Pathogenesis of Shiga-Toxin Producing Escherichia coli

Baicalin inhibits the lethality of Shiga-like toxin 2 in mice

Shiga-like toxins (Stxs), produced by pathogenic Escherichia coli, are a major virulence factor involved in severe diseases in human and animals. These toxins are ribosome-inactivating proteins, and treatment for diseases caused by them is not available. Therefore, there is an urgent need for agents capable of effectively targeting this lethal toxin. In this study, we identified baicalin, a flavonoid compound used in Chinese traditional medicine, as a compound against Shiga-like toxin 2 (Stx2). We found that baicalin significantly improves renal function and reduces Stx2-induced lethality in mice. Further experiments revealed that baicalin induces the formation of oligomers by the toxin by direct binding. We also identified the residues important for such interactions and analyzed their roles in binding baicalin by biophysical and biochemical analyses. Our results establish baicalin as a candidate compound for the development of therapeutics against diseases caused by Stxs.

Shiga toxin-producing escherichia coli infections in Norway, 1992-2012: characterization of isolates and identification of risk factors for haemolytic uremic syndrome

BACKGROUND

Shiga toxin-producing E. coli (STEC) infection is associated with haemolytic uremic syndrome (HUS). Therefore Norway has implemented strict guidelines for prevention and control of STEC infection. However, only a subgroup of STEC leads to HUS. Thus, identification of determinants differentiating high risk STEC (HUS STEC) from low risk STEC (non-HUS STEC) is needed to enable implementation of graded infectious disease response.

METHODS

A national study of 333 STEC infections in Norway, including one STEC from each patient or outbreak over two decades (1992-2012), was conducted. Serotype, virulence profile, and genotype of each STEC were determined by phenotypic or PCR based methods. The association between microbiological properties and demographic and clinical data was assessed by univariable analyses and multiple logistic regression models.

RESULTS

From 1992 through 2012, an increased number of STEC cases including more domestically acquired infections were notified in Norway. O157 was the most frequent serogroup (33.6 %), although a decrease of this serogroup was seen over the last decade. All 25 HUS patients yielded STEC with stx2, eae, and ehxA. In a multiple logistic regression model, age ≤5 years (OR = 16.7) and stx2a (OR = 30.1) were independently related to increased risk of HUS. eae and hospitalization could not be modelled since all HUS patients showed these traits. The combination of low age (≤5 years) and the presence of stx2a, and eae gave a positive predictive value (PPV) for HUS of 67.5 % and a negative predictive value (NPV) of 99.0 %. SF O157:[H7] and O145:H?, although associated with HUS in the univariable analyses, were not independent risk factors. stx1 (OR = 0.1) was the sole factor independently associated with a reduced risk of HUS (NPV: 79.7 %); stx2c was not so.

CONCLUSIONS

Our results indicate that virulence gene profile and patients' age are the major determinants of HUS development.

[Acute diarrheal disease caused by enteropathogenic Escherichia coli in Colombia]

Intestinal Escherichia coli pathogens are leading causes of acute diarrheal disease in children less than 5 years in Latin America, Africa and Asia and a leading cause of death in children living in poorest communities in Africa and South East Asia. Studies on the role of E. coli pathogens in childhood diarrhea in Colombia and other countries in Latin America are limited due to the lack of detection assays in clinical laboratories at the main urban medical centers. Recent studies report that enterotoxigenic E. coli is the most common E. coli pathogens associated with diarrhea in children less than 5 years of age. Other E. coli pathotypes have been detected in children with diarrhea including enteropathogenic, enteroaggregative, shiga-toxin producing and diffusely adherent E. coli. It was also found that meat and vegetables at retail stores are contaminated with Shiga-toxin producing E. coli and enteroaggregative E. coli, suggesting that food products are involved in transmission and infection of the susceptible host. More studies are necessary to evaluate the mechanisms of transmission, the impact on the epidemiology of diarrheal disease, and management strategies and prevention of these pathogens affecting the pediatric population in Colombia.

Alteration of the Microbiota and Virulence Gene Expression in E. coli O157:H7 in Pig Ligated Intestine with and without AE Lesions

BACKGROUND

Previously we found that E. coli O157:H7 inoculated into ligated pig intestine formed attaching and effacing (AE) lesions in some pigs but not in others. The present study evaluated changes in the microbial community and in virulence gene expression in E. coli O157:H7 in ligated pig intestine in which the bacteria formed AE lesions or failed to form AE lesions.

METHODOLOGY/PRINCIPAL FINDINGS

The intestinal microbiota was assessed by RNA-based denaturing gradient gel electrophoresis (DGGE) analysis. The DGGE banding patterns showed distinct differences involving two bands which had increased intensity specifically in AE-negative pigs (AE- bands) and several bands which were more abundant in AE-positive pigs. Sequence analysis revealed that the two AE- bands belonged to Veillonella caviae, a species with probiotic properties, and Bacteroides sp. Concurrent with the differences in microbiota, gene expression analysis by quantitative PCR showed that, compared with AE negative pigs, E. coli O157:H7 in AE positive pigs had upregulated genes for putative adhesins, non-LEE encoded nleA and quorum sensing qseF, acid resistance gene ureD, and genes from the locus of enterocyte effacement (LEE).

CONCLUSIONS/SIGNIFICANCE

The present study demonstrated that AE-positive pigs had reduced activities or populations of Veillonella caviae and Bacterioides sp. compared with AE-negative pigs. Further studies are required to understand how the microbiota was changed and the role of these organisms in the control of E. coli O157:H7.

