Adhesion of enteroaggregative Escherichia coli to pediatric intestinal mucosa in vitro

Shiga toxin production and translocation during microaerobic human colonic infection with Shiga toxin-producing E. coli O157:H7 and O104:H4

Haemolytic uraemic syndrome caused by Shiga toxin-producing E. coli (STEC) is dependent on release of Shiga toxins (Stxs) during intestinal infection and subsequent absorption into the bloodstream. An understanding of Stx-related events in the human gut is limited due to lack of suitable experimental models. In this study, we have used a vertical diffusion chamber system with polarized human colon carcinoma cells to simulate the microaerobic (MA) environment in the human intestine and investigate its influence on Stx release and translocation during STEC O157:H7 and O104:H4 infection. Stx2 was the major toxin type released during infection. Whereas microaerobiosis significantly reduced bacterial growth as well as Stx production and release into the medium, Stx translocation across the epithelial monolayer was enhanced under MA versus aerobic conditions. Increased Stx transport was dependent on STEC infection and occurred via a transcellular pathway other than macropinocytosis. While MA conditions had a similar general effect on Stx release and absorption during infection with STEC O157:H7 and O104:H4, both serotypes showed considerable differences in colonization, Stx production, and Stx translocation which suggest alternative virulence strategies. Taken together, our study suggests that the MA environment in the human colon may modulate Stx-related events and enhance Stx absorption during STEC infection.

Inflammatory diarrhea due to enteroaggregative Escherichia coli: evidence from clinical and mice model studies

BACKGROUND

This study was conducted to determine the role of enteroaggregative Escherichia coli (EAEC) in inflammatory diarrhea among hospitalized patients in Kolkata. The inflammatory pathogenesis of EAEC was established in mice model and histopathological studies. Presence of fecal leucocytes (FLCs) can be suspected for EAEC infection solely or as a mixed with other enteric pathogens.

METHODS

Active surveillance was conducted for 2 years on 2 random days per week with every 5th patient admitted to the Infectious Diseases Hospital (IDH). Diarrheal samples were processed by conventional culture, microscopy, ELISA and molecular methods. Two EAEC isolated as sole pathogens were examined in mice after induced intestinal infection. The intestinal tissue samples were processed to analyze the histological changes.

RESULTS

Of the 2519 samples screened, fecal leucocytes, erythrocytes and occult blood were detected in 1629 samples. Most of the patients had acute watery diarrhea (75%) and vomiting (78%). Vibrio cholerae O1 was the main pathogen in patients of 5-10 years age group (33%). Shigellosis was more in children from 2-5 years of age (19%), whereas children <2 years appeared to be susceptible for infection caused by EAEC (16%). When tested for the pathogenicity, the EAEC strains colonized well and caused inflammatory infection in the gut mucosa of BALB/C mice.

CONCLUSION

This hospital-based surveillance revealed prevalence of large number of inflammatory diarrhea. EAEC was the suspected pathogen and <2 years children appeared to be the most susceptible age group. BALB/C mice may be a suitable animal model to study the EAEC-mediated pathogenesis.

Recent advances in understanding enteric pathogenic Escherichia coli

Although Escherichia coli can be an innocuous resident of the gastrointestinal tract, it also has the pathogenic capacity to cause significant diarrheal and extraintestinal diseases. Pathogenic variants of E. coli (pathovars or pathotypes) cause much morbidity and mortality worldwide. Consequently, pathogenic E. coli is widely studied in humans, animals, food, and the environment. While there are many common features that these pathotypes employ to colonize the intestinal mucosa and cause disease, the course, onset, and complications vary significantly. Outbreaks are common in developed and developing countries, and they sometimes have fatal consequences. Many of these pathotypes are a major public health concern as they have low infectious doses and are transmitted through ubiquitous mediums, including food and water. The seriousness of pathogenic E. coli is exemplified by dedicated national and international surveillance programs that monitor and track outbreaks; unfortunately, this surveillance is often lacking in developing countries. While not all pathotypes carry the same public health profile, they all carry an enormous potential to cause disease and continue to present challenges to human health. This comprehensive review highlights recent advances in our understanding of the intestinal pathotypes of E. coli.

Persistent diarrhea: still a serious public health problem in developing countries

Diarrhea is still responsible for high rates of morbidity and mortality in children under 5 years of age. The prolongation of the acute episode may cause digestive and absorptive malfunction and, consequently, malnutrition, raising the risk of death. The objective of this review is to supply the most recent knowledge in the field of persistent diarrhea and to contribute to the decrease of its incidence. Some possible etiologic agents may be involved, including viruses, bacteria, and parasites. Treatment must be addressed to avoid malabsorption of the nutrients of the diet, associated with replacement of the hydroelectrolytic losses, to prevent its prolongation. In the great majority of the episodes, antibiotics are not indicated. Breastfeeding, introduction of safe dietary strategies to prevent protein-energy malnutrition, and improvement of sanitary conditions and hygiene are measures to be promoted with the objective of decreasing the morbidity/mortality of the diarrheic disease in children less than 5 years of age.

Shiga toxin-producing Escherichia coli O104:H4: an emerging pathogen with enhanced virulence

Pathogenic Escherichia coli are genetically diverse and encompass a broad variety of pathotypes, such as enteroaggregative E. coli (EAEC) or enterohemorrhagic E. coli (EHEC), which cause distinct clinical syndromes. The historically large 2011 German outbreak of hemolytic uremic syndrome (HUS), caused by a Shiga-toxin producing E. coli (STEC) of the serotype O104:H4, illustrated the emerging importance of non-O157 STEC. STEC O104:H4, with features characteristic of both enteroaggregative E. coli and enterohemorrhagic E. coli, represents a unique and highly virulent pathotype. The German outbreak both allowed for the evaluation of several potential therapeutic approaches to STEC-induced HUS and emphasizes the importance of early and specific detection of both O157 and non-O157 STEC.

Clostridium difficile modulates host innate immunity via toxin-independent and dependent mechanism(s)

Clostridium difficile infection (CDI) is the leading cause of hospital and community-acquired antibiotic-associated diarrhoea and currently represents a significant health burden. Although the role and contribution of C. difficile toxins to disease pathogenesis is being increasingly understood, at present other facets of C. difficile-host interactions, in particular, bacterial-driven effects on host immunity remain less studied. Using an ex-vivo model of infection, we report that the human gastrointestinal mucosa elicits a rapid and significant cytokine response to C. difficile. Marked increase in IFN-γ with modest increase in IL-22 and IL-17A was noted. Significant increase in IL-8 suggested potential for neutrophil influx while presence of IL-12, IL-23, IL-1β and IL-6 was indicative of a cytokine milieu that may modulate subsequent T cell immunity. Majority of C. difficile-driven effects on murine bone-marrow-derived dendritic cell (BMDC) activation were toxin-independent; the toxins were however responsible for BMDC inflammasome activation. In contrast, human monocyte-derived DCs (mDCs) released IL-1β even in the absence of toxins suggesting host-specific mediation. Infected DC-T cell crosstalk revealed the ability of R20291 and 630 WT strains to elicit a differential DC IL-12 family cytokine milieu which culminated in significantly greater Th1 immunity in response to R20291. Interestingly, both strains induced a similar Th17 response. Elicitation of mucosal IFN-γ/IL-17A and Th1/Th17 immunity to C. difficile indicates a central role for this dual cytokine axis in establishing antimicrobial immunity to CDI.

Animal models of enteroaggregative Escherichia coli infection

Enteroaggregative Escherichia coli (EAEC) has been acknowledged as an emerging cause of gastroenteritis worldwide for over two decades. Epidemiologists are revealing the role of EAEC in diarrheal outbreaks as a more common occurrence than ever suggested before. EAEC induced diarrhea is most commonly associated with travelers, children and immunocompromised individuals however its afflictions are not limited to any particular demographic. Many attributes have been discovered and characterized surrounding the capability of EAEC to provoke a potent pro-inflammatory immune response, however cellular and molecular mechanisms underlying initiation, progression and outcomes are largely unknown. This limited understanding can be attributed to heterogeneity in strains and the lack of adequate animal models. This review aims to summarize current knowledge about EAEC etiology, pathogenesis and clinical manifestation. Additionally, current animal models and their limitations will be discussed along with the value of applying systems-wide approaches such as computational modeling to study host-EAEC interactions.

