Expression of receptors for verotoxin 1 from Escherichia coli O157 on bovine intestinal epithelium

A Comprehensive Review on Shiga Toxin Subtypes and Their Niche-Related Distribution Characteristics in Shiga-Toxin-Producing E. coli and Other Bacterial Hosts

Shiga toxin (Stx), the main virulence factor of Shiga-toxin-producing E. coli (STEC), was first discovered in Shigella dysenteriae strains. While several other bacterial species have since been reported to produce Stx, STEC poses the most significant risk to human health due to its widespread prevalence across various animal hosts that have close contact with human populations. Based on its biochemical and molecular characteristics, Shiga toxin can be grouped into two types, Stx1 and Stx2, among which a variety of variants and subtypes have been identified in various bacteria and host species. Interestingly, the different Stx subtypes appear to vary in their host distribution characteristics and in the severity of diseases that they are associated with. As such, this review provides a comprehensive overview on the bacterial species that have been recorded to possess stx genes to date, with a specific focus on the various Stx subtype variants discovered in STEC, their prevalence in certain host species, and their disease-related characteristics. This review provides a better understanding of the Stx subtypes and highlights the need for rapid and accurate approaches to toxin subtyping for the proper evaluation of the health risks associated with Shiga-toxin-related bacterial food contamination and human infections.

Shiga Toxin-Producing Escherichia coli (STEC) Associated with Calf Mortality in Uruguay

In Uruguay, the mortality of dairy calves due to infectious diseases is high. Escherichia coli is a natural inhabitant of the intestinal microbiota, but can cause several infections. The aim of the work was to characterize E. coli isolates from intestinal and extraintestinal origin of dead newborn calves. Using PCR, virulence gene characteristics of pathogenic E. coli were searched. The pathogenic E. coli were molecularly characterized and the phylogroup, serogroup and the Stx subtype were determined. Antibiotic susceptibility was determined using the Kirby-Bauer disk diffusion method and plasmid-mediated quinolone resistance (PMQR) genes with PCR. Finally, clonal relationships were inferred using PFGE. Gene characteristics of the Shiga toxin-producing E. coli (STEC), Enteropathogenic E. coli (EPEC) and Necrotoxigenic E. coli (NTEC) were identified. The prevalence of the iucD, afa8E, f17, papC, stx1, eae and ehxA genes was high and no f5, f41, saa, sfaDE, cdtIV, lt, sta or stx2 were detected. The prevalence of STEC gene stx1 in the dead calves stood out and was higher compared with previous studies conducted in live calves, and STEC LEE+ (Enterohemorrhagic E. coli (EHEC)) isolates with stx1/eae/ehxA genotypes were more frequently identified in the intestinal than in the extraintestinal environment. E. coli isolates were assigned to phylogroups A, B1, D and E, and some belonged to the O111 serogroup. stx1a and stx1c subtypes were determined in STEC. A high prevalence of multi-resistance among STEC and qnrB genes was determined. The PFGE showed a high diversity of pathogenic strains with similar genetic profiles. It can be speculated that EHEC (stx1/eae/ehxA) could play an important role in mortality. The afa8E, f17G1 and papC genes could also have a role in calf mortality. Multidrug resistance defies disease treatment and increases the risk of death, while the potential transmissibility of genes to other species constitutes a threat to public health.

Enterohemorrhagic Escherichia coli and a Fresh View on Shiga Toxin-Binding Glycosphingolipids of Primary Human Kidney and Colon Epithelial Cells and Their Toxin Susceptibility

Enterohemorrhagic Escherichia coli (EHEC) are the human pathogenic subset of Shiga toxin (Stx)-producing E. coli (STEC). EHEC are responsible for severe colon infections associated with life-threatening extraintestinal complications such as the hemolytic-uremic syndrome (HUS) and neurological disturbances. Endothelial cells in various human organs are renowned targets of Stx, whereas the role of epithelial cells of colon and kidneys in the infection process has been and is still a matter of debate. This review shortly addresses the clinical impact of EHEC infections, novel aspects of vesicular package of Stx in the intestine and the blood stream as well as Stx-mediated extraintestinal complications and therapeutic options. Here follows a compilation of the Stx-binding glycosphingolipids (GSLs), globotriaosylceramide (Gb3Cer) and globotetraosylceramide (Gb4Cer) and their various lipoforms present in primary human kidney and colon epithelial cells and their distribution in lipid raft-analog membrane preparations. The last issues are the high and extremely low susceptibility of primary renal and colonic epithelial cells, respectively, suggesting a large resilience of the intestinal epithelium against the human-pathogenic Stx1a- and Stx2a-subtypes due to the low content of the high-affinity Stx-receptor Gb3Cer in colon epithelial cells. The review closes with a brief outlook on future challenges of Stx research.

Transcriptional analysis reveals specific niche factors and response to environmental stresses of enterohemorrhagic Escherichia coli O157:H7 in bovine digestive contents

Background

Enterohemorrhagic Escherichia coli (EHEC) are responsible for severe diseases in humans, and the ruminant digestive tract is considered as their main reservoir. Their excretion in bovine feces leads to the contamination of foods and the environment. Thus, providing knowledge of processes used by EHEC to survive and/or develop all along the bovine gut represents a major step for strategies implementation.