Pro-Coagulant Endothelial Dysfunction Results from EHEC Shiga Toxins and Host Damage-Associated Molecular Patterns

Hemolytic uremic syndrome (HUS) from enterohemorrhagic Escherichia coli infection is a leading cause of kidney failure in otherwise healthy U.S. children. The bacterial Shiga toxins (Stx) induce the characteristic coagulopathy of HUS, but the damage to toxin-receptor expressing cells and organ injury due to ischemia likely also releases inflammatory damage-associated molecular patterns (DAMPs), which may exacerbate injury along with the toxins. To examine this, human aortic and renal glomerular cell anti-coagulant and barrier functions were studied after in vitro challenge with Stx1, Stx2, and DAMPs. There was significant loss of surface anti-coagulant protein C pathway molecules, increased expression of pro-thrombotic PAR1 and reduced protein C activation capability by 15-27%. Histones nearly completely prevented the activated protein C protection of endothelial cells from thrombin-induced permeability. In mice, lethal Stx2 challenge elevated plasma HMGB1 (day 2, 321 ± 118%; p < 0.01) and extracellular histones (day 3, 158 ± 62%; p < 0.01). Mice colonized with Stx2-expressing Citrobacter rodentium developed increased HMGB1 (day 5, 155 ± 55%; p < 0.01) and histones (day 3, 378 ± 188%; p < 0.01). Anti-histone antibody reduced both DAMPs to baseline, but was not sufficient to improve survival outcome or kidney function. Together, these data suggest a potential role Stx to produce DAMPs, and DAMPs to produce endothelial injury and a pro-thrombotic environment.

Approaches to treatment of emerging Shiga toxin-producing Escherichia coli infections highlighting the O104:H4 serotype

Shiga toxin-producing Escherichia coli (STEC) are a group of diarrheagenic bacteria associated with foodborne outbreaks. Infection with these agents may result in grave sequelae that include fatality. A large number of STEC serotypes has been identified to date. E. coli serotype O104:H4 is an emerging pathogen responsible for a 2011 outbreak in Europe that resulted in over 4000 infections and 50 deaths. STEC pathogenicity is highly reliant on the production of one or more Shiga toxins that can inhibit protein synthesis in host cells resulting in a cytotoxicity that may affect various organ systems. Antimicrobials are usually avoided in the treatment of STEC infections since they are believed to induce bacterial cell lysis and the release of stored toxins. Some antimicrobials have also been reported to enhance toxin synthesis and production from these organisms. Various groups have attempted alternative treatment approaches including the administration of toxin-directed antibodies, toxin-adsorbing polymers, probiotic agents and natural remedies. The utility of antibiotics in treating STEC infections has also been reconsidered in recent years with certain modalities showing promise.

Exploiting the power of OMICS approaches to produce E. coli O157 vaccines

Enterohemorrhagic Escherichia coli (EHEC) strains are well-documented human pathogens and causative agents of diarrheal episodes and hemorrhagic colitis. The serotype O157:H7 is highly virulent and responsible for both outbreaks and sporadic cases of diarrhea. Because antibiotic treatment is contraindicated against this pathogen, development of a human vaccine could be an effective intervention in public health. In our recent Infection and Immunity paper, we applied integrated approaches of in silico genome wide search combined with bioinformatics tools to identify and test O157 vaccine candidates for their protective effect on a murine model of gastrointestinal infection. Using genomic/immunoinformatic approaches that are further described here, we categorized vaccine candidates as high, medium, and low priorities, and demonstrate that some high priority candidates were able to significantly induce Th2 cytokines and reduce EHEC colonization. Using the STRING database, we have recently evaluated the vaccine candidates and predict functional protein interactions, determining whether correlations exist for the development of a multi-subunit vaccine, targeting different pathways against EHEC O157:H7. The overall approach is designed to screen potential vaccine candidates against EHEC; however, the methodology can be quickly applied to many other intestinal pathogens.

Clinical Studies of Escherichia coli O157:H7 Conjugate Vaccines in Adults and Young Children

Pediatric immunization has been the most effective measure to prevent and reduce the burden of infectious diseases in children. The recent inclusion of pneumococcal and meningococcal polysaccharide conjugates in infant immunization further reinforces their importance. Currently there is no human vaccine against enterohemorrhagic Escherichia coli (EHEC) infections. This review focuses on the human EHEC vaccine that has been studied clinically, in particular, the polysaccharide conjugate against E. coli O157. The surface polysaccharide antigen, O-specific polysaccharide, was linked to rEPA, recombinant exotoxin A of Pseudomonas aeruginosa. In adults and children 2 to 5 years old, O157-rEPA conjugates, shown to be safe, induced high levels of antilipopolysaccharide immunoglobulin G with bactericidal activities against E. coli O157, a functional bioassay that mimics the killing of inoculum in vivo. A similar construct using the B subunit of Shiga toxin (Stx) 1 as the carrier protein elicited both bactericidal and toxin-neutralizing antibodies in mice. So far there is no clinical study of Stx-based human vaccine. Passive immunization of Stx-specific antibodies with humanized, chimeric, or human monoclonal antibodies, produced in transgenic mice, showed promising data in animal models and offered high prospects. Demonstrations of their safety and effectiveness in treating hemolytic-uremic syndrome or patients with EHEC infections are under way, and results are much anticipated. For future development, other virulence factors such as the nontoxic Stx B subunit or intimin should be included, either as carrier protein in conjugates or as independent components. The additional antigens from O157 may provide broader coverage to non-O157 Stx-producing E. coli and facilitate both preventive and therapeutic treatment.