Cryptopatches are essential for the development of human GALT

Abnormal gut-associated lymphoid tissue (GALT) in humans is associated with infectious and autoimmune diseases, which cause dysfunction of the gastrointestinal (GI) tract immune system. To aid in investigating GALT pathologies in vivo, we bioengineered a human-mouse chimeric model characterized by the development of human GALT structures originating in mouse cryptopatches. This observation expands our mechanistic understanding of the role of cryptopatches in human GALT genesis and emphasizes the evolutionary conservation of this developmental process. Immunoglobulin class switching to IgA occurs in these GALT structures, leading to numerous human IgA-producing plasma cells throughout the intestinal lamina propria. CD4+ T cell depletion within GALT structures results from HIV infection, as it does in humans. This human-mouse chimeric model represents the most comprehensive experimental platform currently available for the study and for the preclinical testing of therapeutics designed to repair disease-damaged GALT.

Adhesion of Diarrheagenic Escherichia coli and Inhibition by Glycocompounds Engaged in the Mucosal Innate Immunity

Escherichia coli colonizes the human intestine shortly after birth, with most strains engaging in a commensal relationship. However, some E. coli strains have evolved toward acquiring genetic traits associated with virulence. Currently, five categories of enteroadherent E. coli strains are well-recognized, and are classified in regard to expressed adhesins and the strategy used during the colonization. The high morbidity associated with diarrhea has motivated investigations focusing on E. coli adhesins, as well on factors that inhibit bacterial adherence. Breastfeeding has proved to be the most effective strategy for preventing diarrhea in children. Aside from the immunoglobulin content, glycocompounds and oligosaccharides in breast milk play a critical role in the innate immunity against diarrheagenic E. coli strains. This review summarizes the colonization factors and virulence strategies exploited by diarrheagenic E. coli strains, addressing the inhibitory effects that oligosaccharides and glycocompounds, such as lactoferrin and free secretory components, exert on the adherence and virulence of these strains. This review thus provides an overview of experimental data indicating that human milk glycocompounds are responsible for the universal protective effect of breastfeeding against diarrheagenic E. coli pathotypes.

Virulence of the Shiga toxin type 2-expressing Escherichia coli O104:H4 German outbreak isolate in two animal models

In May 2011, a large food-borne outbreak was traced to an unusual O104:H4 enteroaggregative Escherichia coli (EAEC) strain that produced Shiga toxin (Stx) type 2 (Stx2). We developed a mouse model to study the pathogenesis and treatment for this strain and examined the virulence of the isolate for Dutch belted rabbits. O104:H4 strain C227-11 was gavaged into C57BL/6 mice at 10(9) to 10(11) CFU/animal. The infected animals were then given water with ampicillin (Amp; 5 g/liter) ad libitum. The C227-11-infected, Amp-treated C57BL/6 mice exhibited both morbidity and mortality. Kidneys from mice infected with C227-11 showed acute tubular necrosis, a finding seen in mice infected with typical Stx-producing E. coli. We provided anti-Stx2 antibody after infection and found that all of the antibody-treated mice gained more weight than untreated mice and, in another study, that all of the antibody-treated animals lived, whereas 3/8 phosphate-buffered saline-treated mice died. We further compared the pathogenesis of C227-11 with that of an Stx-negative (Stx(-)) O104:H4 isolate, C734-09, and an Stx2(-) phage-cured derivative of C227-11. Whereas C227-11-infected animals lost weight or gained less weight over the course of infection and died, mice infected with either of the Stx(-) isolates did not lose weight and only one mouse died. When the Stx-positive (Stx(+)) and Stx2(-) O104:H4 strains were compared in rabbits, greater morbidity and mortality were observed in rabbits infected with the Stx2(+) isolates than the Stx2(-) isolates. In conclusion, we describe two animal models for EAEC pathogenesis, and these studies show that Stx2 is responsible for most of the virulence observed in C227-11-infected mice and rabbits.

Enteroaggregative Escherichia coli and acute diarrhea in children: a meta-analysis of South Asian populations

The purpose of this investigation was to evaluate the association of enteroaggregative Escherichia coli (EAEC) with acute diarrhea in children of South Asian populations. Our meta-analysis included 18 studies published between 1989 and 2011. The odds ratio (OR) was used to evaluate all available observational epidemiology studies. Modifying effects on the overall OR were approached with outlier, subgroup, cumulative, and cumulative recursive analyses. Synthesis of the 18 observational studies revealed an association between EAEC carriage and acute diarrhea, with an overall OR of 1.51, which was significant (p = 0.008), heterogeneous (Pheterogeneity < 0.0001), and unaffected by outlier analysis. This analysis, however, affected the subgroups by eliminating the following: (i) heterogeneity (from Pheterogeneity < 0.0001 to 0.30-0.72) of pooled ORs in the underpowered (OR 1.37, p = 0.15), Indian (OR 1.92, p = 0.09), and hospital-based (OR 1.66, p = 0.06) studies; (ii) non-significance of these three subgroups (OR 1.56-2.01, p < 0.0001-0.003); (iii) significance of the high-powered studies (from OR 1.70, p = 0.02 to OR 1.15, p = 0.28); (iv) heterogeneity (from Pheterogeneity < 0.0001-0.0002 to 0.11-0.15) of pooled ORs in period three (OR 1.85, p = 0.14), population-based (OR 1.36, p = 0.09), and pCVD432 (OR 1.53, p = 0.07) studies. In general, outlier treatment increased precision with the narrowing of confidence intervals, overall, and in the subgroups. Cumulative meta-analysis generally resulted in increases in the frequencies of significant effects and of heterogeneity. This meta-analysis on observational studies suggests that the association between EAEC and acute diarrhea in children is that of increased risk. This effect generally comes from heterogeneous studies of South Asian populations, but is modified with outlier and subgroup treatments.

Enteroaggregative Escherichia coli pathotype: a genetically heterogeneous emerging foodborne enteropathogen

Until now, a common feature that defines the enteroaggregative Escherichia coli (EAEC) strains is the ability to produce a 'stacked-brick' appearance on epithelial cells, but it does not distinguish between pathogenic and nonpathogenic strains. Numerous adhesins, toxins, and proteins associated with virulence have been described, as well as multiple factors contributing to EAEC-induced inflammation. None of these factors are found in all EAEC isolates, and no single factor has ever been implicated in EAEC virulence. The European outbreak of Shiga-toxin-producing EAEC raises its pathogenic potential and interest on finding the true pathogenic factors that may define this pathotype. EAEC were first associated with persistent diarrhea in infants from developing countries, since then they have increasingly been linked as a cause of acute and persistent diarrhea in young infants and children in developing and industrialized countries, individuals infected with human immunodeficiency virus, as a cause of acute diarrhea in travelers from industrialized regions, and with foodborne outbreaks. A major effect of EAEC infection is on the malnourished children in developing countries. Here, we will discuss the EAEC public health relevance and their complexity because of the strain heterogeneity regarding their pathogenesis, identification, diagnosis, lineage, epidemiology, and clinical manifestations.

Enteroaggregative Escherichia coli induced increase in intracellular calcium concentration modulates cytoskeletal F-actin rearrangement and bacterial entry in INT-407 cells

BACKGROUND

Enteroaggregative Escherichia coli (EAEC) is an emerging enteric pathogen, associated with cases of acute and persistent diarrhoea worldwide. The pathogenesis of EAEC is yet to be understood. In intestinal epithelium, an increase in [Ca²⁺](i) has been attributed due to the action of different enteric pathogens. EAEC was shown to increase [Ca²⁺](i) in HEp-2 cells.The present study was undertaken to investigate the effect of EAEC induced increase in [Ca²⁺](i) oncultured human intestinal epithelial cells.

METHODS

INT-407 cells were infected with EAEC (T8 strain) in the absence and presence of dantrolene (inhibitor of release of Ca²⁺ from intracellular stores)/verapamil (L-type Ca²⁺ channel blocker)/BAPTAAM (Ca²⁺ chelator)/U73122 (PLC inhibitor)/Cytochalasin-D (inhibitor of actin polymerization). [Ca²⁺](i) was estimated using Fura-2/AM. Cytoskeletal rearrangement was assessed by F-actin staining using TRITC-phalloidin. The invasiveness of EAEC-T8 to INT-407 cells was checked by electron microscopy and invasion assay.

RESULTS

A significant increase in [Ca²⁺](i) was observed in EAEC-T8 infected INT-407 cells, which was reduced in presence of dantrolene/verapamil/U73122. EAEC-T8 could induce cytoskeletal F-actin polymerization in INT-407 cells and was found to be invasive in nature. The cytoskeletal rearrangement as well as invasion of EAEC-T8 was attenuated in presence of U73122/dantrolene/BAPTA-AM/verapamil/cytochalasin D.