Results

We compared the transcriptome of the reference EHEC strain EDL933 incubated in vitro in triplicate samples in sterile bovine rumen, small intestine and rectum contents with that of the strain grown in an artificial medium using RNA-sequencing (RNA-seq), focusing on genes involved in stress response, adhesion systems including the LEE, iron uptake, motility and chemotaxis. We also compared expression of these genes in one digestive content relative to the others. In addition, we quantified short chain fatty acids and metal ions present in the three digestive contents. RNA-seq data first highlighted response of EHEC EDL933 to unfavorable physiochemical conditions encountered during its transit through the bovine gut lumen. Seventy-eight genes involved in stress responses including drug export, oxidative stress and acid resistance/pH adaptation were over-expressed in all the digestive contents compared with artificial medium. However, differences in stress fitness gene expression were observed depending on the digestive segment, suggesting that these differences were due to distinct physiochemical conditions in the bovine digestive contents. EHEC activated genes encoding three toxin/antitoxin systems in rumen content and many gene clusters involved in motility and chemotaxis in rectum contents. Genes involved in iron uptake and utilization were mostly down-regulated in all digestive contents compared with artificial medium, but feo genes were over-expressed in rumen and small intestine compared with rectum. The five LEE operons were more expressed in rectum than in rumen content, and LEE1 was also more expressed in rectum than in small intestine content.

Conclusion

Our results highlight various strategies that EHEC may implement to survive in the gastrointestinal environment of cattle. These data could also help defining new targets to limit EHEC O157:H7 carriage and shedding by cattle.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02343-7.

Primary Human Colon Epithelial Cells (pHCoEpiCs) Do Express the Shiga Toxin (Stx) Receptor Glycosphingolipids Gb3Cer and Gb4Cer and Are Largely Refractory but Not Resistant towards Stx

Shiga toxin (Stx) is released by enterohemorrhagic Escherichia coli (EHEC) into the human intestinal lumen and transferred across the colon epithelium to the circulation. Stx-mediated damage of human kidney and brain endothelial cells and renal epithelial cells is a renowned feature, while the sensitivity of the human colon epithelium towards Stx and the decoration with the Stx receptor glycosphingolipids (GSLs) globotriaosylceramide (Gb3Cer, Galα1-4Galβ1-4Glcβ1-1Cer) and globotetraosylceramide (Gb4Cer, GalNAcβ1-3Galα1-4Galβ1-4Glcβ1-1Cer) is a matter of debate. Structural analysis of the globo-series GSLs of serum-free cultivated primary human colon epithelial cells (pHCoEpiCs) revealed Gb4Cer as the major neutral GSL with Cer (d18:1, C16:0), Cer (d18:1, C22:1/C22:0) and Cer (d18:1, C24:2/C24:1) accompanied by minor Gb3Cer with Cer (d18:1, C16:0) and Cer (d18:1, C24:1) as the dominant lipoforms. Gb3Cer and Gb4Cer co-distributed with cholesterol and sphingomyelin to detergent-resistant membranes (DRMs) used as microdomain analogs. Exposure to increasing Stx concentrations indicated only a slight cell-damaging effect at the highest toxin concentration of 1 µg/mL for Stx1a and Stx2a, whereas a significant effect was detected for Stx2e. Considerable Stx refractiveness of pHCoEpiCs that correlated with the rather low cellular content of the high-affinity Stx-receptor Gb3Cer renders the human colon epithelium questionable as a major target of Stx1a and Stx2a.

The Role of Escherichia coli Shiga Toxins in STEC Colonization of Cattle

Many cattle are persistently colonized with Shiga toxin-producing Escherichia coli (STEC) and represent a major source of human infections with human-pathogenic STEC strains (syn. enterohemorrhagic E. coli (EHEC)). Intervention strategies most effectively protecting humans best aim at the limitation of bovine STEC shedding. Mechanisms enabling STEC to persist in cattle are only partialy understood. Cattle were long believed to resist the detrimental effects of Shiga toxins (Stxs), potent cytotoxins acting as principal virulence factors in the pathogenesis of human EHEC-associated diseases. However, work by different groups, summarized in this review, has provided substantial evidence that different types of target cells for Stxs exist in cattle. Peripheral and intestinal lymphocytes express the Stx receptor globotriaosylceramide (Gb₃syn. CD77) in vitro and in vivo in an activation-dependent fashion with Stx-binding isoforms expressed predominantly at early stages of the activation process. Subpopulations of colonic epithelial cells and macrophage-like cells, residing in the bovine mucosa in proximity to STEC colonies, are also targeted by Stxs. STEC-inoculated calves are depressed in mounting appropriate cellular immune responses which can be overcome by vaccination of the animals against Stxs early in life before encountering STEC. Considering Stx target cells and the resulting effects of Stxs in cattle, which significantly differ from effects implicated in human disease, may open promising opportunities to improve existing yet insufficient measures to limit STEC carriage and shedding by the principal reservoir host.

Molecular Biology of Escherichia Coli Shiga Toxins' Effects on Mammalian Cells

Shiga toxins (Stxs), syn. Vero(cyto)toxins, are potent bacterial exotoxins and the principal virulence factor of enterohemorrhagic Escherichia coli (EHEC), a subset of Shiga toxin-producing E. coli (STEC). EHEC strains, e.g., strains of serovars O157:H7 and O104:H4, may cause individual cases as well as large outbreaks of life-threatening diseases in humans. Stxs primarily exert a ribotoxic activity in the eukaryotic target cells of the mammalian host resulting in rapid protein synthesis inhibition and cell death. Damage of endothelial cells in the kidneys and the central nervous system by Stxs is central in the pathogenesis of hemolytic uremic syndrome (HUS) in humans and edema disease in pigs. Probably even more important, the toxins also are capable of modulating a plethora of essential cellular functions, which eventually disturb intercellular communication. The review aims at providing a comprehensive overview of the current knowledge of the time course and the consecutive steps of Stx/cell interactions at the molecular level. Intervention measures deduced from an in-depth understanding of this molecular interplay may foster our basic understanding of cellular biology and microbial pathogenesis and pave the way to the creation of host-directed active compounds to mitigate the pathological conditions of STEC infections in the mammalian body.