The ether lipid precursor hexadecylglycerol protects against Shiga toxins

Shiga toxin-producing Escherichia coli bacteria cause hemorrhagic colitis and hemolytic uremic syndrome in humans. Currently, only supportive treatment is available for diagnosed patients. We show here that 24-h pretreatment with an ether lipid precursor, the alkylglycerol sn-1-O-hexadecylglycerol (HG), protects HEp-2 cells against Shiga toxin and Shiga toxin 2. Also the endothelial cell lines HMEC-1 and HBMEC are protected against Shiga toxins after HG pretreatment. In contrast, the corresponding acylglycerol, DL-α-palmitin, has no effect on Shiga toxicity. Although HG treatment provides a strong protection (~30 times higher IC₅₀) against Shiga toxin, only a moderate reduction in toxin binding was observed, suggesting that retrograde transport of the toxin from the plasma membrane to the cytosol is perturbed. Furthermore, endocytosis of Shiga toxin and retrograde sorting from endosomes to the Golgi apparatus remain intact, but transport from the Golgi to the endoplasmic reticulum is inhibited by HG treatment. As previously described, HG reduces the total level of all quantified glycosphingolipids to 50-70% of control, including the Shiga toxin receptor globotriaosylceramide (Gb3), in HEp-2 cells. In accordance with this, we find that interfering with Gb3 biosynthesis by siRNA-mediated knockdown of Gb3 synthase for 24 h causes a similar cytotoxic protection and only a moderate reduction in toxin binding (to 70% of control cells). Alkylglycerols, including HG, have been administered to humans for investigation of therapeutic roles in disorders where ether lipid biosynthesis is deficient, as well as in cancer therapy. Further studies may reveal if HG can also have a therapeutic potential in Shiga toxin-producing E. coli infections.

Characterization of urinary tract infection-associated Shiga toxin-producing Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC), a subgroup of Shiga toxin (Stx)-producing E. coli (STEC), is a leading cause of diarrhea and hemolytic-uremic syndrome (HUS) in humans. However, urinary tract infections (UTIs) caused by this microorganism but not associated with diarrhea have occasionally been reported. We geno- and phenotypically characterized three EHEC isolates obtained from the urine of hospitalized patients suffering from UTIs. These isolates carried typical EHEC virulence markers and belonged to HUS-associated E. coli (HUSEC) clones, but they lacked virulence markers typical of uropathogenic E. coli. One isolate exhibited a localized adherence (LA)-like pattern on T24 urinary bladder epithelial cells. Since the glycosphingolipids (GSLs) globotriaosylceramide (Gb3Cer) and globotetraosylceramide (Gb4Cer) are well-known receptors for Stx but also for P fimbriae, a major virulence factor of extraintestinal pathogenic E. coli (ExPEC), the expression of Gb3Cer and Gb4Cer by T24 cells and in murine urinary bladder tissue was examined by thin-layer chromatography and mass spectrometry. We provide data indicating that Stxs released by the EHEC isolates bind to Gb3Cer and Gb4Cer isolated from T24 cells, which were susceptible to Stx. All three EHEC isolates expressed stx genes upon growth in urine. Two strains were able to cause UTI in a murine infection model and could not be outcompeted in urine in vitro by typical uropathogenic E. coli isolates. Our results indicate that despite the lack of ExPEC virulence markers, EHEC variants may exhibit in certain suitable hosts, e.g., in hospital patients, a uropathogenic potential. The contribution of EHEC virulence factors to uropathogenesis remains to be further investigated.

Diverse virulence gene content of Shiga toxin-producing Escherichia coli from finishing swine

Shiga toxin-producing Escherichia coli (STEC) infections are a critical public health concern because they can cause severe clinical outcomes, such as hemolytic uremic syndrome, in humans. Determining the presence or absence of virulence genes is essential in assessing the potential pathogenicity of STEC strains. Currently, there is limited information about the virulence genes carried by swine STEC strains; therefore, this study was conducted to examine the presence and absence of 69 virulence genes in STEC strains recovered previously from finishing swine in a longitudinal study. A subset of STEC strains was analyzed by pulsed-field gel electrophoresis (PFGE) to examine their genetic relatedness. Swine STEC strains (n = 150) were analyzed by the use of a high-throughput real-time PCR array system, which included 69 virulence gene targets. Three major pathotypes consisted of 16 different combinations of virulence gene profiles, and serotypes were determined in the swine STEC strains. The majority of the swine STEC strains (n = 120) belonged to serotype O59:H21 and carried the same virulence gene profile, which consisted of 9 virulence genes: stx2e, iha, ecs1763, lpfAO113, estIa (STa), ehaA, paa, terE, and ureD. The eae, nleF, and nleH1-2 genes were detected in one swine STEC strain (O49:H21). Other genes encoding adhesins, including iha, were identified (n = 149). The PFGE results demonstrated that swine STEC strains from pigs raised in the same finishing barn were closely related. Our results revealed diverse virulence gene contents among the members of the swine STEC population and enhance understanding of the dynamics of transmission of STEC strains among pigs housed in the same barn.

Glycolipid binding preferences of Shiga toxin variants

The major virulence factor of Shiga toxin producing E. coli, is Shiga toxin (Stx), an AB5 toxin that consists of a ribosomal RNA-cleaving A-subunit surrounded by a pentamer of receptor-binding B subunits. The two major isoforms, Stx1 and Stx2, and Stx2 variants (Stx2a-h) significantly differ in toxicity. The exact reason for this toxicity difference is unknown, however different receptor binding preferences are speculated to play a role. Previous studies used enzyme linked immunosorbent assay (ELISA) to study binding of Stx1 and Stx2a toxoids to glycolipid receptors. Here, we studied binding of holotoxin and B-subunits of Stx1, Stx2a, Stx2b, Stx2c and Stx2d to glycolipid receptors globotriaosylceramide (Gb3) and globotetraosylceramide (Gb4) in the presence of cell membrane components such as phosphatidylcholine (PC), cholesterol (Ch) and other neutral glycolipids. In the absence of PC and Ch, holotoxins of Stx2 variants bound to mixtures of Gb3 with other glycolipids but not to Gb3 or Gb4 alone. Binding of all Stx holotoxins significantly increased in the presence of PC and Ch. Previously, Stx2a has been shown to form a less stable B-pentamer compared to Stx1. However, its effect on glycolipid receptor binding is unknown. In this study, we showed that even in the absence of the A-subunit, the B-subunits of both Stx1 and Stx2a were able to bind to the glycolipids and the more stable B-pentamer formed by Stx1 bound better than the less stable pentamer of Stx2a. B-subunit mutant of Stx1 L41Q, which shows similar stability as Stx2a B-subunits, lacked glycolipid binding, suggesting that pentamerization is more critical for binding of Stx1 than Stx2a.

