreased anxiety-like behaviors. Data from the video-tracking system suggested an upgrade of welfare for mice receiving the L.lactisIL-22 strain. Our findings revealed that AhR/IL-22 signaling pathway is altered in a preclinical PI-IBS model. IL-22 delivering alleviate PI-IBS symptoms as colonic hypersensitivity, cognitive impairments, and anxiety-like behaviors by acting on intestinal mucosa integrity. Thus, therapeutic strategies targeting this pathway could be developed to treat IBS patients suffering from chronic abdominal pain and associated well-being disorders.

Development and evaluation of a real-time PCR assay for detection and quantification of blastocystis parasites in human stool samples: prospective study of patients with hematological malignancies.

Blastocystis anaerobic parasites are widespread worldwide in the digestive tract of many animal species, including humans. Epidemiological Blastocystis studies are often limited by the poor sensitivity of standard parasitological assays for its detection. This report presents a highly sensitive real-time quantitative PCR (qPCR) assay developed to detect Blastocystis parasites in stool samples. The assay targets a partial sequence of the Blastocystis small ribosomal subunit (SSU) rRNA gene, allowing subtyping (ST) of Blastocystis isolates by direct sequencing of qPCR products. This qPCR method was assessed in a prospective study of 186 patients belonging to two cohorts--a group of 94 immunocompromised patients presenting hematological malignancies and a control group of 92 nonimmunocompromised patients. Direct-light microscopy and xenic in vitro stool culture analysis showed only 29% and 52% sensitivity, respectively, compared to our qPCR assay. Of the 27 (14.5%) Blastocystis-positive patients, 8 (4%) experienced digestive symptoms. No correlation was found between symptomatic patients and immune status, parasite load, or parasite subtypes, although subtyping of all isolates revealed a high (63.0%) prevalence of ST4. Two unexpected avian subtypes were found, i.e., ST6 and ST7, which are frequently isolated in Asia but rarely present in Western countries. In conclusion, this qPCR proved by far the most sensitive of the tested methods and allowed subtype determination by direct sequencing of qPCR products. New diagnostic tools such as the qPCR are essential for evaluating the clinical relevance of Blastocystis subtypes and their role in acute or chronic digestive disorders.

Effect of a new probiotic Saccharomyces cerevisiae strain on survival of Escherichia coli O157:H7 in a dynamic gastrointestinal model.

Survival of Escherichia coli O157:H7 was investigated using a dynamic gastrointestinal model. A high bacterial mortality was observed in the stomach and duodenum. In contrast, bacteria grew in the distal parts of the small intestine. The coadministration of Saccharomyces cerevisiae CNCM I-3856 led to a significant reduction of bacterial resumption, maybe through ethanol production.

The Secretome landscape of Escherichia coli O157:H7: Deciphering the cell-surface, outer membrane vesicle and extracellular subproteomes.

Among diarrheagenic E. coli (DEC), enterohaemorrhagic E. coli (EHEC) are the most virulent anthropozoonotic agents. The ability of bacterial cells to functionally interact with their surrounding essentially relies on the secretion of different protein effectors. To experimentally determine the repertoire of extracytoproteins in E. coli O157:H7, a subproteomic analysis was performed not only considering the extracellular milieu but the cell surface and outer membrane vesicles. Following a secretome-based approach, the proteins trafficking from the interior to the exterior of the cell were depicted considering cognate protein transport systems and subcellular localisation. Label-free quantitative analysis of the proteosurfaceome, proteovesiculome and exoproteome from E. coli O157:H7 grown in three different nutrient media revealed differential protein expression profiles and allowed defining the core and variant subproteomes. Network analysis further revealed the higher abundance of some protein clusters in chemically defined medium over rich complex medium, especially related to some outer membrane proteins, ABC transport and Type III secretion systems. This first comprehensive study of the EHEC secretome unravels the profound influence of environmental conditions on the extracytoplasmic proteome, provides new insight in the physiology of E. coli O157:H7 and identifies potentially important molecular targets for the development of preventive strategies against EHEC/STEC. SIGNIFICANCE: Escherichia coli O157:H7 is responsible for severe diarrhoea especially in young children. Despite years of investigations, the global view of the extracytoplasmic proteins expressed in this microorganism was eluded. To provide the first comprehensive view of the secretome landscape of E. coli O157:H7, the exoproteome, proteosurfaceome and proteovesiculome were profiled using growth conditions most likely to induce changes in bacterial protein secretion. The profound influence of growth conditions on the extracytoplasmic proteome was unravelled and allowed identifying the core and variant subproteomes. Besides new insight in the physiology of enterohaemorrhagic E. coli, these proteins potentially constitute important molecular targets for the development of preventive strategies.