Shiga toxin sub-type 2a increases the efficiency of Escherichia coli O157 transmission between animals and restricts epithelial regeneration in bovine enteroids

Specific Escherichia coli isolates lysogenised with prophages that express Shiga toxin (Stx) can be a threat to human health, with cattle being an important natural reservoir. In many countries the most severe pathology is associated with enterohaemorrhagic E. coli (EHEC) serogroups that express Stx subtype 2a. In the United Kingdom, phage type (PT) 21/28 O157 strains have emerged as the predominant cause of life-threatening EHEC infections and this phage type commonly encodes both Stx2a and Stx2c toxin types. PT21/28 is also epidemiologically linked to super-shedding (>10³ cfu/g of faeces) which is significant for inter-animal transmission and human infection as demonstrated using modelling studies. We demonstrate that Stx2a is the main toxin produced by stx2a⁺/stx2c⁺ PT21/28 strains induced with mitomycin C and this is associated with more rapid induction of gene expression from the Stx2a-encoding prophage compared to that from the Stx2c-encoding prophage. Bacterial supernatants containing either Stx2a and/or Stx2c were demonstrated to restrict growth of bovine gastrointestinal organoids with no restriction when toxin production was not induced or prevented by mutation. Isogenic strains that differed in their capacity to produce Stx2a were selected for experimental oral colonisation of calves to assess the significance of Stx2a for both super-shedding and transmission between animals. Restoration of Stx2a expression in a PT21/28 background significantly increased animal-to-animal transmission and the number of sentinel animals that became super-shedders. We propose that while both Stx2a and Stx2c can restrict regeneration of the epithelium, it is the relatively rapid and higher levels of Stx2a induction, compared to Stx2c, that have contributed to the successful emergence of Stx2a+ E. coli isolates in cattle in the last 40 years. We propose a model in which Stx2a enhances E. coli O157 colonisation of in-contact animals by restricting regeneration and turnover of the colonised gastrointestinal epithelium.

Enterohaemorrhagic E. coli (EHEC) O157 strains are found in cattle where they are asymptomatic, while human exposure can lead to severe symptoms including bloody diarrhoea and kidney damage due to the activity of Shiga toxin (Stx). The most serious symptoms in humans are associated with isolates that encode Stx subtype 2a. The advantage of these toxins in the animal reservoir is still not clear, however there is experimental evidence implicating Stx with increased bacterial adherence, immune modulation and suppression of predatory protozoa. In this study, the hypothesis that Stx2a is important for super-shedding and calf-to-calf transmission was tested by comparing excretion and transmission dynamics of E. coli O157 strains with and without Stx2a. While Stx2a did not alter excretion levels when calfs were orally challenge, it enabled colonisation of more in contact ‘sentinel’ animals in our transmission model. We show that Stx2a is generally induced more rapidly than Stx2c, resulting in increased levels of Stx2a expression. Both Stx2a and Stx2c were able to restrict cellular proliferation of epithelial cells in cultured bovine enteroids. Taken together, we propose that rapid production of Stx2a and its role in establishing E. coli O157 colonisation in the bovine gastrointestinal tract facilitate effective transmission and have led to its expansion in the cattle E. coli O157 population.

Transcriptomic analysis reveals specific metabolic pathways of enterohemorrhagic Escherichia coli O157:H7 in bovine digestive contents

Background

The cattle gastrointestinal tract (GIT) is the main enterohemorrhagic Escherichia coli (EHEC) reservoir. In order to identify nutrients required for the survival or multiplication of EHEC in the bovine GIT, we compared the transcriptomes of the EHEC O157:H7 reference strain EDL933 cultured in vitro in bovine digestive contents (DCs) (rumen, small intestine and rectum) using RNA-sequencing.

Results

Gene expression profiles showed that EHEC EDL933 activated common but also specific metabolic pathways to survive in the different bovine DCs. Mucus-derived carbohydrates seem important in EHEC nutrition in posterior DCs (small intestine and rectum) but not in rumen content. Additional carbohydrates (xylose, ribose, mannitol, galactitol) as well as gluconeogenic substrates (aspartate, serine, glycerol) would also be used by EHEC as carbon and/or nitrogen sources all along the bovine GIT including the rumen. However, xylose, GalNac, ribose and fucose transport and/or assimilation encoding genes were over-expressed during incubation in rectum content compared with rumen and intestine contents, and genes coding for maltose transport were only induced in rectum. This suggests a role for these carbohydrates in the colonization of the cattle rectum, considered as the major site for EHEC multiplication. In contrast, the transcription of the genes associated with the assimilation of ethanolamine, an important nitrogen source for EHEC, was poorly induced in EHEC growing in rectum content, suggesting that ethanolamine is mainly assimilated in the cattle rumen and small intestine. Respiratory flexibility would also be required for EHEC survival because of the redundancy of dehydrogenases and reductases simultaneously induced in the bovine DCs, probably in response to the availability of electron donors and acceptors.

Conclusion

EHEC EDL933 showed a high flexibility in the activation of genes involved in respiratory pathways and assimilation of carbon and nitrogen sources, most of them from animal origin. This may allow the bacterium to adapt and survive in the various bovine GIT compartments. Obtaining a better understanding of EHEC physiology in bovine GIT is a key step to ultimately propose strategies to limit EHEC carriage and shedding by cattle.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5167-y) contains supplementary material, which is available to authorized users.