CONCLUSIONS

EAEC induced increase in [Ca²⁺](i) seems to play a major role in host cytoskeletal F-actin rearrangements leading to invasion of the organism.

GENERAL SIGNIFICANCE

Our study undoubtedly will lead to an improved understanding of EAEC-pathogenesis.

Adherence of enteroaggregative Escherichia coli to the ileal and colonic mucosa: an in vitro study utilizing the scanning electron microscopy

CONTEXT

Enteroaggregative Escherichia coli strains have been associated with persistent diarrhea in several developing countries. In vivo procedures with animal models, in vitro assays with cellular lines and in vitro organ culture with intestinal fragments have been utilized to study these bacteria and their pathogenicity.

OBJECTIVE

The present experimental research assessed the pathogenic interactions of three enteroaggregative Escherichia coli strains, using the in vitro organ culture, in order to show the adherence to different regions of both, the ileal and the colonic mucosa and demonstrate possible mechanisms that could have the participation in the prolongation of diarrheiogenic process.

METHODS

This study used intestinal fragments from terminal ileum and colon that were excised from pediatric patients undergoing intestinal surgeries and from adult patients that underwent to colonoscopic procedures. Each strain was tested with three intestinal fragments for each region. Tissue was fixed for scanning electron microscopic analysis.

RESULTS

These bacteria colonized ileal and colonic mucosa in the typical stacked-brick configuration in the ileum and colon. In both regions, the strains were seen over a great amount of mucus and sometimes over the intact epithelium. In some regions, there is a probable evidence of effacement of the microvilli. It was possible to see adhered to the intestinal surface, bacteria fimbrial structures that could be responsible for the adherence process.

CONCLUSION

In order to cause diarrhea, enteroaggregative Escherichia coli strains adhere to the intestinal mucosa, create a mucoid biofilm on the small bowel surface that could justify the digestive-absorptive abnormalities and consequently, prolonging the diarrhea.

Enteroaggregative Escherichia coli promotes transepithelial migration of neutrophils through a conserved 12-lipoxygenase pathway

Enteroaggregative Escherichia coli (EAEC) induces release of pro-inflammatory markers and disruption of intestinal epithelial barriers in vitro, suggesting an inflammatory aspect to EAEC infection. However, the mechanisms underlying EAEC-induced mucosal inflammatory responses and the extent to which these events contribute to pathogenesis is not well characterized. Employing an established in vitro model we demonstrated that EAEC prototype strain 042 induces migration of polymorphonuclear neutrophils (PMNs) across polarized T84 cell monolayers. This event was mediated through a conserved host cell signalling cascade involving the 12/15-LOX pathway and led to apical secretion of an arachidonic acid-derived lipid PMN chemoattractant, guiding PMNs across the epithelia to the site of infection. Moreover, supporting the hypothesis that inflammatory responses may contribute to EAEC pathogenesis, we found that PMN transepithelial migration promoted enhanced attachment of EAEC 042 to T84 cells. These findings suggest that EAEC-induced PMN infiltration may favour colonization and thus pathogenesis of EAEC.

Pathophysiology of enteroaggregative Escherichia coli infection: an experimental model utilizing transmission electron microscopy

CONTEXT

Enteroaggregative Escherichia coli strains have been associated with persistent diarrhea in several developing countries. In vivo procedures with animal models as rat, rabbit and gnotobiotic piglets intestinal loops, in vitro assays with cellular lines like T84, Caco 2, HT29, HeLa e HEp-2 and in vitro organ culture with intestinal fragments have been applied to study these bacteria and their pathogenicity.

OBJECTIVES

The present experimental research assessed the pathogenic interactions of three enteroaggregative Escherichia coli strains, using the in vitro organ culture, in order to observe and compare alterations in different regions of both, the ileal and the colonic mucosa.

METHODS

This study applied intestinal fragments from terminal ileum and colon that were excised from pediatric and adult patients that underwent colonoscopic procedures. Tissue was fixed for transmission electron microscopic study. Each bacterium was tested with three intestinal fragments for each region.

RESULTS

Enteroaggregative Escherichia coli strains colonized and provoked citotoxic effects in the ileal and colonic mucosa. Total or partial villi destruction, vacuolization of basal cytoplasm of the enterocytes, epithelium detachment, derangement of the structure and epithelial cell extrusion in ileal mucosa could explain the perpetuation of the diarrhea. Bacterial aggregates were seen in intestinal lumen associated with mucus and cellular debris and in the intercellular spaces of the destroyed epithelium, suggesting bacterial invasion that seemed to be secondary to the destruction of the tissue.

CONCLUSIONS

Pathogenesis of persistent diarrhea should include alterations in the small bowel structures where the digestive-absorptive functions take place. In the colonic mucosa the inflammatory lesions could explain the occurrence of colitis.

Conversion of commensal Escherichia coli K-12 to an invasive form via expression of a mutant histone-like protein

The HUα^{E38K, V42L} mutant of the bacterial histone-like protein HU causes a major change in the transcription profile of the commensal organism Escherichia coli K-12 (Kar S, Edgar R, Adhya S, Proc. Natl. Acad. Sci. U. S. A. 102:16397–16402, 2005). Among the upregulated genes are several related to pathogenic interactions with mammalian cells, as evidenced by the expression of curli fibers, Ivy, and hemolysin E. When E. coli K-12/ HUα^{E38K, V42L} was added to Int-407 cells, there was host cell invasion, phagosomal disruption, and intracellular replication. The invasive trait was also retained in a murine ileal loop model and intestinal explant assays. In addition to invasion, the internalized bacteria caused a novel subversion of host cell apoptosis through modification and regulation of the BH3-only proteins Bim_EL and Puma. Changes in the transcription profile were attributed to positive supercoiling of DNA leading to the altered availability of relevant promoters. Using the E. coli K-12/HUα^{E38K, V42L} variant as a model, we propose that traditional commensal E. coli can adopt an invasive lifestyle through reprogramming its cellular transcription, without gross genetic changes.

Escherichia coli K-12 is well established as a benign laboratory strain and a human intestinal commensal. Recent evidences, however, indicate that the typical noninvasive nature of resident E. coli can be reversed under specific circumstances even in the absence of any major genomic flux. We previously engineered an E. coli strain with a mutant histone-like protein, HU, which exhibited significant changes in nucleoid organization and global transcription. Here we showed that the changes induced by the mutant HU have critical functional consequences: from a strict extracellular existence, the mutant E. coli adopts an almost obligate intracellular lifestyle. The internalized E. coli exhibits many of the prototypical characteristics of traditional intracellular bacteria, like phagosomal escape, intracellular replication, and subversion of host cell apoptosis. We suggest that E. coli K-12 can switch between widely divergent lifestyles in relation to mammalian host cells by reprogramming its cellular transcription program and without gross changes in its genomic content.

Effect of probiotic bacterial strains of Lactobacillus, Bifidobacterium, and Enterococcus on enteroaggregative Escherichia coli

The effects of nine probiotic strains of Lactobacillus, Bifidobacterium, and Enterococcus on the growth, adhesion activity, and biofilm formation of enteroaggregative Escherichia coli (EAggEC) were examined. The culture supernatant of the E. faecium strain, with or without pH adjustment to a neutral pH, had a strong bactericidal effect on EAggEC, including induction of membrane damage and cell lysis. Supernatants of the L. casei ss. casei and L. casei ss. rhamnosus strains also had a bactericidal effect on EAggEC, but this activity was abolished by pH adjustment to a neutral pH. No inhibitory effect of the culture supernatants of Bifidobacterium or E. faecalis strains was detected. Adhesion of EAggEC to intestinal epithelial cells was not inhibited by the bacterial strains tested. Two strains of L. casei enhanced EAggEC biofilm formation, which was characterized by increased bacterial proliferation. These results suggest that the three different bacterial species; Lactobacillus, Bifidobacterium, and Enterococcus, have different effects on EAggEC, and that further analysis is required for the practical use of these bacteria as probiotics against EAggEC infection.

Aberrant response to commensal Bacteroides thetaiotaomicron in Crohn's disease: an ex vivo human organ culture study

BACKGROUND

Human ex vivo evidence indicating that an inappropriate immune response(s) to nonpathogenic bacteria contributes to disease pathogenesis in pediatric Crohn's disease (CD) is limited. The aim of the present study was to compare and contrast the early innate immune response of pediatric "healthy" versus CD mucosa to pathogenic, probiotic, and commensal bacteria.