Molecular analysis of shiga toxin-producing Escherichia coli strains isolated from hemolytic-uremic syndrome patients and dairy samples in France.

Shiga toxin-producing Escherichia coli (STEC) has been associated with food-borne diseases ranging from uncomplicated diarrhea to hemolytic-uremic syndrome (HUS). While most outbreaks are associated with E. coli O157:H7, about half of the sporadic cases may be due to non-O157:H7 serotypes. To assess the pathogenicity of STEC isolated from dairy foods in France, 40 strains isolated from 1,130 raw-milk and cheese samples were compared with 15 STEC strains isolated from patients suffering from severe disease. The presence of genes encoding Shiga toxins (stx(1), stx(2), and variants), intimin (eae and variants), adhesins (bfp, efa1), enterohemolysin (ehxA), serine protease (espP), and catalase-peroxidase (katP) was determined by PCR and/or hybridization. Plasmid profiling, ribotyping, and pulsed-field gel electrophoresis (PFGE) were used to further compare the strains at the molecular level. A new stx(2) variant, stx(2-CH013), associated with an O91:H10 clinical isolate was identified. The presence of the stx(2), eae, and katP genes, together with a combination of several stx(2) variants, was clearly associated with human-pathogenic strains. In contrast, dairy food STEC strains were characterized by a predominance of stx(1), with a minority of isolates harboring eae, espP, and/or katP. These associations may help to differentiate less virulent STEC strains from those more likely to cause disease in humans. Only one dairy O5 isolate had a virulence gene panel identical to that of an HUS-associated strain. However, the ribotype and PFGE profiles were not identical. In conclusion, most STEC strains isolated from dairy products in France showed characteristics different from those of strains isolated from patients.

Differential biotin labelling of the cell envelope proteins in lipopolysaccharidic diderm bacteria: Exploring the proteosurfaceome of Escherichia coli using sulfo-NHS-SS-biotin and sulfo-NHS-PEG4-bismannose-SS-biotin.

Surface proteins are the major factor for the interaction between bacteria and its environment, playing an important role in infection, colonisation, virulence and adaptation. However, the study of surface proteins has proven difficult mainly due to their hydrophobicity and/or relatively low abundance compared with cytoplasmic proteins. To overcome these issues new proteomic strategies have been developed, such as cell-surface protein labelling using biotinylation reagents. Sulfo-NHS-SS-biotin is the most commonly used reagent to investigate the proteins expressed at the cell surface of various organisms but its use in lipopolysaccharidic diderm bacteria (archetypical Gram-negative bacteria) remains limited to a handful of species. While generally pass over in silence, some periplasmic proteins, but also some inner membrane lipoproteins, integral membrane proteins and cytoplasmic proteins (cytoproteins) are systematically identified following this approach. To limit cell lysis and diffusion of the sulfo-NHS-SS-biotin through the outer membrane, biotin labelling was tested over short incubation times and proved to be as efficient for 1 min at room temperature. To further limit labelling of protein located below the outer membrane, the use of high-molecular weight sulfo-NHS-PEG4-bismannose-SS-biotin appeared to recover differentially cell-envelope proteins compared to low-molecular weight sulfo-NHS-SS-biotin. Actually, the sulfo-NHS-SS-biotin recovers at a higher extent the proteins completely or partly exposed in the periplasm than sulfo-NHS-PEG4-bismannose-SS-biotin, namely periplasmic and integral membrane proteins as well as inner membrane and outer membrane lipoproteins. These results highlight that protein labelling using biotinylation reagents of different sizes provides a sophisticated and accurate way to differentially explore the cell envelope proteome of lipopolysaccharidic diderm bacteria. SIGNIFICANCE: While generally pass over in silence, some periplasmic proteins, inner membrane lipoproteins (IMLs), integral membrane proteins (IMPs) and cytoplasmic proteins (cytoproteins) are systematically identified following cell-surface biotin labelling in lipopolysaccharidic diderm bacteria (archetypal Gram-negative bacteria). The use of biotinylation molecules of different sizes, namely sulfo-NHS-SS-biotin and sulfo-NHS-PEG4-bismannose-SS-biotin, was demonstrated to provide a sophisticated and accurate way to differentially explore the cell envelope proteome of lipopolysaccharidic diderm bacteria.