Efficacy of a recombinant Intimin, EspB and Shiga toxin 2B vaccine in calves experimentally challenged with Escherichia coli O157:H7

Escherichia coli O157:H7 is a zoonotic pathogen of global importance and the serotype of Shiga toxin-producing E.coli (STEC) most frequently associated with Hemolytic Uremic Syndrome (HUS) in humans. The main STEC reservoir is cattle. Vaccination of calves with the carboxy-terminal fraction of Intimin γ (IntC280) and EspB can reduce E.coli O157:H7 fecal shedding after experimental challenge. Shiga toxin (Stx) exerts local immunosuppressive effects in the bovine intestine and Stx2B fused to Brucella lumazine synthase (BLS-Stx2B) induces Stx2-neutralizing antibodies. To determine if an immune response against Stx could improve a vaccine's effect on fecal shedding, groups of calves were immunized with EspB + IntC280, with EspB + IntC280 + BLS-Stx2B, or kept as controls. At 24 days post vaccination calves were challenged with E.coli O157:H7. Shedding of E.coli O157:H7 was assessed in recto-anal mucosal swabs by direct plating and enrichment followed by immunomagnetic separation and multiplex PCR. Calves were euthanized 15 days after the challenge and intestinal segments were obtained to assess mucosal antibodies. Vaccination induced a significant increase of IntC280 and EspB specific antibodies in serum and intestinal mucosa in both vaccinated groups. Antibodies against Stx2B were detected in serum and intestinal mucosa of animals vaccinated with 3 antigens. Sera and intestinal homogenates were able to neutralize Stx2 verocytotoxicity compared to the control and the 2-antigens vaccinated group. Both vaccines reduced E.coli O157:H7 shedding compared to the control group. The addition of Stx2B to the vaccine formulation did not result in a superior level of protection compared to the one conferred by IntC280 and EspB alone. It remains to be determined if the inclusion of Stx2B in the vaccine alters E.coli O157:H7 shedding patterns in the long term and after recurrent low dose exposure as occurring in cattle herds.

Enterohaemorrhagic and other Shiga toxin-producing Escherichia coli (STEC): Where are we now regarding diagnostics and control strategies?

Escherichia coli comprises a highly diverse group of Gram-negative bacteria and is a common member of the intestinal microflora of humans and animals. Generally, such colonization is asymptomatic; however, some E. coli strains have evolved to become pathogenic and thus cause clinical disease in susceptible hosts. One pathotype, the Shiga toxigenic E. coli (STEC) comprising strains expressing a Shiga-like toxin is an important foodborne pathogen. A subset of STEC are the enterohaemorrhagic E. coli (EHEC), which can cause serious human disease, including haemolytic uraemic syndrome (HUS). The diagnosis of EHEC infections and the surveillance of STEC in the food chain and the environment require accurate, cost-effective and timely tests. In this review, we describe and evaluate tests now in routine use, as well as upcoming test technologies for pathogen detection, including loop-mediated isothermal amplification (LAMP) and whole-genome sequencing (WGS). We have considered the need for improved diagnostic tools in current strategies for the control and prevention of these pathogens in humans, the food chain and the environment. We conclude that although significant progress has been made, STEC still remains an important zoonotic issue worldwide. Substantial reductions in the public health burden due to this infection will require a multipronged approach, including ongoing surveillance with high-resolution diagnostic techniques currently being developed and integrated into the routine investigations of public health laboratories. However, additional research requirements may be needed before such high-resolution diagnostic tools can be used to enable the development of appropriate interventions, such as vaccines and decontamination strategies.

Analysis of whole genome sequencing for the Escherichia coli O157:H7 typing phages

Background

Shiga toxin producing Escherichia coli O157 can cause severe bloody diarrhea and haemolytic uraemic syndrome. Phage typing of E. coli O157 facilitates public health surveillance and outbreak investigations, certain phage types are more likely to occupy specific niches and are associated with specific age groups and disease severity. The aim of this study was to analyse the genome sequences of 16 (fourteen T4 and two T7) E. coli O157 typing phages and to determine the genes responsible for the subtle differences in phage type profiles.

Results

The typing phages were sequenced using paired-end Illumina sequencing at The Genome Analysis Centre and the Animal Health and Veterinary Laboratories Agency and bioinformatics programs including Velvet, Brig and Easyfig were used to analyse them. A two-way Euclidian cluster analysis highlighted the associations between groups of phage types and typing phages. The analysis showed that the T7 typing phages (9 and 10) differed by only three genes and that the T4 typing phages formed three distinct groups of similar genomic sequences: Group 1 (1, 8, 11, 12 and 15, 16), Group 2 (3, 6, 7 and 13) and Group 3 (2, 4, 5 and 14). The E. coli O157 phage typing scheme exhibited a significantly modular network linked to the genetic similarity of each group showing that these groups are specialised to infect a subset of phage types.

Conclusion

Sequencing the typing phage has enabled us to identify the variable genes within each group and to determine how this corresponds to changes in phage type.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1470-z) contains supplementary material, which is available to authorized users.

A systematic review and meta-analysis of the epidemiology of pathogenic Escherichia coli of calves and the role of calves as reservoirs for human pathogenic E. coli

Escherichia coli bacteria are the most common causes of diarrhea and septicemia in calves. Moreover, calves form a major reservoir for transmission of pathogenic E. coli to humans. Systematic reviews and meta-analyses of publications on E. coli as calf pathogens and the role of calves as reservoir have not been done so far. We reviewed studies between 1951 and 2013 reporting the presence of virulence associated factors (VAFs) in calf E. coli and extracted the following information: year(s) and country of sampling, animal number, health status, isolate number, VAF prevalence, serotypes, diagnostic methods, and biological assays. The prevalence of VAFs or E. coli pathotypes was compared between healthy and diarrheic animals and was analyzed for time courses. Together, 106 papers with 25,982 E. coli isolates from 27 countries tested for VAFs were included. F5, F17, and F41 fimbriae and heat-stable enterotoxin (ST) – VAFs of enterotoxigenic E. coli (ETEC) were significantly associated with calf diarrhea. On the contrary, ETEC VAF F4 fimbriae and heat-labile enterotoxin as well as enteropathogenic (EPEC), Shiga toxin-producing (STEC), and enterohemorrhagic E. coli (EHEC) were not associated with diarrhea. The prevalence increased overtime for ST-positive isolates, but decreased for F5- and STEC-positive isolates. Our study provides useful information about the history of scientific investigations performed in this domain so far, and helps to define etiological agents of calf disease, and to evaluate calves as reservoir hosts for human pathogenic E. coli.