Emerging types of Shiga toxin-producing E. coli (STEC) O178 present in cattle, deer, and humans from Argentina and Germany

More than 400 serotypes of Shiga toxin-producing Escherichia coli (STEC) have been implicated in outbreaks and sporadic human diseases. In recent years STEC strains belonging to serogroup O178 have been commonly isolated from cattle and food of bovine origin in South America and Europe. In order to explore the significance of these STEC strains as potential human pathogens, 74 German and Argentinean E. coli O178 strains from animals, food and humans were characterized phenotypically and investigated for their serotypes, stx-genotypes and 43 virulence-associated markers by a real-time PCR-microarray. The majority (n = 66) of the O178 strains belonged to serotype O178:H19. The remaining strains divided into O178:H7 (n = 6), O178:H10 (n = 1), and O178:H16 (n = 1). STEC O178:H19 strains were mainly isolated from cattle and food of bovine origin, but one strain was from a patient with hemolytic uremic syndrome (HUS). Genotyping of the STEC O178:H19 strains by pulsed-field gel electrophoresis revealed two major clusters of genetically highly related strains which differ in their stx-genotypes and non-Stx putative virulence traits, including adhesins, toxins, and serine-proteases. Cluster A-strains including the HUS-strain (n = 35) carried genes associated with severe disease in humans (stx2a, stx2d, ehxA, saa, subAB1, lpfAO113 , terE combined with stx1a, espP, iha). Cluster B-strains (n = 26) showed a limited repertoire of virulence genes (stx2c, pagC, lpfAO113 , espP, iha). Among O178:H7 strains isolated from deer meat and patients with uncomplicated disease a new STEC variant was detected that is associated with the genotype stx1c/stx2b/ehxA/subAB2/espI/[terE]/espP/iha. None of the STEC O178 strains was positive for locus of enterocyte effacement (LEE)- and nle-genes. Results indicate that STEC O178:H19 strains belong to the growing group of LEE-negative STEC that should be considered with respect to their potential to cause diseases in humans.

PCR-based detection and molecular characterization of shiga toxin-producing Escherichia coli strains in a routine microbiology laboratory over 16 years

Shiga toxin-producing Escherichia coli (STEC) is a heterogeneous group of bacteria causing disease ranging from asymptomatic carriage and mild infection to hemolytic uremic syndrome (HUS). Here, we describe patients with STEC infection and characterize the STEC strains detected in our laboratory by use of PCR for stx1, stx2, and eae from 1996 through 2011. Patient information was collected from referral forms and from the Norwegian Surveillance System for Communicable Diseases. STEC isolates were characterized with respect to serogroup or serotype, selected potential virulence genes, and multilocus variable-number tandem-repeat analysis (MLVA) genotype. STEC strains were isolated from 138 (1.09%) of 12,651 patients tested. STEC strains of serogroups O26, O103, O121, O145, and O157 were the most frequent. These serogroups, except non-sorbitol-fermenting O157, were also the most frequent among the 11 patients (all ≤5 years old) who developed HUS. Twenty-four STEC strains were classified as being HUS associated based on an epidemiological link to a HUS case, including an MLVA genotype identical to that of the STEC strain. The age of the patient (≤5 years) and the genes eae and stx2a were significantly associated with HUS-associated STEC (P < 0.05 for each parameter), while stx1 was associated with non-HUS-associated STEC (P < 0.05). All of the potential virulence genes analyzed, except ehxA, were significantly more frequent among HUS-associated than non-HUS-associated strains (P < 0.05 for each gene). However, these genes were also present in some non-HUS-associated STEC strains and could therefore not reliably differentiate between HUS-associated and non-HUS-associated STEC strains.

Therapeutic use of a receptor mimic probiotic reduces intestinal Shiga toxin levels in a piglet model of hemolytic uremic syndrome

Background

Hemolytic uremic syndrome (HUS) is a systemic and potentially fatal complication of gastroenteritis secondary to Shiga toxin-producing enterohemorrhagic Escherichia coli (EHEC) infection characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute renal damage. Shiga toxin (Stx), the toxin principle in HUS, is produced locally within the gut following EHEC colonization and is disseminated via the vasculature. Clinical development of HUS currently has no effective treatment and is a leading cause of renal failure in children. Novel post-exposure therapies are currently needed for HUS; therefore, the purpose of this study was to investigate the efficacy of a Stx receptor mimic probiotic in a porcine model of HUS. Edema disease, an infection of swine caused by host adapted Shiga toxin-producing Escherichia coli (STEC) and mediated by Shiga toxin 2e (Stx2e), shares many pathogenic similarities to HUS. In this study, three-week old piglets were inoculated with STEC and 24 hours later treated twice daily with a probiotic expressing an oligosaccharide receptor mimic for Stx2e to determine if the probiotic could reduce intestinal toxin levels.

Methods

Piglets were orally inoculated with 10¹⁰ CFU of STEC strain S1191 eight days after weaning. Beginning day 1 post-inoculation, piglets were treated orally twice daily with 5 × 10¹¹ CFU of either the receptor mimic probiotic or a sham probiotic for 10 days. Intestinal Stx2e levels were assessed daily via Vero cell assay. The efficacy of the probiotic at reducing intestinal Stx2e, vascular lesions, and clinical disease was evaluated with repeated measures ANOVA and Fisher’s exact test as appropriate.