Enterohemorrhagic Escherichia coli pathogenesis: role of Long polar fimbriae in Peyer's patches interactions.

Enterohemorrhagic Escherichia coli (EHEC) are major food-borne pathogens whose survival and virulence in the human digestive tract remain unclear owing to paucity of relevant models. EHEC interact with the follicle-associated epithelium of Peyer's patches of the distal ileum and translocate across the intestinal epithelium via M-cells, but the underlying molecular mechanisms are still unknown. Here, we investigated the involvement of Long polar fimbriae (Lpf) in EHEC pathogenesis. Of the 236 strains tested, a significant association was observed between the presence of lpf operons and pathogenicity. In sophisticated in vitro models of the human gastro-intestinal tract, lpf expression was induced during transit through the simulated stomach and small intestine, but not in the colonic compartment. To investigate the involvement of Lpf in EHEC pathogenesis, lpf isogenic mutants and their relative trans-complemented strains were generated. Translocation across M-cells, interactions with murine ileal biopsies containing Peyer's patches and the number of hemorrhagic lesions were significantly reduced with the lpf mutants compared to the wild-type strain. Complementation of lpf mutants fully restored the wild-type phenotypes. Our results indicate that (i) EHEC might colonize the terminal ileum at the early stages of infection, (ii) Lpf are an important player in the interactions with Peyer's patches and M-cells, and could contribute to intestinal colonization.

A secretome view of colonisation factors in Shiga toxin-encoding Escherichia coli (STEC): from enterohaemorrhagic E. coli (EHEC) to related enteropathotypes.

Shiga toxin-encoding Escherichia coli (STEC) regroup strains that carry genes encoding Shiga toxin (Stx). Among intestinal pathogenic E. coli, enterohaemorrhagic E. coli (EHEC) constitute the major subgroup of virulent STEC. EHEC cause serious human disease such as haemorrhagic colitis and haemolytic-uremic syndrome. While EHEC have evolved from enteropathogenic E. coli, hybrids with enteroaggregative E. coli have recently emerged. Of note, some enteroinvasive E. coli also belong to the STEC group. While the LEE (locus of enterocyte effacement) is a key and prominent molecular determinant in the pathogenicity, neither all EHEC nor STEC contain the LEE, suggesting that they possess additional virulence and colonisation factors. Currently, nine protein secretion systems have been described in diderm-lipopolysaccharide bacteria (archetypal Gram-negative) and can be involved in the secretion of extracellular effectors, cell-surface proteins or assembly of cell-surface organelles, such as flagella or pili. In this review, we focus on the secretome of STEC and related enteropathotypes, which are relevant to the colonisation of biotic and abiotic surfaces. Considering the wealth of potential protein trafficking mechanisms, the different combinations of colonisation factors and modulation of their expression is further emphasised with regard to the ecophysiology of STEC.