Aflatoxin, fumonisin and Shiga toxin-producing Escherichia coli infections in calves and the effectiveness of Celmanax®/Dairyman's Choice™ applications to eliminate morbidity and mortality losses

Mycotoxin mixtures are associated with Shiga toxin-producing Escherichia coli (STEC) infections in mature cattle. STEC are considered commensal bacteria in mature cattle suggesting that mycotoxins provide a mechanism that converts this bacterium to an opportunistic pathogen. In this study, we assessed the mycotoxin content of hemorrhaged mucosa in dairy calves during natural disease outbreaks, compared the virulence genes of the STECs, evaluated the effect of the mucosal mycotoxins on STEC toxin expression and evaluated a Celmanax^®/Dairyman’s Choice™ application to alleviate disease. As for human infections, the OI-122 encoded nleB gene was common to STEC genotypes eliciting serious disease. Low levels of aflatoxin (1–3 ppb) and fumonisin (50–350 ppb) were detected in the hemorrhaged mucosa. Growth of the STECs with the mycotoxins altered the secreted protein concentration with a corresponding increase in cytotoxicity. Changes in intracellular calcium indicated that the mycotoxins increased enterotoxin and pore-forming toxin activity. A prebiotic/probiotic application eliminated the morbidity and mortality losses associated with the STEC infections. Our study demonstrates: the same STEC disease complex exists for immature and mature cattle; the significance of the OI-122 pathogenicity island to virulence; the significance of mycotoxins to STEC toxin activity; and, finally, provides further evidence that prebiotic/probiotic applications alleviate STEC shedding and mycotoxin/STEC interactions that lead to disease.

Immunization with a chimera consisting of the B subunit of Shiga toxin type 2 and brucella lumazine synthase confers total protection against Shiga toxins in mice

The striking feature of enterohemorrhagic Escherichia coli (EHEC) infections is the production of Shiga toxins (Stx) implicated in the development of the life-threatening hemolytic uremic syndrome. Despite the magnitude of the social impact of EHEC infections, no licensed vaccine or effective therapy is available for human use. One of the biggest challenges is to develop an effective and safe immunogen to ensure nontoxicity, as well as a strong input to the immune system to induce long-lasting, high-affinity Abs with anti-Stx-neutralizing capacity. The enzyme lumazine synthase from Brucella spp. (BLS) is a highly stable dimer of pentamers and a scaffold with enormous plasticity on which to display foreign Ags. Taking into account the advantages of BLS and the potential capacity of the B subunit of Stx2 to induce Abs that prevent Stx2 toxicity by blocking its entrance into the host cells, we engineered a new immunogen by inserting the B subunit of Stx2 at the amino termini of BLS. The resulting chimera demonstrated a strong capacity to induce a long-lasting humoral immune response in mice. The chimera induced Abs with high neutralizing capacity for Stx2 and its variants. Moreover, immunized mice were completely protected against i.v. Stx2 challenge, and weaned mice receiving an oral challenge with EHEC were completely protected by the transference of immune sera. We conclude that this novel immunogen represents a promising candidate for vaccine or Ab development with preventive or therapeutic ends, for use in hemolytic uremic syndrome-endemic areas or during future outbreaks caused by pathogenic strains of Stx-producing E. coli.

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.

Escherichia coli virulence factors

Escherichia coli was described in 1885 by a German pediatrician, Theodor Escherich, in the faeces of a child suffering diarrhoea. In 1893, a Danish veterinarian postulated that the E. coli species comprises different strains, some being pathogens, others not. Today the E. coli species is subdivided into several pathogenic strains causing different intestinal, urinary tract or internal infections and pathologies, in animal species and in humans. Since this congress topic is the interaction between E. coli and the mucosal immune system, the purpose of this manuscript is to present different classes of adhesins (fimbrial adhesins, afimbrial adhesins and outer membrane proteins), the type 3 secretion system, and some toxins (oligopeptide, AB, and RTX pore-forming toxins) produced by E. coli, that can directly interact with the epithelial cells of the intestinal, respiratory and urinary tracts.

Lysogeny with Shiga toxin 2-encoding bacteriophages represses type III secretion in enterohemorrhagic Escherichia coli

Lytic or lysogenic infections by bacteriophages drive the evolution of enteric bacteria. Enterohemorrhagic Escherichia coli (EHEC) have recently emerged as a significant zoonotic infection of humans with the main serotypes carried by ruminants. Typical EHEC strains are defined by the expression of a type III secretion (T3S) system, the production of Shiga toxins (Stx) and association with specific clinical symptoms. The genes for Stx are present on lambdoid bacteriophages integrated into the E. coli genome. Phage type (PT) 21/28 is the most prevalent strain type linked with human EHEC infections in the United Kingdom and is more likely to be associated with cattle shedding high levels of the organism than PT32 strains. In this study we have demonstrated that the majority (90%) of PT 21/28 strains contain both Stx2 and Stx2c phages, irrespective of source. This is in contrast to PT 32 strains for which only a minority of strains contain both Stx2 and 2c phages (28%). PT21/28 strains had a lower median level of T3S compared to PT32 strains and so the relationship between Stx phage lysogeny and T3S was investigated. Deletion of Stx2 phages from EHEC strains increased the level of T3S whereas lysogeny decreased T3S. This regulation was confirmed in an E. coli K12 background transduced with a marked Stx2 phage followed by measurement of a T3S reporter controlled by induced levels of the LEE-encoded regulator (Ler). The presence of an integrated Stx2 phage was shown to repress Ler induction of LEE1 and this regulation involved the CII phage regulator. This repression could be relieved by ectopic expression of a cognate CI regulator. A model is proposed in which Stx2-encoding bacteriophages regulate T3S to co-ordinate epithelial cell colonisation that is promoted by Stx and secreted effector proteins.