Results

The probiotic significantly reduced intestinal Stx2e, as reflected by decreased fecal toxin titers on days 3–8 post-inoculation (p < 0.01). Despite this reduction in intestinal toxin levels, however, the probiotic failed to reduce the incidence of vascular necrosis in target organs and had no effect on clinical disease.

Conclusions

The data suggest that post-exposure treatment with a Stx-binding probiotic is effective in reducing intestinal toxin burden. Future studies could target this approach for possible development of post-exposure interventions.

The ability of an attaching and effacing pathogen to trigger localized actin assembly contributes to virulence by promoting mucosal attachment

Enterohaemorrhagic Escherichia coli (EHEC) colonizes the intestine and causes bloody diarrhoea and kidney failure by producing Shiga toxin. Upon binding intestinal cells, EHEC triggers a change in host cell shape, generating actin 'pedestals' beneath bound bacteria. To investigate the importance of pedestal formation to disease, we infected genetically engineered mice incapable of supporting pedestal formation by an EHEC-like mouse pathogen, or wild type mice with a mutant of that pathogen incapable of generating pedestals. We found that pedestal formation promotes attachment of bacteria to the intestinal mucosa and vastly increases the severity of Shiga toxin-mediated disease.

Implications of free Shiga toxin-converting bacteriophages occurring outside bacteria for the evolution and the detection of Shiga toxin-producing Escherichia coli

In this review we highlight recent work that has increased our understanding of the distribution of Shiga toxin-converting phages that can be detected as free phage particles, independently of Shiga toxin-producing bacteria (STEC). Stx phages are a quite diverse group of temperate phages that can be found in their prophage state inserted within the STEC chromosome, but can also be found as phages released from the cell after activation of their lytic cycle. They have been detected in extraintestinal environments such as water polluted with feces from humans or animals, food samples or even in stool samples of healthy individuals. The high persistence of phages to several inactivation conditions makes them suitable candidates for the successful mobilization of stx genes, possibly resulting in the genes reaching a new bacterial genomic background by means of transduction, where ultimately they may be expressed, leading to Stx production. Besides the obvious fact that Stx phages circulating between bacteria can be, and probably are, involved in the emergence of new STEC strains, we review here other possible ways in which free Stx phages could interfere with the detection of STEC in a given sample by current laboratory methods and how to avoid such interference.

Host inflammatory response inhibits Escherichia coli O157:H7 adhesion to gut epithelium through augmentation of mucin expression

Escherichia coli O157:H7, a major Shiga toxin-producing pathogen, has a low infectious dose and causes serious illness in humans. The gastrointestinal tract of cattle is the primary reservoir of E. coli O157:H7, and thus, it is critical to eliminate or reduce E. coli O157:H7 gut colonization. Given that E. coli O157:H7 produces effectors that attenuate inflammatory signaling, we hypothesized that the host inflammatory response acts to perturb E. coli O157:H7 intestinal colonization. Tumor necrosis factor alpha (TNF-α) treatment of HT-29 cells resulted in increased expression of inflammatory cytokine interleukin 1β (IL-1β), IL-8, and TNF-α genes and increased IL-8 protein and resulted in decreased adhesion of E. coli O157:H7. Similarly, E. coli O157:H7 adhesion to cattle colonic explants was reduced by TNF-α treatment. Irrespective of the presence of E. coli O157:H7, TNF-α enhanced activation of p65, the key mediator of NF-κB inflammatory signaling, whereas E. coli O157:H7 infection suppressed this pathway by inhibiting p65 activation in HT-29 cells. To further explore the mechanisms linking the inflammatory response to attenuated E. coli O157:H7 adhesion, mucin 2 (MUC2) expression was analyzed, considering that the intestinal mucus layer is the first defense against enteric pathogens and MUC2 is the major secretory mucin in the intestine. MUC2 expression in HT-29 cells was increased by TNF-α treatment and by E. coli O157:H7 infection. However, reducing mucin expression by blocking mitogen-activated protein kinase (MAPK) extracellular signal-regulated protein kinases 1/2 (ERK1/2) and/or phosphatidylinositol 3-kinase (PI3K)/Akt signaling increased E. coli O157:H7 adherence to HT-29 cells. These data suggest that the inflammatory cytokine response acts to protect host epithelial cells against E. coli O157:H7 colonization, at least in part, by promoting mucin production.

Pathogenicity, host responses and implications for management of enterohemorrhagic Escherichia coli O157:H7 infection

Enterohemorrhagic Escherichia coli serotype O157:H7 is a food- and waterborne pathogen that causes significant morbidity and mortality in both developing and industrialized nations. The present review focuses on the history, epidemiology and evolution of the pathogen; provides a mechanistic overview of major virulence factors (including Shiga toxins, locus of enterocyte effacement pathogenicity island and pO157 plasmid); discusses host immune responses to infection; considers available animal models; and provides an overview of current and potential future management considerations.

Chronic sequelae of E. coli O157: systematic review and meta-analysis of the proportion of E. coli O157 cases that develop chronic sequelae

OBJECTIVE

This was a systematic review and meta-analysis to determine the proportion of Escherichia coli O157 cases that develop chronic sequelae.

DATA SOURCES

We conducted a systematic review of articles published prior to July 2011 in Pubmed, Agricola, CabDirect, or Food Safety and Technology Abstracts.

STUDY SELECTION

Studies were selected that reported the number of E. coli O157 cases that developed reactive arthritis (ReA), hemolytic uremic syndrome (HUS), irritable bowel syndrome, inflammatory bowel disease, or Guillain Barré syndrome.