METHODS

"Healthy control" and CD pediatric mucosal biopsies (terminal ileum and transverse colon) were cocultured for 8 hours with E. coli O42, Lactobacillus GG (LGG), Bacteroidesthetaiotaomicron (B. theta), or stimulated with interleukin (IL)-1β (positive control). Matched nonstimulated biopsies served as experimental controls. IL-8 was the immune marker of choice. IL-8 mRNA and protein levels were quantified by quantitative polymerase chain reaction and sandwich enzyme-linked immunosorbent assay, respectively.

RESULTS

IL-8 secretion was observed when control, ileal biopsies were exposed to pathogenic O42 and probiotic LGG, with no response noted to commensal B. theta. In comparison, Crohn's ileal biopsies showed impaired ability to induce IL-8 in response to O42 and LGG. Control colonic tissue showed a limited response to O42 or B. theta and LGG significantly reduced IL-8 secretion. Unlike control tissue, however, Crohn's ileal and colonic tissue did respond to B. theta, with more enhanced expression in the colon.

CONCLUSIONS

We provide the first ex vivo data to support the notion that aberrant mucosal recognition of commensal bacteria may contribute to pediatric CD. While IL-8 responses to O42 and LGG varied with disease status and anatomical location, B. theta consistently induced significant IL-8 both in ileal and colonic CD tissue, which was not seen in control, healthy tissue.

Escherichia coli enteroagregativa como agente provocador de diarreia persistente: modelo experimental utilizando microscopia óptica de luz

OBJETIVO: Avaliar interações de amostras de Escherichia coli enteroagregativa com tecido intestinal humano, a fim de documentar potenciais alterações em diferentes regiões do trato digestivo. MÉTODOS: Amostras de Escherichia coli enteroagregativa isoladas das fezes de crianças com diarreia persistente e a amostra protótipo 042, isolada de uma criança com diarreia em Lima, no Peru (controle positivo), foram analisadas por microscopia óptica de luz após semeadura em cultura de orgão in vitro de fragmentos de mucosa ileal e colônica. Foram analisadas as interações entre as diferentes cepas de Escherichia coli enteroagregativa e as mucosas ileal e colônica. RESULTADOS: A análise por microscopia óptica de luz indicou associação destes micro-organismos com o epitélio, provocando alterações. As cepas estudadas aderiram a ambas as regiões avaliadas (intestino delgado distal e grosso) e causaram alterações, especialmente naquelas áreas onde interagiram diretamente com o epitélio. No íleo, algumas regiões mostraram internalização secundária. CONCLUSÕES: Esses agentes podem causar diarreia persistente por meio de alterações no intestino delgado, no qual ocorrem as funções digestivo-absortivas. As lesões inflamatórias descritas na mucosa colônica poderiam explicar a colite mostrada em algumas crianças infectadas por Escherichia coli enteroagregativa.

Characterization of genes associated with internalization of enteroaggregative Escherichia coli

On animal models enteroaggregative Escherichia coli (EAEC) can cause mild, but significant mucosal damage, suggesting the invasive capability of these strains. In the study we investigated the ability of typical, aggR-positive and atypical, aggR-negative EAEC isolates to enter intestinal epithelial Int407 cells in relation to the distribution of genes encoding the putative invasins described among pathogenic E. coli categories. The results demonstrated that regardless of origin and affiliation to typical and atypical EAEC, most isolates examined were internalized by the epithelial cells to different extent. Although as many as 50 (84.3%) EAEC demonstrated a variety of combinations of the aggB, afaD, ipaH and tia genes determined, there was no correlation between the invasion efficiency of these strains and the presence of any particular gene involved in invasion. Most of EAEC examined belonged to phylogenetic group B2 and D.

Delineation of the innate and adaptive T-cell immune outcome in the human host in response to Campylobacter jejuni infection

BACKGROUND

Campylobacter jejuni is the most prevalent cause of bacterial gastroenteritis worldwide. Despite the significant health burden this infection presents, molecular understanding of C. jejuni-mediated disease pathogenesis remains poorly defined. Here, we report the characterisation of the early, innate immune response to C. jejuni using an ex-vivo human gut model of infection. Secondly, impact of bacterial-driven dendritic cell activation on T-cell mediated immunity was also sought.

METHODOLOGY

Healthy, control paediatric terminal ileum or colonic biopsy tissue was infected with C. jejuni for 8-12 hours. Bacterial colonisation was followed by confocal microscopy and mucosal innate immune responses measured by ELISA. Marked induction of IFNγ with modest increase in IL-22 and IL-17A was noted. Increased mucosal IL-12, IL-23, IL-1β and IL-6 were indicative of a cytokine milieu that may modulate subsequent T-cell mediated immunity. C. jejuni-driven human monocyte-derived dendritic cell activation was followed by analyses of T cell immune responses utilising flow cytometry and ELISA. Significant increase in Th-17, Th-1 and Th-17/Th-1 double-positive cells and corresponding cytokines was observed. The ability of IFNγ, IL-22 and IL-17 cytokines to exert host defence via modulation of C. jejuni adhesion and invasion to intestinal epithelia was measured by standard gentamicin protection assay.

CONCLUSIONS

Both innate and adaptive T cell-immunity to C. jejuni infection led to the release of IFNγ, IL-22 and IL-17A; suggesting a critical role for this cytokine triad in establishing host anti-microbial immunity during the acute and effectors phase of infection. In addition, to their known anti-microbial functions; IL-17A and IL-17F reduced the number of intracellular C. jejuni in intestinal epithelia, highlighting a novel aspect of how IL-17 family members may contribute to protective immunity against C. jejuni.

Enteroaggregative Escherichia coli plasmid-encoded toxin

Plasmid-encoded toxin (Pet) is secreted by enteroaggregative Escherichia coli (EAEC), a pathotype of diarrhogenic E. coli. EAEC infection is an important cause of diarrhea in outbreak and nonoutbreak settings in developing and developed countries. EAEC secretes Pet by using the type V secretion system. Mature secreted Pet is a serine protease and its eukaryotic target is the actin-binding protein alpha-fodrin. When Pet cleaves alpha-fodrin in the target cell cytosol, the organization of the actin cytoskeleton is disrupted. The loss of actin filament structure results in cell rounding and detachment from the substratum. This article summarizes the long trip of Pet during its biogenesis, its interaction with epithelial cells, intracellular trafficking and mechanism of action.

Ingested Shiga toxin 2 (Stx2) causes histopathological changes in kidney, spleen, and thymus tissues and mortality in mice

The Shiga toxin (Stx)-producing bacterial strain, Escherichia coli O157:H7, colonizes the distal small intestine and the colon, initiating serious illness, including hemolytic-uremic syndrome (HUS), characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. Although intravenous administration of purified Stx to primates has been able to reproduce the features of HUS, it has not been conclusively established as to whether ingestion of Stx alone without the bacterium poses a potential health risk. To help answer this question, in this study, we fed Shiga toxin 2 (Stx2) directly into the stomachs of mice via gavage. Our data show that ingestion of Stx2 at a concentration of 50 μg/mouse induces weight loss and kills the mice at 3-5 days post-gavage. Additional studies revealed that the toxin retains activity at low pH, that its activity is neutralized by treatment with toxin-specific antibody, and that about 1% of the fed toxin is absorbed into the blood circulation. Lethality by intraperitoneal (IP) injection of Stx2 occurred at much lower doses than by ingestion. Detailed histopathological evaluation of stained tissues by light microscopy revealed severe histopathological changes in kidneys, spleen, and thymus but not in the pancreas, lymph nodes, heart, lungs, trachea, esophagus, stomach, duodenum, jejunum, ileum, cecum, and colon. The pathological changes in the kidney appeared similar to those seen in humans with HUS. The cited data suggest that (a) most but not all of the toxin is inactivated in the digestive tract, (b) part of the oral-ingested toxin is absorbed from the digestive tract into the circulation, (c) enough active toxin reaches susceptible organs to induce damage, and (d) Stx2 in the absence of toxin-producing bacteria can be harmful to mice. The results are clinically relevant for food safety because we also found that heat treatments (pasteurization) that destroy bacteria did not inactivate the heat-resistant toxin produced and secreted by the bacteria.