Many significant infectious diseases that impact human health evolve in animal hosts. Our work focuses on infections caused by strains of enterohemorrhagic Escherichia coli (EHEC) that cause bloody diarrhoea and life threatening kidney and brain damage in humans as an incidental host, while ruminants are a reservoir host. EHEC strains are infected with bacteriophages that can integrate their genetic material into the bacterial chromosome. This includes genes for the production of Shiga toxins (Stx) that are responsible for the severe pathology in humans. It has been demonstrated that certain EHEC strains are more likely to be associated with human disease and ‘supershedding’ animals. The current study has shown that these EHEC strains are more likely to contain two related Stx bacteriophages, rather than one, and that the intercalating bacteriophages take control of the bacterial type III secretion system that is essential for ruminant colonization. We propose that this regulation favours co-acquisition of other genetic regions that encode type III-secreted proteins and regulators that can overcome this control. This finding helps our understanding of EHEC strain evolution and indicates that selection of more toxic strains may be occurring in the ruminant host with important implications for human health.

O157:H7 and O104:H4 Vero/Shiga toxin-producing Escherichia coli outbreaks: respective role of cattle and humans

An enteroaggregative Verotoxin (Vtx)-producing Escherichia coli strain of serotype O104:H4 has recently been associated with an outbreak of haemolytic-uremic syndrome and bloody diarrhoea in humans mainly in Germany, but also in 14 other European countries, USA and Canada. This O104:H4 E. coli strain has often been described as an enterohaemorrhagic E. coli (EHEC), i.e. a Vtx-producing E. coli with attaching and effacing properties. Although both EHEC and the German O104:H4 E. coli strains indeed produce Vtx, they nevertheless differ in several other virulence traits, as well as in epidemiological characteristics. For instance, the primary sources and vehicles of typical EHEC infections in humans are ruminants, whereas no animal reservoir has been identified for enteroaggregative E. coli (EAggEC). The present article is introduced by a brief overview of the main characteristics of Vtx-producing E. coli and EAggEC. Thereafter, the O104:H4 E. coli outbreak is compared to typical EHEC outbreaks and the virulence factors and host specificity of EHEC and EAggEC are discussed. Finally, a renewed nomenclature of Vtx-producing E. coli is proposed to avoid more confusion in communication during future outbreaks and to replace the acronym EHEC that only refers to a clinical condition.

Verotoxin-2 activates mitogen-activated protein kinases in bovine adherent peripheral blood mononuclear cells

The effects of verotoxin (VT) on the mitogen-activated protein (MAP) kinase signalling pathways were investigated in bovine adherent peripheral blood mononuclear cells (PBMCs). VT2 stimulated a transient activation of both p38 MAP kinase and extracellular-regulated kinase (ERK) and stimulated an increase in tumour necrosis factor-α release from PBMCs. Bovine PBMCs react with very similar kinetics to human peripheral blood monocytes, despite the gross differences in disease outcome of the two species on infection with verotoxigenic Escherichia coli.

Hemolytic uremic syndrome: new developments in pathogenesis and treatment

Hemolytic uremic syndrome is defined by the characteristic triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. In children, most cases of HUS are caused by Shiga-toxin-producing bacteria, especially Escherichia coli O157:H7. Common vehicles of transmission include ground beef, unpasteurized milk, and municipal or swimming water. Shiga-toxin-associated HUS is a main cause of acute renal failure in young children. Management remains supportive as there is at present no specific therapy to ameliorate the prognosis. Immediate outcome is most often favourable but long-term renal sequelae are frequent due to nephron loss. Atypical HUS represents 5% of cases. In the past 15 years, mutations in complement regulators of the alternative pathway have been identified in almost 60% of cases, leading to excessive complement activation. The disease has a relapsing course and more than half of the patients either die or progress to end-stage renal failure. Recurrence after renal transplantation is frequent.

Mouldy feed, mycotoxins and Shiga toxin - producing Escherichia coli colonization associated with Jejunal Hemorrhage Syndrome in beef cattle

Background

Both O157 and non-O157 Shiga toxin - producing Escherichia coli (STECs) cause serious human disease outbreaks through the consumption of contaminated foods. Cattle are considered the main reservoir but it is unclear how STECs affect mature animals. Neonatal calves are the susceptible age class for STEC infections causing severe enteritis. In an earlier study, we determined that mycotoxins and STECs were part of the disease complex for dairy cattle with Jejunal Hemorrhage Syndrome (JHS). For STECs to play a role in the development of JHS, we hypothesized that STEC colonization should also be evident in beef cattle with JHS. Aggressive medical and surgical therapies are effective for JHS, but rely on early recognition of clinical signs for optimal outcomes suggesting that novel approaches must be developed for managing this disease. The main objective of this study was to confirm that mouldy feeds, mycotoxins and STEC colonization were associated with the development of JHS in beef cattle.

Results

Beef cattle developed JHS after consuming feed containing several types of mycotoxigenic fungi including Fusarium poae, F. verticillioides, F. sporotrichioides, Penicillium roqueforti and Aspergillus fumigatus. Mixtures of STECs colonized the mucosa in the hemorrhaged tissues of the cattle and no other pathogen was identified. The STECs expressed Stx1 and Stx2, but more significantly, Stxs were also present in the blood collected from the lumen of the hemorrhaged jejunum. Feed extracts containing mycotoxins were toxic to enterocytes and 0.1% of a prebiotic, Celmanax Trademark, removed the cytotoxicity in vitro. The inclusion of a prebiotic in the care program for symptomatic beef calves was associated with 69% recovery.