METHODS

Three levels of screening and data extraction of articles were conducted using predefined data fields. Meta-analysis was performed on unique outcome measures using a random-effects model, and heterogeneity was assessed using the I² value. Meta-regression was used to explore the influence of nine study-level variables on heterogeneity.

RESULTS

A total of 82 studies were identified reporting 141 different outcome measures; 81 reported on HUS and one reported on ReA. Depending on the number of cases of E. coli O157, the estimate for the proportion of E. coli O157 cases that develop HUS ranged from 17.2% in extra-small studies (<50 cases) to 4.2% in extra-large studies (>1000 cases). Heterogeneity was significantly associated with group size (p<0.0001); however, the majority of the heterogeneity was unexplained.

CONCLUSIONS

High unexplained heterogeneity indicated that the study-level factors examined had a minimal influence on the variation of estimates reported.

Virulence profiling of Shiga toxin-producing Escherichia coli recovered from domestic farm animals in Northwestern Mexico

Shiga toxin-producing Escherichia coli (STEC) is a zoonotic enteric pathogen that causes human gastrointestinal illnesses. The present study characterized the virulence profiles of O157 and non-O157 STEC strains, recovered from domestic animals in small rural farms within the agricultural Culiacan Valley in Mexico. Virulence genes coding for adhesins, cytotoxins, proteases, subtypes of Shiga toxin (Stx), and other effectors were identified in the STEC strains by PCR. The genotyping analysis revealed the presence of the effectors nleA, nleB, nleE, and nleH1-2, espK, and espN in the O157:H7 and O111:H8 STEC strains. Furthermore, the genes encoding the autoagglutinating adhesin (Saa) and subtilase (SubA) were exclusively identified in the O8:H19 eae-negative strains. The adhesin (iha) and the silent hemolysin (sheA) genes were detected in 79% of the O157 and non-O157 strains. To examine the relative toxicities of the STEC strains, a fluorescent Vero cell line, Vero-d2EGFPs, was employed to measure the inhibition of protein synthesis by Stx. Analysis of culture supernatants from serotype O8:H19 strains with the stx gene profile stx_1a, stx_2a, and stx_2c and serotypes O75:H8 and O146:H8 strains with the stx gene profile stx_1a, stx_1c, and stx_2b, resulted in a significant reduction in the Vero-d2EGFP fluorescent signal. These observations suggest that these non-O157 strains may have an enhanced ability to inhibit protein synthesis in Vero cells. Interestingly, analysis of the stx_2c-positive O157:H7 strains resulted in a high fluorescent signal, indicating a reduced toxicity in the Vero-d2EGFP cells. These findings indicate that the O157 and non-O157 STEC strains, recovered in the Culiacan Valley, display distinct virulence profiles and relative toxicities in mammalian cells and have provided information for evaluating risks associated with zoonotic STEC in this agricultural region in Mexico.

Persistence of infectious Shiga toxin-encoding bacteriophages after disinfection treatments

In Shiga toxin-producing Escherichia coli (STEC), induction of Shiga toxin-encoding bacteriophages (Stx phages) causes the release of free phages that can later be found in the environment. The ability of Stx phages to survive different inactivation conditions determines their prevalence in the environment, the risk of stx transduction, and the generation of new STEC strains. We evaluated the infectivity and genomes of two Stx phages (Φ534 and Φ557) under different conditions. Infectious Stx phages were stable at 4, 22, and 37°C and at pH 7 and 9 after 1 month of storage but were completely inactivated at pH 3. Infective Stx phages decreased moderately when treated with UV (2.2-log10 reduction for an estimated UV dose of 178.2 mJ/cm(2)) or after treatment at 60 and 68°C for 60 min (2.2- and 2.5-log10 reductions, respectively) and were highly inactivated (3 log10) by 10 ppm of chlorine in 1 min. Assays in a mesocosm showed lower inactivation of all microorganisms in winter than in summer. The number of Stx phage genomes did not decrease significantly in most cases, and STEC inactivation was higher than phage inactivation under all conditions. Moreover, Stx phages retained the ability to lysogenize E. coli after some of the treatments.

Fast structural responses of gap junction membrane domains to AB5 toxins

Gap junctions (GJs) represent connexin-rich membrane domains that connect interiors of adjoining cells in mammalian tissues. How fast GJs can respond to bacterial pathogens has not been known previously. Using Bessel beam plane illumination and confocal spinning disk microscopy, we found fast (~500 ms) formation of connexin-depleted regions (CDRs) inside GJ plaques between cells exposed to AB5 toxins. CDR formation appears as a fast redistribution of connexin channels within GJ plaques with minor changes in outline or geometry. CDR formation does not depend on membrane trafficking or submembrane cytoskeleton and has no effect on GJ conductance. However, CDR responses depend on membrane lipids, can be modified by cholesterol-clustering agents and extracellular K(+) ion concentration, and influence cAMP signaling. The CDR response of GJ plaques to bacterial toxins is a phenomenon observed for all tested connexin isoforms. Through signaling, the CDR response may enable cells to sense exposure to AB5 toxins. CDR formation may reflect lipid-phase separation events in the biological membrane of the GJ plaque, leading to increased connexin packing and lipid reorganization. Our data demonstrate very fast dynamics (in the millisecond-to-second range) within GJ plaques, which previously were considered to be relatively stable, long-lived structures.