Dynamic In Vitro Models of the Human Gastrointestinal Tract as Relevant Tools to Assess the Survival of Probiotic Strains and Their Interactions with Gut Microbiota.

The beneficial effects of probiotics are conditioned by their survival during passage through the human gastrointestinal tract and their ability to favorably influence gut microbiota. The main objective of this study was to use dynamic in vitro models of the human digestive tract to investigate the effect of fasted or fed state on the survival kinetics of the new probiotic Saccharomyces cerevisiae strain CNCM I-3856 and to assess its influence on intestinal microbiota composition and activity. The probiotic yeast showed a high survival rate in the upper gastrointestinal tract whatever the route of admistration, i.e., within a glass of water or a Western-type meal. S. cerevisiae CNCM I-3856 was more sensitive to colonic conditions, as the strain was not able to colonize within the bioreactor despite a twice daily administration. The main bacterial populations of the gut microbiota, as well as the production of short chain fatty acids were not influenced by the probiotic treatment. However, the effect of the probiotic on the gut microbiota was found to be individual dependent. This study shows that dynamic in vitro models can be advantageously used to provide useful insight into the behavior of probiotic strains in the human digestive environment.

In vitro adhesion properties of Shiga toxin-producing Escherichia coli isolated from cattle, food, and humans.

Shiga toxin-producing Escherichia coli (STEC) are able to cause serious illnesses ranging from diarrhea to hemorrhagic colitis and hemolytic-uremic syndrome (HUS). These bacteria colonize the digestive tract of humans and produce Shiga-toxins, which are considered to be essential for virulence and are crucial in lethal infection. Colon colonization is supposed to be a determinant step in the development of the infection, but the virulence traits that mediate this step are unclear. We analyzed the ability of 256 STEC strains belonging to seropathotype A (the most virulent O157:H7 serotype) to seropathotype E (not involved in human disease) to adhere to HEp-2, HCT-8, and T84 cell lines. Of the 256 STEC tested most (82%) were non-adherent in our assays. The adhesion levels were globally low and were not related to pathogenicity, although the highest levels were associated to O26:H11 and O103:H2 strains of seropathotype B (associated with HUS but less commonly than serotype O157:H7), possessing both the eae and toxB genes.

Survival of Escherichia coli O26:H11 exceeds that of Escherichia coli O157:H7 as assessed by simulated human digestion of contaminated raw milk cheeses.

Shiga toxin producing Escherichia coli (STEC) are an important cause of human foodborne outbreaks. The consumption of raw milk dairy products may be an important route of STEC infection. For successful foodborne transmission, STEC strains must survive stress conditions met during gastrointestinal transit in humans. The aim of this study was to evaluate the survival of two STEC strains of serotypes O157:H7 and O26:H11 during simulated human digestion in the TNO gastro-Intestinal tract Model (TIM) of contaminated uncooked pressed cheeses. The survival of cheese microflora during in vitro gastrointestinal transit was also determined for the first time. The level of STEC increased from 2 log10 CFU/ml to 4 log10 CFU/g during the first 24h of cheese making and remained stable at around 4 log10 CFU/g during cheese ripening and conservation. During transit through the artificial stomach and duodenum, levels of STEC decreased: 0.2% of E. coli O157:H7 and 1.8% of E. coli O26:H11 were recovered at 150 min in the gastric compartment, compared with 14.3% for the transit marker. Bacterial resumption was observed in the jejunum and ileum: 35.8% of E. coli O157:H7 and 663.2% of E. coli O26:H11 were recovered at 360 min in the ileal compartment, compared with 12.6% for the transit marker. The fate of STEC was strain-dependent, the survival of E. coli O26:H11 being 13 times greater than that of E. coli O157:H7 at the end of digestion in the cumulative ileal deliveries. These data provide a better understanding of STEC behavior during gastrointestinal transit in humans after ingestion of contaminated cheese.