Pic, an autotransporter protein secreted by different pathogens in the Enterobacteriaceae family, is a potent mucus secretagogue

A hallmark of enteroaggregative Escherichia coli (EAEC) infection is a formation of biofilm, which comprises a mucus layer with immersed bacteria in the intestines of patients. While studying the mucinolytic activity of Pic in an in vivo system, rat ileal loops, we surprisingly found that EAEC induced hypersecretion of mucus, which was accompanied by an increase in the number of mucus-containing goblet cells. Interestingly, an isogenic pic mutant (EAEC Δpic) was unable to cause this mucus hypersecretion. Furthermore, purified Pic was also able to induce intestinal mucus hypersecretion, and this effect was abolished when Pic was heat denatured. Site-directed mutagenesis of the serine protease catalytic residue of Pic showed that, unlike the mucinolytic activity, secretagogue activity did not depend on this catalytic serine protease motif. Other pathogens harboring the pic gene, such as Shigella flexneri and uropathogenic E. coli (UPEC), also showed results similar to those for EAEC, and construction of isogenic pic mutants of S. flexneri and UPEC confirmed this secretagogue activity. Thus, Pic mucinase is responsible for one of the pathophysiologic features of the diarrhea mediated by EAEC and the mucoid diarrhea induced by S. flexneri.

A pathoadaptive deletion in an enteroaggregative Escherichia coli outbreak strain enhances virulence in a Caenorhabditis elegans model

Enteroaggregative Escherichia coli (EAEC) strains are important diarrheal pathogens. EAEC strains are defined by their characteristic stacked-brick pattern of adherence to epithelial cells but show heterogeneous virulence and have different combinations of adhesin and toxin genes. Pathoadaptive deletions in the lysine decarboxylase (cad) genes have been noted among hypervirulent E. coli subtypes of Shigella and enterohemorrhagic E. coli. To test the hypothesis that cad deletions might account for heterogeneity in EAEC virulence, we developed a Caenorhabditis elegans pathogenesis model. Well-characterized EAEC strains were shown to colonize and kill C. elegans, and differences in virulence could be measured quantitatively. Of 49 EAEC strains screened for lysine decarboxylase activity, 3 tested negative. Most notable is isolate 101-1, which was recovered in Japan, from the largest documented EAEC outbreak. EAEC strain 101-1 was unable to decarboxylate lysine in vitro due to deletions in cadA and cadC, which, respectively, encode lysine decarboxylase and a transcriptional activator of the cadAB genes. Strain 101-1 was significantly more lethal to C. elegans than control strain OP50. Lethality was attenuated when the lysine decarboxylase defect was complemented from a multicopy plasmid and in single copy. In addition, restoring lysine decarboxylase function produced derivatives of 101-1 deficient in aggregative adherence to cultured human epithelial cells. Lysine decarboxylase inactivation is pathoadapative in an important EAEC outbreak strain, and deletion of cad genes could produce hypervirulent EAEC lineages in the future. These results suggest that loss, as well as gain, of genetic material can account for heterogeneous virulence among EAEC strains.

Host-Toxin Interactions Involving EspC and Pet, Two Serine Protease Autotransporters of the Enterobacteriaceae

EspC and Pet are toxins secreted by the diarrheagenic enteropathogenic and enteroaggregative Escherichia coli pathotypes, respectively. Both toxins have a molecular mass around 110 kDa and belong to the same protein family called Serine Protease Autotransporters of the Enterobacteriaceae (SPATE). Furthermore, both toxins act within the cytosol of intoxicated epithelial cells to disrupt the architecture of the actin cytoskeleton. This cytopathic and enterotoxic effect results from toxin cleavage of the actin-binding protein fodrin, although the two toxins recognize different cleavage sites on fodrin. EspC and Pet also have dramatically different mechanisms of entering the target cell which appear dependent upon the E. coli pathotype. In this review, we compare/contrast EspC and Pet in regards to their mode of delivery into the target cell, their effects on fodrin and the actin cytoskeleton, and their possible effects on the physiology of the intestinal epithelial cell.

Galactose specific adhesin of enteroaggregative E. coli induces IL-8 secretion via activation of MAPK and STAT-3 in INT-407 cells

BACKGROUND

Enteroaggregative Escherichia coli (EAEC) is one of the most common bacterial pathogens associated with the etiology of persistent diarrhea. A characteristic feature of EAEC-pathogenesis is the induction of profound inflammatory response in the intestinal epithelium. The present study was designed to investigate the underlying mechanism of inflammatory responses induced by a novel galactose specific adhesin of T7 strain of EAEC (EAEC-T7) in human intestinal epithelial cell line (INT-407).

METHODS

INT-407 cells were stimulated with the adhesin in the absence and presence of anti-adhesin (IgG(AD))/d-galactose/H7/staurosporin (inhibitor of PKC)/PD098059 (inhibitor of MEK)/SB203580 (inhibitor of p38-MAPkinase)/AG490 (inhibitor of JAK (-2,-3)/STAT-3 pathway). The expression of activated Raf-1, MEK-1, ERK1/2, JNK, p38-MAPK and STAT-3 was analyzed by Western immunoblot. Release of interleukin-8 (IL-8) was measured by ELISA.

RESULTS

The adhesin was found to induce activation of Raf-1, MEK-1, ERK1/2, p38-MAPK and STAT-3, which was reduced in the presence of IgG(AD)/d-galactose. The activation of Raf-1 was found to be attenuated in the presence of H7/staurosporin. The expression of phosphorylated STAT-3 was downregulated in the presence of AG490 and PD098059. Further, the adhesin induced IL-8 secretion was reduced in the presence of the inhibitors of MEK (PD098059), p38-MAPK (SB203580) and JAK (-2,-3)/STAT-3 pathway (AG490).

CONCLUSIONS

We propose that STAT-3 activation is quintessential for the galactose specific adhesin induced IL-8 secretion by INT-407 cells and must occur in concert with the activation of ERK1/2.

GENERAL SIGNIFICANCE

Our contribution regarding the galactose specific adhesin mediated signaling leads to an improved understanding of the EAEC-pathogenesis and may provide novel therapeutic approaches to combat EAEC infection.

Enteroaggregative Escherichia coli: An Emerging Enteric Food Borne Pathogen

Enteroaggregative Escherichia coli (EAEC) are quite heterogeneous category of an emerging enteric pathogen associated with cases of acute or persistent diarrhea worldwide in children and adults, and over the past decade has received increasing attention as a cause of watery diarrhea, which is often persistent. EAEC infection is an important cause of diarrhea in outbreak and non-outbreak settings in developing and developed countries. Recently, EAEC has been implicated in the development of irritable bowel syndrome, but this remains to be confirmed. EAEC is defined as a diarrheal pathogen based on its characteristic aggregative adherence (AA) to HEp-2 cells in culture and its biofilm formation on the intestinal mucosa with a “stacked-brick” adherence phenotype, which is related to the presence of a 60 MDa plasmid (pAA). At the molecular level, strains demonstrating the aggregative phenotype are quite heterogeneous; several virulence factors are detected by polymerase chain reaction; however, none exhibited 100% specificity. Although several studies have identified specific virulence factor(s) unique to EAEC, the mechanism by which EAEC exerts its pathogenesis is, thus, far unknown. The present review updates the current knowledge on the epidemiology, chronic complications, detection, virulence factors, and treatment of EAEC, an emerging enteric food borne pathogen.

Enteroaggregative Escherichia coli infection induces IL-8 production via activation of mitogen-activated protein kinases and the transcription factors NF-kappaB and AP-1 in INT-407 cells

Enteroaggregative Escherichia coli (EAEC) is emerging as a cause of acute and persistent diarrhea in developing countries. An important feature of EAEC pathogenesis is the induction of profound inflammatory response in the intestinal epithelium. In this article, we have shown that EAEC-induced activation of mitogen-activated protein kinases (MAPK) (ERK-1/2, JNK and p38MAPK) in cultured human intestinal epithelial cells (INT-407) leads to the induction of DNA-binding activity of NF-kappaB and AP-1, resulting in IL-8 production. Plasmid-cured EAEC could also activate the MAPK and the transcription factors leading to IL-8 secretion, but to a lesser extent than that of wild-type EAEC. Further, pretreatment of these cells with the highly specific MEK inhibitor (PD 098059), the JNK inhibitor (SP 600125), and the p38MAPK inhibitor (SB 203580) resulted in inhibition of the IL-8 secretion by EAEC (wild type as well as plasmid cured)-infected INT-407 cells. These findings demonstrate that the inflammatory response induced by EAEC may be due to the specific stimulation of MAPK signaling pathways leading to nuclear responses. To our knowledge, this is the first article regarding the detailed mechanism of IL-8 secretion from the EAEC-infected human intestinal epithelial cell line.