Conclusions

The current study confirmed that STECs and mycotoxins are part of the disease complex for JHS in beef cattle. Mycotoxigenic fungi are only relevant in that they produce the mycotoxins deposited in the feed. A prebiotic, Celmanax Trademark, acted as a mycotoxin binder in vitro and interfered with the progression of disease.

Advances in our understanding of the pathogenesis of glomerular thrombotic microangiopathy

Glomerular thrombotic microangiopathy is a hallmark feature of haemolytic uraemic syndrome, the leading cause of acute renal failure in childhood. This paper is a review of the different mechanistic pathways that lead to this histological picture in the kidney. It will focus on atypical HUS and complement dysregulation, but will also highlight some other recent advances in our understanding of this condition, including the potential role of the molecule vascular endothelial growth factor-A (VEGF-A).

Escherichia coli O157:H7 strain origin, lineage, and Shiga toxin 2 expression affect colonization of cattle

Enterohemorrhagic Escherichia coli O157:H7 has evolved into an important human pathogen with cattle as the main reservoir. The recent discovery of E. coli O157:H7-induced pathologies in challenged cattle has suggested that previously discounted bacterial virulence factors may contribute to the colonization of cattle. The objective of the present study was to examine the impact of lineage type, cytotoxin activity, and cytotoxin expression on the amount of E. coli O157:H7 colonization of cattle tissue and cells in vitro. Using selected bovine- and human-origin strains, we determined that lineage type predicted the amount of E. coli O157:H7 strain colonization: lineage I > intermediate lineages > lineage II. All E. coli O157:H7 strain colonization was dose dependent, with threshold colonization at 10(3) to 10(5) CFU and maximum colonization at 10(7) CFU. We also determined that an as-yet-unknown factor of strain origin was the most dominant predictor of the amount of strain colonization in vitro. The amount of E. coli O157:H7 colonization was also influenced by strain cytotoxin activity and the inclusion of cytotoxins from lineage I or intermediate lineage strains increased colonization of a lineage II strain. There was a higher level of expression of the Shiga toxin 1 gene (stx(1)) in human-origin strains than in bovine-origin strains. In addition, lineage I strains expressed higher levels of the Shiga toxin 2 gene (stx(2)). The present study supports a role for strain origin, lineage type, cytotoxin activity, and stx(2) expression in modulating the amount of E. coli O157:H7 colonization of cattle.

Maternally and naturally acquired antibodies to Shiga toxins in a cohort of calves shedding Shiga-toxigenic Escherichia coli

Calves become infected with Shiga toxin-producing Escherichia coli (STEC) early in life, which frequently results in long-term shedding of the zoonotic pathogen. Little is known about the animals' immunological status at the time of infection. We assessed the quantity and dynamics of maternal and acquired antibodies to Shiga toxins (Stx1 and Stx2), the principal STEC virulence factors, in a cohort of 27 calves. Fecal and serum samples were taken repeatedly from birth until the 24th week of age. Sera, milk, and colostrums of dams were also assessed. STEC shedding was confirmed by detection of stx in fecal cultures. Stx1- and Stx2-specific antibodies were quantified by Vero cell neutralization assay and further analyzed by immunoblotting. By the eighth week of age, 13 and 15 calves had at least one stx(1)-type and at least one stx(2)-type positive culture, respectively. Eleven calves had first positive cultures only past that age. Sera and colostrums of all dams and postcolostral sera of all newborn calves contained Stx1-specific antibodies. Calf serum titers decreased rapidly within the first 6 weeks of age. Only five calves showed Stx1-specific seroconversion. Maternal and acquired Stx1-specific antibodies were mainly directed against the StxA1 subunit. Sparse Stx2-specific titers were detectable in sera and colostrums of three dams and in postcolostral sera of their calves. None of the calves developed Stx2-specific seroconversion. The results indicate that under natural conditions of exposure, first STEC infections frequently coincide with an absence of maternal and acquired Stx-specific antibodies in the animals' sera.

Escherichia coli O157:H7 colonization in small domestic ruminants

Enterohaemorrhagic Escherichia coli O157:H7 was first implicated in human disease in the early 1980s, with ruminants cited as the primary reservoirs. Preliminary studies indicated cattle to be the sole source of E. coli O157:H7 outbreaks in humans; however, further epidemiological studies soon demonstrated that E. coli O157:H7 was widespread in other food sources and that a number of transmission routes existed. More recently, small domestic ruminants (sheep and goats) have emerged as important sources of E. coli O157:H7 human infection, particularly with the widespread popularity of petting farms and the increased use of sheep and goat food products, including unpasteurized cheeses. Although the colonization and persistence characteristics of E. coli O157:H7 in the bovine host have been studied intensively, this is not the case for small ruminants. Despite many similarities to the bovine host, the pathobiology of E. coli O157:H7 in small domestic ruminants does appear to differ significantly from that described in cattle. This review aims to critically review the current knowledge regarding colonization and persistence of E. coli O157:H7 in small domestic ruminants, including comparisons with the bovine host where appropriate.