Blastocystis is associated with decrease of fecal microbiota protective bacteria: comparative analysis between patients with irritable bowel syndrome and control subjects.

Blastocystis is a protistan parasite living in the digestive tract of many animals, including humans. This highly prevalent intestinal parasite is suspected to be linked to Irritable Bowel Syndrome (IBS), a chronic functional bowel disorder. Here, we first compared the prevalence of Blastocystis among 56 IBS patients (40 IBS with constipation (IBS-C), 9 IBS with diarrhea (IBS-D), 4 mixed IBS (IBS-M) and 3 unsubtyped IBS (IBS-U) according to the Rome III criteria) and 56 control (i.e. without any diagnosed chronic or acute gastrointestinal disorder) subjects. The highest prevalence of Blastocystis spp. was observed in the IBS group, but was only statistically significant in men (36.8% in the IBS group versus 4.8% in the control group). We then conducted a meta-analysis including epidemiological studies attempting to determine whether Blastocystis carriage could be linked to IBS, and highlighted that IBS patients had a relative risk of 2.34 to be infected by Blastocystis when compared to non-IBS subjects. We also looked for Dientamoeba fragilis, which is often associated with IBS, and identified this parasite only in some IBS patients (n = 6/56). Several studies provided evidence for a major role of the gut microbiota in the pathophysiology of IBS. Thus, we investigated the possible impact of Blastocystis carriage on the enteric bacterial community through quantification of 8 major bacterial groups from the enteric flora. Our data indicated that men with IBS-C had a significant decrease in Bifidobacterium sp. when infected by Blastocystis. Interestingly, in control subjects (i.e. without any gastrointestinal disorder) positive for Blastocystis, Faecalibacterium prausnitzii, which is known for its anti-inflammatory properties, was significantly decreased in men. Our results support the hypothesis that Blastocystis might be linked to the pathophysiology of IBS-C and intestinal flora imbalance.

Relevance and challenges in modeling human gastric and small intestinal digestion.

Gastric and small intestinal (GSI) models are increasingly used as an alternative to in vivo assays to answer many questions raised by industry and researchers. A broad range of in vitro systems is available, from static monocompartmental to dynamic multicompartmental models. However, these models require a compromise between technological complexity and biological significance. Further efforts and technological innovations are still needed to improve in vitro models and meet growing demands in the areas of nutrition and health. This review describes the models available to date for the human stomach and small intestine and highlights their relevance in nutritional, toxicological, pharmaceutical, and microbiological studies. Limitations and challenges facing artificial digestion technology are also discussed.

Interactions with M cells and macrophages as key steps in the pathogenesis of enterohemorrhagic Escherichia coli infections.

Enterohemorrhagic Escherichia coli (EHEC) are food-borne pathogens that can cause serious infections ranging from diarrhea to hemorrhagic colitis (HC) and hemolytic-uremic syndrome (HUS). Translocation of Shiga-toxins (Stx) from the gut lumen to underlying tissues is a decisive step in the development of the infection, but the mechanisms involved remain unclear. Many bacterial pathogens target the follicle-associated epithelium, which overlies Peyer's patches (PPs), cross the intestinal barrier through M cells and are captured by mucosal macrophages. Here, translocation across M cells, as well as survival and proliferation of EHEC strains within THP-1 macrophages were investigated using EHEC O157:H7 reference strains, isogenic mutants, and 15 EHEC strains isolated from HC/HUS patients. We showed for the first time that E. coli O157:H7 strains are able to interact in vivo with murine PPs, to translocate ex vivo through murine ileal mucosa with PPs and across an in vitro human M cell model. EHEC strains are also able to survive and to produce Stx in macrophages, which induce cell apoptosis and Stx release. In conclusion, our results suggest that the uptake of EHEC by M cells and underlying macrophages in the PP may be a critical step in Stx translocation and release in vivo. A new model for EHEC infection in humans is proposed that could help in a fuller understanding of EHEC-associated diseases.