Cellular response induced by a galactose-specific adhesin of enteroaggregative Escherichia coli in INT-407 cells

In the present study, the role of a fimbrial galactose-specific adhesin of the T7 strain of enteroaggregative Escherichia coli (EAEC-T7) in the signal transduction pathways in human small intestinal epithelial cells (INT-407) was explored. The adhesin was purified by anion exchange chromatography using a Mono Q HR5/5 column in the AKTA purifier system. The characteristic stacked brick pattern of aggregative adherence of EAEC-T7 to INT-407 cells was found to be inhibited in the presence of immunoglobulin G against the purified adhesin as well as d-galactose. The adhesin induced a significant increase in the intracellular calcium concentration [Ca(2+)](i) in INT-407 cells, which was reduced in the presence of dantrolene (inhibitor of intracellular calcium stores), verapamil, calciseptin (calcium channel blockers) as well as neomycin [inhibitor of phospholipase C (PLC)]. Further, an increased level of PLCgamma1 and inositol 1,4,5-tri phosphate as well as enhanced activity of protein kinase C (PKC) in the adhesin-stimulated cells were found to be downregulated in the presence of neomycin and U73122 (inhibitors of PLC) and H-7 (inhibitor of PKC), respectively. The adhesin could also induce interleukin-8 secretion from INT-407 cells, which was inhibited in the presence of dantrolene as well as staurosporin (inhibitor of PKC). Collectively, our results have suggested that the galactose-specific adhesin-induced signal transduction pathway might play a crucial role in the EAEC-induced pathogenesis.

The ex vivo response of human intestinal mucosa to enteropathogenic Escherichia coli infection

In vitro organ culture (IVOC) represents a gold standard model to study enteropathogenic E. coli (EPEC) infection of human intestinal mucosa. However, the optimal examination of the bacterial-host cell interaction requires a directional epithelial exposure, without serosal or cut surface stimulation. A polarized IVOC system (pIVOC) was developed in order to overcome such limitations: apical EPEC infection produced negligible bacterial leakage via biopsy edges, resulted in enhanced colonization compared with standard IVOC, and showed evidence of bacterial detachment, as in natural rabbit EPEC infections. Examination of mucosal innate immune responses in pIVOC showed both interleukin (IL)-8 mRNA and protein levels were significantly increased after apical EPEC infection. Increased IL-8 levels mainly depended on flagellin expression as fliC-negative EPEC did not elicit a significant IL-8 response despite increased mucosal colonization compared with wild-type EPEC. In addition, apical application of purified flagella significantly increased IL-8 protein levels over non-infected controls. Immunofluorescence staining of EPEC-infected small intestinal biopsies revealed apical and basolateral distribution of Toll-like receptor (TLR) 5 on epithelium, suggesting that EPEC can trigger mucosal IL-8 responses by apical flagellin/TLR5 interaction ex vivo and does not require access to the basolateral membrane as postulated in cell culture models.

Enteroaggregative Escherichia coli (EAEC) strains enter and survive within cultured intestinal epithelial cells

Enteroaggregative Escherichia coli (EAEC) is an emerging pathogen associated to cases of acute or persistent diarrhea in children and adults from developed and developing countries. These microorganisms also have been isolated from human immunodeficiency virus-infected patients. EAEC exhibits aggregative adherence (AA) in HEp-2 cells. This pattern is characterized by the production of bacteria aggregates adhered to monolayer cultured cells with a "stacked brick" phenotype. The AA pattern is related to the presence of a 60MDa plasmid (pAA). In the present study, we evaluated the adherence, invasion and persistent survival of five EAEC strains with Caco-2 and T84 cells, by a bacteria invasion assay and transmission electron microscopy. EAEC isolated from cases of acute infantile diarrhea can be internalized by intestinal epithelial cells cultivated in vitro, suggesting that these strains may employ a mechanism of host cell invasion to colonize the intestinal mucosa. Results showed that EAEC strains could survive intracellularly up to 72h. Our data support evidence that EAEC is able to invade, persist and replicate within intestinal cells for extended time. This strategy may be advantageous to EAEC in colonization and survival, favoring the exploitation of an intracellular niche where these strains are protected against host clearance mechanisms, immune system and antibiotic treatment. Intracellular persistence of EAEC may be associated with development of persistent diarrhea associated to these microorganisms. To our knowledge, this is the first report of EAEC intracellular survival in cultured intestinal epithelial cells.

Structural studies of the O-antigenic polysaccharides from the enteroaggregative Escherichia coli strain 87/D2 and international type strains from E. coli O128

The O-antigen of the lipopolysaccharide (LPS) from the enteroaggregative Escherichia coli strain 87/D2 has been determined by component analysis together with NMR spectroscopy. The polysaccharide has pentasaccharide repeating units in which all the residues have the galacto-configuration. The repeating unit of the O-antigen, elucidated using the O-deacylated LPS, is branched with the following structure: Analysis of the 1H NMR spectrum of the LPS revealed O-acetyl groups (approximately 0.7 per repeating unit) distributed over two positions. Subsequent analysis showed that the galactose residue carries acetyl groups at either O-3 or O-4 in a ratio of approximately 2:1. The international reference strain from E. coli O128ab was investigated and the repeating unit of the O-antigens has the following structure: Analysis of the 1H NMR spectrum of the LPS revealed O-acetyl groups (approximately one per repeating unit) distributed over two positions. The integrals of the resonances for the O-acetyl groups indicated similarities between the O-antigen from E. coli O128ab and that of E. coli strain 87/D2, whereas the O-acetyl substitution pattern in the E. coli O128ac O-antigen differed slightly. Enzyme immunoassay using specific anti-E. coli O128ab and anti-E. coli O128ac rabbit sera confirmed the results.

Human intestinal tissue tropism in Escherichia coli O157 : H7--initial colonization of terminal ileum and Peyer's patches and minimal colonic adhesion ex vivo

Enterohaemorrhagic Escherichia coli (EHEC) are an important cause of diarrhoeal and renal disease in man. Studies of a single prototypic O157 : H7 strain have shown tropism for follicle-associated epithelium (FAE) of distal ileal Peyer's patches without colonization of either small or large intestine. This study determined tropism in a range of Shiga toxin (Stx)-negative EHEC strains and looked for factors that might induce colonic colonization using human in vitro intestinal organ culture (IVOC). An FAE-restricted colonization was confirmed in two strains; four strains additionally colonized ileal villous surfaces, and adhesion to proximal small intestinal FAE was observed. All strains showed minimal adhesion to non-FAE regions of proximal small intestinal and to the transverse colon. Extensive large-bowel IVOC studies using three O157 : H7 strains, an O26 : H11 and an O103 : H2 strain, and tissue from caecum to rectum found colonization and attaching/effacing lesion formation in only 4 of 113 (3.5 %) IVOCs. Colonic adhesion was not enhanced by altering the IVOC technique or environment. Co-incubation of O157 : H7-infected ileal FAE with colonic samples enhanced colonic colonization, producing a novel, non-intimate adhesive phenotype. Thus, in the initial stages of colonization Stx-negative EHEC preferentially infect FAE and villi of the terminal ileal region ex vivo; colonic colonization is infrequently observed as an initial event but may represent a subsequent stage of infection.

Enteroaggregative Escherichia coli: epidemiology, virulence and detection

Enteroaggregative Escherichia coli (EAEC) is a subgroup of diarrhoeagenic E. coli (DEC) that during the past decade has received increasing attention as a cause of watery diarrhoea, which is often persistent. EAEC have been isolated from children and adults worldwide. As well as sporadic cases, outbreaks of EAEC-caused diarrhoea have been described. The definition of EAEC is the ability of the micro-organism to adhere to epithelial cells such as HEp-2 in a very characteristic ‘stacked-brick’ pattern. Although many studies searching for specific virulence factor(s) unique for this category of DEC have been published it is still unknown why the EAEC cause persistent diarrhoea. In addition, the aggregative property of EAEC causes a lot of problems in serotyping due to the cells auto-agglutinating. The gold standard for identification of EAEC includes isolation of the agent and an adherence assay using tissue culture, viz. HEp-2 cells. This assay is in most cases reliable; however, emergence of ‘atypical’ EAEC has been described in several publications. In addition, the HEp-2 assay is time consuming, demands a tissue culture lab and trained staff. Several molecular biological assays have been described, however, none show 100 % specificity.