A single VHH-based toxin-neutralizing agent and an effector antibody protect mice against challenge with Shiga toxins 1 and 2

Shiga toxin-producing Escherichia coli (STEC) is a major cause of severe food-borne disease worldwide, and two Shiga toxins, Stx1 and Stx2, are primarily responsible for the serious disease consequence, hemolytic-uremic syndrome (HUS). Here we report identification of a panel of heavy-chain-only antibody (Ab) V(H) (VHH) domains that neutralize Stx1 and/or Stx2 in cell-based assays. VHH heterodimer toxin-neutralizing agents containing two linked Stx1-neutralizing VHHs or two Stx2-neutralizing VHHs were generally much more potent at Stx neutralization than a pool of the two-component monomers tested in cell-based assays and in vivo mouse models. We recently reported that clearance of toxins can be promoted by coadministering a VHH-based toxin-neutralizing agent with an antitag monoclonal antibody (MAb), called the "effector Ab," that indirectly decorates each toxin molecule with four Ab molecules. Decoration occurs because the Ab binds to a common epitopic tag present at two sites on each of the two VHH heterodimer molecules that bind to each toxin molecule. Here we show that coadministration of effector Ab substantially improved the efficacy of Stx toxin-neutralizing agents to prevent death or kidney damage in mice following challenge with Stx1 or Stx2. A single toxin-neutralizing agent consisting of a double-tagged VHH heterotrimer--one Stx1-specific VHH, one Stx2-specific VHH, and one Stx1/Stx2 cross-specific VHH--was effective in preventing all symptoms of intoxication from Stx1 and Stx2 when coadministered with effector Ab. Overall, the availability of simple, defined, recombinant proteins that provide cost-effective protection against HUS opens up new therapeutic approaches to managing disease.

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.

Serine protease EspP from enterohemorrhagic Escherichia coli is sufficient to induce shiga toxin macropinocytosis in intestinal epithelium

Life-threatening intestinal and systemic effects of the Shiga toxins produced by enterohemorrhagic Escherichia coli (EHEC) require toxin uptake and transcytosis across intestinal epithelial cells. We have recently demonstrated that EHEC infection of intestinal epithelial cells stimulates toxin macropinocytosis, an actin-dependent endocytic pathway. Host actin rearrangement necessary for EHEC attachment to enterocytes is mediated by the type 3 secretion system which functions as a molecular syringe to translocate bacterial effector proteins directly into host cells. Actin-dependent EHEC attachment also requires the outer membrane protein intimin, a major EHEC adhesin. Here, we investigate the role of type 3 secretion in actin turnover occurring during toxin macropinocytosis. Toxin macropinocytosis is independent of EHEC type 3 secretion and intimin attachment. EHEC soluble factors are sufficient to stimulate macropinocytosis and deliver toxin into enterocytes in vitro and in vivo; intact bacteria are not required. Intimin-negative enteroaggregative Escherichia coli (EAEC) O104:H4 robustly stimulate Shiga toxin macropinocytosis into intestinal epithelial cells. The apical macropinosomes formed in intestinal epithelial cells move through the cells and release their cargo at these cells' basolateral sides. Further analysis of EHEC secreted proteins shows that a serine protease EspP alone is able to stimulate host actin remodeling and toxin macropinocytosis. The observation that soluble factors, possibly serine proteases including EspP, from each of two genetically distinct toxin-producing strains, can stimulate Shiga toxin macropinocytosis and transcellular transcytosis alters current ideas concerning mechanisms whereby Shiga toxin interacts with human enterocytes. Mechanisms important for this macropinocytic pathway could suggest new potential therapeutic targets for Shiga toxin-induced disease.

Crystal structure of the pilotin from the enterohemorrhagic Escherichia coli type II secretion system

Bacteria contain several sophisticated macromolecular machineries responsible for translocating proteins across the cell envelope. One prominent example is the type II secretion system (T2SS), which contains a large outer membrane channel, called the secretin. These gated channels require specialized proteins, so-called pilotins, to reach and assemble in the outer membrane. Here we report the crystal structure of the pilotin GspS from the T2SS of enterohemorrhagic Escherichia coli (EHEC), an important pathogen that can cause severe disease in cases of food poisoning. In this four-helix protein, the straight helix α2, the curved helix α3 and the bent helix α4 surround the central N-terminal helix α1. The helices of GspS create a prominent groove, mainly formed by side chains of helices α1, α2 and α3. In the EHEC GspS structure this groove is occupied by extra electron density which is reminiscent of an α-helix and corresponds well with a binding site observed in a homologous pilotin. The residues forming the groove are well conserved among homologs, pointing to a key role of this groove in this class of T2SS pilotins. At the same time, T2SS pilotins in different species can be entirely different in structure, and the pilotins for secretins in non-T2SS machineries have yet again unrelated folds, despite a common function. It is striking that a common complex function, such as targeting and assembling an outer membrane multimeric channel, can be performed by proteins with entirely different folds.

Phylogenetic and molecular analysis of food-borne shiga toxin-producing Escherichia coli

Seventy-five food-associated Shiga toxin-producing Escherichia coli (STEC) strains were analyzed by molecular and phylogenetic methods to describe their pathogenic potential. The presence of the locus of proteolysis activity (LPA), the chromosomal pathogenicity island (PAI) PAI ICL3, and the autotransporter-encoding gene sabA was examined by PCR. Furthermore, the occupation of the chromosomal integration sites of the locus of enterocyte effacement (LEE), selC, pheU, and pheV, as well as the Stx phage integration sites yehV, yecE, wrbA, z2577, and ssrA, was analyzed. Moreover, the antibiotic resistance phenotypes of all STEC strains were determined. Multilocus sequence typing (MLST) was performed, and sequence types (STs) and sequence type complexes (STCs) were compared with those of 42 hemolytic-uremic syndrome (HUS)-associated enterohemorrhagic E. coli (HUSEC) strains. Besides 59 STs and 4 STCs, three larger clusters were defined in this strain collection. Clusters A and C consist mostly of highly pathogenic eae-positive HUSEC strains and some related food-borne STEC strains. A member of a new O26 HUS-associated clone and the 2011 outbreak strain E. coli O104:H4 were found in cluster A. Cluster B comprises only eae-negative food-borne STEC strains as well as mainly eae-negative HUSEC strains. Although food-borne strains of cluster B were not clearly associated with disease, serotypes of important pathogens, such as O91:H21 and O113:H21, were in this cluster and closely related to the food-borne strains. Clonal analysis demonstrated eight closely related genetic groups of food-borne STEC and HUSEC strains that shared the same ST and were similar in their virulence gene composition. These groups should be considered with respect to their potential for human infection.