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

Escherichia coli O26 is recognized as an emerging pathogen associated with disease in both ruminants and humans. Compared to those of E. coli O157:H7, the shedding pattern and location of E. coli O26 in the gastrointestinal tract (GIT) of ruminants are poorly understood. In the studies reported here, an stx-negative E. coli O26 strain of ovine origin was inoculated orally into 6-week-old lambs and the shedding pattern of the O26 strain was monitored by serial bacteriological examination of feces. The location of colonization in the GIT was examined at necropsy at two time points. The numbers of O26 organisms excreted in feces declined from approximately 10(7) to 10(4) CFU per gram of feces by day 7 and continued at this level for a further 3 weeks. Beyond day 30, excretion was from few animals, intermittent, and just above the detection limit. By day 38, all fecal samples were negative, but at necropsy, O26 organisms were recovered from the upper GIT, specifically the ileum. However, no attaching-effacing (AE) lesions were observed. To identify the location of E. coli O26 within the GIT early after inoculation, two lambs were examined postmortem, 4 days postinoculation. High numbers of O26 organisms were recovered from all GIT sites examined, and approximately 10(9) CFU were recovered from 1 gram of ileal tissue from one animal. Despite high numbers of O26 organisms, AE lesions were identified on the mucosa of the ascending colon of only one animal. These data indicate that E. coli O26 readily colonizes 6-week-old lambs, but the sparseness of AE lesions suggests that O26 is well adapted to this host, and mechanisms other than those dependent upon intimin may play a role in persistence.

Proteomic and microarray characterization of the AggR regulon identifies a pheU pathogenicity island in enteroaggregative Escherichia coli

Enteroaggregative Escherichia coli (EAEC) is defined by aggregative adherence (AA) to HEp-2 cells, where bacteria display adherence to cell surfaces and also to the intervening substratum in a stacked-brick configuration. We previously showed that an AraC homologue designated AggR is required for the expression of plasmid-encoded genes that mediate AA of EAEC strain 042. In this study, we hypothesized that AggR also controls the expression of other virulence determinants in EAEC 042. Using proteomic and microarray analysis, we identified for the first time that AggR activates the expression of chromosomal genes, including 25 contiguous genes (aaiA-Y), which are localized to a 117 kb pathogenicity island (PAI) inserted at pheU. Many of these genes have homologues in other Gram-negative bacteria and were recently proposed to constitute a type VI secretion system (T6SS). AaiC was identified as a secreted protein that has no apparent homologues within GenBank. EAEC strains carrying in-frame deletions of aaiB, aaiG, aaiO or aaiP still synthesized AaiC; however, AaiC secretion was abolished. Cloning of aai genes into E. coli HB101 suggested that aaiA-P are sufficient for AaiC secretion. A second T6SS was identified within the pheU PAI that secretes a protein unrelated by sequence identity to AaiC. Distribution studies indicated that aaiA and aaiC are commonly found in EAEC isolates worldwide, particularly in strains defined as typical EAEC. These data support the hypothesis that AggR is a global regulator of EAEC virulence determinants, and builds on the hypothesis that T6SS is an importance mediator of pathogenesis.

Association of putative enteroaggregative Escherichia coli virulence genes and biofilm production in isolates from travelers to developing countries

Enteroaggregative Escherichia coli (EAEC) is an emerging enteric pathogen that causes acute and chronic diarrhea among children, human immunodeficiency virus-infected patients, and travelers to developing regions of the world. The pathogenesis of EAEC strains involves the production of biofilm. In this study, we determined the association between presence of putative EAEC virulence genes and biofilm formation in 57 EAEC isolates (as defined by HEp-2 adherence) from travelers with diarrhea and in 18 EAEC isolates from travelers without diarrhea. Twelve nondiarrheagenic E. coli isolates from healthy travelers were used as controls. Biofilm formation was measured by using a microtiter plate assay with the crystal violet staining method, and the presence of the putative EAEC virulence genes aap, aatA, aggR, astA, irp2, pet, set1A, and shf was determined by PCR. EAEC isolates were more likely to produce biofilm than nondiarrheagenic E. coli isolates (P = 0.027), and the production of biofilm was associated with the virulence genes aggR, set1A, aatA, and irp2, which were found in 16 (40%), 17 (43%), 10 (25%), and 27 (68%) of the biofilm producers versus only 4 (11%), 6 (6%), 2 (6%), and 15 (43%) in non-biofilm producers (P = 0.008 for aggR, P = 0.0004 for set1A, P = 0.029 for aatA, and P = 0.04 for irp2). Although the proportion of EAEC isolates producing biofilm in patients with diarrhea (51%) was similar to that in patients without diarrhea (61%), biofilm production was related to the carriage of aggR (P = 0.015), set1A (P = 0.001), and aatA (P = 0.025). Since aggR is a master regulator of EAEC, the presence of aap (P = 0.004), astA (P = 0.001), irp2 (P = 0.0006), pet (P = 0.002), and set1A (P = 0.014) in an aggR versus an aggR-lacking background was investigated and was also found to be associated with biofilm production. This study suggests that biofilm formation is a common phenomenon among EAEC isolates derived from travelers with or without diarrhea and that multiple genes associated with biofilm formation are regulated by aggR.

Development of anex vivoorgan culture model using human gastro-intestinal tissue andCampylobacter jejuni

Campylobacter jejuni is an important food-borne pathogen. However, relatively little is understood regarding its pathogenesis, and research is hampered by the lack of a suitable model. Recently, a number of groups have developed assays to study the pathogenic mechanisms of C. jejuni using cell culture models. Here, we report the development of an ex vivo organ culture model, allowing for the maintenance of intestinal mucosal tissue, to permit more complex host-bacterium interactions to be studied. Ex vivo organ culture highlights the propensity for C. jejuni to adhere to mucosal tissue via the flagellum, either as discrete colonies or as multicellular units.

A review of an emerging enteric pathogen: enteroaggregative Escherichia coli

Enteroaggregative Escherichia coli (EAEC) is an increasingly recognized enteric pathogen. It is a cause of both acute and persistent diarrhoea among children, adults and HIV-infected persons, in both developing and developed countries. In challenge studies, EAEC has caused diarrhoeal illness with the ingestion of 1010 c.f.u. Outbreaks of diarrhoeal illness due to EAEC have been reported, and linked to the ingestion of contaminated food. Diarrhoeal illness due to EAEC is the result of a complex pathogen–host interaction. Some infections due to EAEC result in diarrhoeal illness and elicit an inflammatory response, whereas other infections do not result in a symptomatic infection. Many putative virulence genes and EAEC strains that produce biofilm have been identified; however, the clinical significance of these genes and of biofilm production has yet to be defined. A −251 AA single nucleotide polymorphism (SNP) in the interleukin (IL)-8 promoter region is reported to increase host susceptibility to EAEC diarrhoea. Ciprofloxacin and rifaximin continue to be an effective treatment in persons infected with EAEC. This review is intended to provide an updated review for healthcare workers on EAEC, an emerging enteric pathogen.

Prevention and self-treatment of traveler's diarrhea

Of the millions who travel from the industrialized world to developing countries every year, between 20% and 50% will develop at least one episode of diarrhea, making it the most common medical ailment afflicting travelers. Although usually a mild illness, traveler's diarrhea can result in significant morbidity and hardship overseas. Precautions can be taken to minimize the risk of developing traveler's diarrhea, either through avoidance of potentially contaminated food or drink or through various prophylactic measures, including both nonpharmacological and antimicrobial strategies. If diarrhea does develop despite the precautions taken, effective treatment-usually a combination of an antibiotic and an antimotility agent-can be brought by the traveler and initiated as soon as symptoms develop. In the future, vaccines-several of which are in the advanced stages of clinical testing-may be added to the list of prophylactic measures.

The structures ofEscherichia coliO-polysaccharide antigens

Escherichia coli is usually a non-pathogenic member of the human colonic flora. However, certain strains have acquired virulence factors and may cause a variety of infections in humans and in animals. There are three clinical syndromes caused by E. coli: (i) sepsis/meningitis; (ii) urinary tract infection and (iii) diarrhoea. Furthermore the E. coli causing diarrhoea is divided into different 'pathotypes' depending on the type of disease, i.e. (i) enterotoxigenic; (ii) enteropathogenic; (iii) enteroinvasive; (iv) enterohaemorrhagic; (v) enteroaggregative and (vi) diffusely adherent. The serotyping of E. coli based on the somatic (O), flagellar (H) and capsular polysaccharide antigens (K) is used in epidemiology. The different antigens may be unique for a particular serogroup or antigenic determinants may be shared, resulting in cross-reactions with other serogroups of E. coli or even with other members of the family Enterobacteriacea. To establish the uniqueness of a particular serogroup or to identify the presence of common epitopes, a database of the structures of O-antigenic polysaccharides has been created. The E. coli database (ECODAB) contains structures, nuclear magnetic resonance chemical shifts and to some extent cross-reactivity relationships. All fields are searchable. A ranking is produced based on similarity, which facilitates rapid identification of strains that are difficult to serotype (if known) based on classical agglutinating methods. In addition, results pertinent to the biosynthesis of the repeating units of O-antigens are discussed. The ECODAB is accessible to the scientific community at http://www.casper.organ.su.se/ECODAB/.