Facing glycosphingolipid-Shiga toxin interaction: dire straits for endothelial cells of the human vasculature

The two major Shiga toxin (Stx) types, Stx1 and Stx2, produced by enterohemorrhagic Escherichia coli (EHEC) in particular injure renal and cerebral microvascular endothelial cells after transfer from the human intestine into the circulation. Stxs are AB(5) toxins composed of an enzymatically active A subunit and the pentameric B subunit, which preferentially binds to the glycosphingolipid globotriaosylceramide (Gb3Cer/CD77). This review summarizes the current knowledge on Stx-caused cellular injury and the structural diversity of Stx receptors as well as the initial molecular interaction of Stxs with the human endothelium of different vascular beds. The varying lipoforms of Stx receptors and their spatial organization in lipid rafts suggest a central role in different modes of receptor-mediated endocytosis and intracellular destiny of the toxins. The design and development of tailored Stx neutralizers targeting the oligosaccharide-toxin recognition event has become a very real prospect to ameliorate or prevent life-threatening renal and neurological complications.

Lysogenic conversion and phage resistance development in phage exposed Escherichia coli biofilms

In this study, three-day old mature biofilms of Escherichia coli were exposed once to either a temperate Shiga-toxin encoding phage (H-19B) or an obligatory lytic phage (T7), after which further dynamics in the biofilm were monitored. As such, it was found that a single dose of H-19B could rapidly lead to a near complete lysogenization of the biofilm, with a subsequent continuous release of infectious H-19B particles. On the other hand, a single dose of T7 rapidly led to resistance development in the biofilm population. Together, our data indicates a profound impact of phages on the dynamics within structured bacterial populations.

Shiga toxins and the pathophysiology of hemolytic uremic syndrome in humans and animals

Food-borne diseases are estimated at 76 million illnesses and 5000 deaths every year in the United States with the greatest burden on young children, the elderly and immunocompromised populations. The impact of efficient food distribution systems and a truly global food supply ensures that outbreaks, previously sporadic and contained locally, are far more widespread and emerging pathogens have far more frequent infection opportunities. Enterohemorrhagic E. coli is an emerging food- and water-borne pathogen family whose Shiga-like toxins induce painful hemorrhagic colitis with potentially lethal complications of hemolytic uremic syndrome (HUS). The clinical manifestations of Shiga toxin-induced HUS overlap with other related syndromes yet molecular mechanisms differ considerably. As discussed herein, understanding these differences and the novel properties of the toxins is imperative for clinical management decisions, design of appropriate animal models, and choices of adjunctive therapeutics. The emergence of new strains with rapidly aggressive virulence makes clinical and research initiatives in this field a high public health priority.

Survival of enterohemorrhagic Escherichia coli in the presence of Acanthamoeba castellanii and its dependence on Pho regulon

Enterohemorrhagic Escherichia coli (EHEC) are involved in outbreaks of food-borne illness and transmitted to humans through bovine products or water contaminated by cattle feces. Microbial interaction is one of the strategies used by pathogenic bacteria to survive in the environment. Among protozoa, the free-living amoebae are known to host and protect several water-borne pathogens. In this study, the interaction between EHEC and the predacious protozoa Acanthamoeba castellanii was investigated. Using monoculture and cocultures, growth of both organisms was estimated for 3 weeks by total and viable cell counts. The numbers of EHEC were significantly higher when cultured with amoebae than without, and less EHEC shifted into a viable but nonculturable state in the presence of amoebae. Using several mutants, we observed that the Pho regulon is required for EHEC growth when cocultured with amoebae. In contrast, the Shiga toxins (Stx) were not involved in this association phenotype. Cocultures monitored by electron microscopy revealed a loss of the regular rod shape of EHEC and the secretion of multilamellar vesicles by the amoebae, which did not contain bacteria. As the interaction between A. castellanii and EHEC appears beneficial for bacterial growth, this supports a potential role for protozoa in promoting the persistence of EHEC in the environment.

A novel murine infection model for Shiga toxin-producing Escherichia coli

Enterohemorrhagic E. coli (EHEC) is an important subset of Shiga toxin-producing (Stx-producing) E. coli (STEC), pathogens that have been implicated in outbreaks of food-borne illness and can cause intestinal and systemic disease, including severe renal damage. Upon attachment to intestinal epithelium, EHEC generates "attaching and effacing" (AE) lesions characterized by intimate attachment and actin rearrangement upon host cell binding. Stx produced in the gut transverses the intestinal epithelium, causing vascular damage that leads to systemic disease. Models of EHEC infection in conventional mice do not manifest key features of disease, such as AE lesions, intestinal damage, and systemic illness. In order to develop an infection model that better reflects the pathogenesis of this subset of STEC, we constructed an Stx-producing strain of Citrobacter rodentium, a murine AE pathogen that otherwise lacks Stx. Mice infected with Stx-producing C. rodentium developed AE lesions on the intestinal epithelium and Stx-dependent intestinal inflammatory damage. Further, the mice experienced lethal infection characterized by histopathological and functional kidney damage. The development of a murine model that encompasses AE lesion formation and Stx-mediated tissue damage will provide a new platform upon which to identify EHEC alterations of host epithelium that contribute to systemic disease.