Pathogenesis of enteroaggregative Escherichia coli infection

Enteroaggregative Escherichia coli (EAEC) is emerging as a significant diarrheal pathogen in multiple population groups. Although most commonly associated with pediatric diarrhea in developing countries, EAEC is also linked to diarrhea in adults including HIV-positive patients and travelers and has been a cause of food-borne outbreaks in the industrialized world. Current data suggest that one set of virulence elements is not associated with all EAEC strains, but that combinations of multiple factors prevail. Pathogenesis is believed to be initiated with adherence to the terminal ileum and colon in an aggregative, stacked-brick-type pattern by means of one of several different hydrophobic aggregative adherence fimbriae. Some strains of EAEC may then elaborate cytotoxins including the plasmid-encoded toxin and the enterotoxins, EAST1 and ShET1. An AraC homolog termed AggR regulates several genes contributing to fimbrial biogenesis in 'typical EAEC strains'. AggR has now also been shown to regulate genes on a chromosomal island. Sequencing of the EAEC type strain 042 completed at the Sanger Center has revealed two other chromosomal islands that are being explored for their pathogenetic potential. This article reviews these virulence elements and presents on-going areas of research in EAEC pathogenesis.

A comparison of Shiga-toxin negative Escherichia coli O157 aflagellate and intimin deficient mutants in porcine in vitro and in vivo models of infection

Isolation of Shiga-toxin (Stx) positive Escherichia coli O157:H7 from commercially grown pigs has been reported. Furthermore, experimental infection studies have demonstrated that Stx-positive E. coli O157:H7 can persist in 12-week-old experimentally orally inoculated conventional pigs for up to 2 months and that persistence was not dependent upon intimin. We have shown that the flagellum of Stx-negative E. coli O157:H7 does not have a role to play in pathogenesis in ruminant models whereas, in poultry, the flagellum of E. coli O157:H7 was important for long-term persistent infection. The contribution of the flagellum of Stx-negative E. coli O157 in the colonisation of pigs was investigated by adherence assays on a porcine (IPI-21) cell line, porcine in vitro organ culture (IVOC) and experimental oral inoculation of conventional 14-week-old pigs. E. coli O157:H7 NCTC12900nal(r) and isogenic aflagellate and intimin deficient mutants adhered equally well to IPI-21 cells. In porcine IVOC association assays, E. coli O157:H7 NCTC12900nal(r) was associated in significantly higher numbers to tissues from the caecum and the terminal rectum than other sites. The aflagellate and intimin deficient mutants significantly adhered in greater numbers to more IVOC gastrointestinal tissues than the parent. Groups of 14-week-old pigs were dosed orally with 10(10)CFU/10ml of either E. coli O157:H7 NCTC12900nal(r) or isogenic aflagellate and intimin deficient mutants and recovery of each test strain was similar. Histological analysis of pig tissues at post mortem examination revealed that E. coli O157 specifically stained bacteria were associated with the mucosa of the ascending and spiral colon. These data suggest that colonisation and persistence of Stx-negative E. coli O157:H7 in pigs, involves mechanisms that do not require the flagellum or intimin.

Attachment of Mycobacterium avium subspecies paratuberculosis to bovine intestinal organ cultures: Method development and strain differences

Mycobacterium avium spp. paratuberculosis (MAP) causes chronic granulomatous inflammation of the intestinal tract in many species of animals, but the mechanisms of disease are poorly understood. Attachment of bacteria to epithelial cells is a critical step in pathogenesis of many mucosal diseases. The goal of these studies was to develop an in vitro method to study attachment of MAP to bovine intestinal epithelial cells. Short-term, bovine intestinal organ cultures were used to show a significant difference in the ability of radiolabelled MAP strains to attach to intestinal epithelium. We found significant differences in the ability of different strains of MAP to attach, but there were no differences in attachment among different regions of the intestinal tract. Examination of acid fast stained tissue sections of organ cultures demonstrated that organisms were located adjacent to mucosal epithelium or within goblet cells. Coating of the organisms with fibronectin, which has been shown to be involved in attachment of many mycobacteria, including MAP, affected the attachment of the MAP strains in different ways, but did not affect the overall attachment of the organisms to different regions of the gastrointestinal tract. This organ culture method should also prove useful for defining the molecular mechanisms of attachment and interactions of MAP with intestinal epithelium.

Enteroaggregative Escherichia coli: An emerging pathogen in children

Enteroaggregative Escherichia coli (EAEC) is an emerging pathogen that causes enteric and food-borne infectious diseases. Children throughout the world appear to be susceptible to EAEC infection. EAEC pathogenesis involves the following three stages: 1) adherence to the intestinal mucosa; 2) increased production and deposition of a mucus biofilm; and 3) mucosal toxicity due to inflammation and cytokine release. The HEp-2 cell adherent assay allows identification of EAECs characteristic aggregative or "stacked brick" adherence pattern. Antimicrobial treatment of children who develop an EAEC infection should be individually based. All children with EAEC diarrhea should receive adequate oral fluid hydration. For children who have persistent diarrhea and severe dehydrating illness despite having received adequate oral rehydration, antimicrobials may be initiated. Azithromycin and rifaximin have been shown to shorten the course of EAEC diarrhea in adults and probably represent the recommended antimicrobials of choice for children with severe or persistent illness. The objective of this review is to increase awareness of this important emerging pathogen and to discuss the epidemiology, pathogenesis, and pathogen and host factors associated with EAEC infection in children.

Use of a continuous-flow anaerobic culture to characterize enteric virulence gene expression

We developed an in vitro culture method to characterize the expression of bacterial genes under conditions mimicking the colonic environment. Our culture system (the intestinal simulator) comprised a continuous-flow anaerobic culture which was inoculated with fecal samples from healthy volunteers. As a test organism, we employed enteroaggregative Escherichia coli (EAEC), an emerging diarrheal pathogen that is thought to cause infection in both the small and large intestines. After the simulator culture achieved equilibrium conditions, we inoculated the system with prototype EAEC strain 042 and assessed the expression of three EAEC virulence-related genes. We focused particularly on expression of aggR, which encodes a global transcriptional regulator of EAEC virulence factors, and two AggR-regulated genes. By using real-time quantitative reverse transcription-PCR, we showed that aggR expression in the simulator is increased 3- to 10-fold when 042 is grown under low-pH (5.5 to 6.0) conditions, compared with results with neutral pH (7.0). Interestingly, however, this effect was seen only when the strain was grown in the presence of commensal bacteria. We also found that expression of aggR is 10- to 20-fold higher at low NaCl concentrations, and this effect was also observed only in the presence of commensal bacteria. Using coculture and conditioned-media experiments, we identified specific strains of Enterococcus and Clostridium that upregulated aggR expression; in contrast, strains of Lactobacillus and Veillonella downregulated aggR expression. Our data provide new insights into regulation of virulence genes in EAEC and suggest the utility of intestinal simulation cultures in characterizing enteric gene regulation.

Damaging effect of the fish pathogen Aeromonas salmonicida ssp. salmonicida on intestinal enterocytes of Atlantic salmon (Salmo salar L.)

In fish, bacterial pathogens can enter the host by one or more of three different routes: (a) skin, (b) gills and (c) gastrointestinal tract. Bacteria can cross the gastrointestinal lining in three different ways. In undamaged tissue, bacteria can translocate by transcellular or paracellular routes. Alternatively, bacteria can damage the intestinal lining with extracellular enzymes or toxins before entering. Using an in vitro (Ussing chamber) model, this paper describes intestinal cell damage in Atlantic salmon (Salmo salar L.) caused by the fish pathogen Aeromonas salmonicida ssp. salmonicida, the causative agent of furunculosis. The in vitro method clearly demonstrated substantial detachment of enterocytes from anterior region of the intestine (foregut) upon exposure to the pathogen. In the hindgut (posterior part of the intestine), little detachment was observed but cellular damage involved microvilli, desmosomes and tight junctions. Based on these findings, we suggest that A. salmonicida may obtain entry to the fish by seriously damaging the intestinal lining. Translocation of bacteria through the foregut (rather than the hindgut) is a more likely infection route for A. salmonicida infections in Atlantic salmon.