Heterogeneity in enterohemorrhagicEscherichia coliO157:H7 fecal shedding in cattle is related toEscherichia coliO157:H7 colonization of the small and large intestine

In the last decade, Escherichia coli O157:H7 have emerged as important pathogens of the gastrointestinal tract of humans. Healthy cattle have been identified as the primary reservoir, however, the factors affecting heterogeneous E. coli O157:H7 fecal shedding are not fully understood. The aim of this study was to investigate the contribution of E. coli O157:H7 colonization of small and large intestinal sites to the heterogeneity of fecal shedding in cattle. There was a dose-dependant E. coli O157:H7 E318N colonization of duodenum, jejunum, ileum, cecum, ascending colon, spiral colon, descending colon, and the rectoanal junction in vitro with no difference in E. coli O157:H7 colonization of the rectoanal junction and other intestinal sites. There were 10–100 times greater E. coli O157:H7 colonization of intestinal sites from persistent shedding cattle compared with nonpersistent shedding cattle. Novel pathologies were associated with E. coli O157:H7 colonization sites in the small and large intestine. The first pathology, focal petechiae, was present throughout the intestinal tract of cattle that ceased shedding E. coli O157:H7 for 5–12 weeks or in the jejunum, ileum, cecum, and ascending colon of cattle shedding E. coli O157:H7 for 4–5 months. The second pathology, mucosal hemorrhages, was present in the same sites as the focal petechiae in cattle shedding for 5 months and these hemorrhages were in the final stages of repair. Several features of these hemorrhages support this conclusion including the brown appearance, low amount of classic E. coli O157:H7 induced A/E lesions, flattened epithelium, and blunted villi. Although mucosal hemorrhages were present in the jejunum, ileum, cecum, and ascending colon in cattle shedding for 4 months, many other pathologies were also present that were indicative of hemorrhagic enteritis as evidenced by the blood red appearance of hemorrhages, severe edema, and dark red erythema. Escherichia coli O157:H7 were associated with both pathologies suggesting it is the causative agent. The current study supports a relationship between the amount of E. coli O157:H7 colonization in intestinal sites and heterogeneous fecal shedding by cattle.

Epithelial and mesenchymal cells in the bovine colonic mucosa differ in their responsiveness to Escherichia coli Shiga toxin 1

Bovine colonic crypt cells express CD77 molecules that potentially act as receptors for Shiga toxins (Stx). The implication of this finding for the intestinal colonization of cattle by human pathogenic Stx-producing Escherichia coli (STEC) remains undefined. We used flow cytometric and real-time PCR analyses of primary cultures of colonic crypt cells to evaluate cell viability, CD77 expression, and gene transcription in the presence and absence of purified Stx1. A subset of cultured epithelial cells had Stx receptors which were located mainly intracellularly, with a perinuclear distribution, and were resistant to Stx1-induced apoptosis and Stx1 effects on chemokine expression patterns. In contrast, a population of vimentin-positive cells, i.e., mesenchymal/nonepithelial cells that had high numbers of Stx receptors on their surface, was depleted from the cultures by Stx1. In situ, CD77(+) cells were located in the lamina propria of the bovine colon by using immunofluorescence staining. A newly established vimentin-positive crypt cell line with high CD77 expression resisted the cytolethal effect of Stx1 but responded to Stx1 with a significant increase in interleukin-8 (IL-8), GRO-alpha, MCP-1, and RANTES mRNA. Combined stimulation with lipopolysaccharide and Stx1 increased IL-10 mRNA. Our results show that bovine colonic crypt cells of epithelial origin are resistant to both the cytotoxic and modulatory effects of Stx1. In contrast, some mucosal mesenchymal cells, preliminarily characterized as mucosal macrophages, are Stx1-responsive cells that may participate in the interaction of STEC with the bovine intestinal mucosa.

The CI repressors of Shiga toxin-converting prophages are involved in coinfection of Escherichia coli strains, which causes a down regulation in the production of Shiga toxin 2

Shiga toxins (Stx) are the main virulence factors associated with a form of Escherichia coli known as Shiga toxin-producing E. coli (STEC). They are encoded in temperate lambdoid phages located on the chromosome of STEC. STEC strains can carry more than one prophage. Consequently, toxin and phage production might be influenced by the presence of more than one Stx prophage on the bacterial chromosome. To examine the effect of the number of prophages on Stx production, we produced E. coli K-12 strains carrying either one Stx2 prophage or two different Stx2 prophages. We used recombinant phages in which an antibiotic resistance gene (aph, cat, or tet) was incorporated in the middle of the Shiga toxin operon. Shiga toxin was quantified by immunoassay and by cytotoxicity assay on Vero cells (50% cytotoxic dose). When two prophages were inserted in the host chromosome, Shiga toxin production and the rate of lytic cycle activation fell. The cI repressor seems to be involved in incorporation of the second prophage. Incorporation and establishment of the lysogenic state of the two prophages, which lowers toxin production, could be regulated by the CI repressors of both prophages operating in trans. Although the sequences of the cI genes of the phages studied differed, the CI protein conformation was conserved. Results indicate that the presence of more than one prophage in the host chromosome could be regarded as a mechanism to allow genetic retention in the cell, by reducing the activation of lytic cycle and hence the pathogenicity of the strains.

Molecular subtyping and genetic analysis of the enterohemolysin gene (ehxA) from Shiga toxin-producing escherichia coli and atypical enteropathogenic E. coli

Analyses of the distribution of virulence factors among different Escherichia coli pathotypes, including Shiga toxin-producing E. coli (STEC), may provide some insight into the mechanisms by which different E. coli strains cause disease and the evolution of distinct E. coli types. The aim of this study was to examine the DNA sequence of the gene for enterohemolysin, a plasmid-encoded toxin that readily causes the hemolysis of washed sheep erythrocytes, and to assess the distribution of enterohemolysin subtypes among E. coli isolates from various human and animal sources. The 2,997-bp ehxA gene was amplified from 227 (63.8%) of 356 stx- and/or eae-positive E. coli strains isolated from cattle and sheep and from 24 (96.0%) of 25 STEC strains isolated from humans with diarrheal disease. By using PCR and restriction fragment length polymorphism (RFLP) analysis of ehxA, six distinct PCR-RFLP types (A to F) were observed, with strains of subtypes A and C constituting 91.6% of all the ehxA-positive strains. Subtype A was associated mainly with ovine strains with stx only (P < 0.001), and subtype C was associated with bovine eae-positive strains (P < 0.001). Eleven ehxA alleles were fully sequenced, and the phylogenetic analysis indicated the presence of three closely related (>95.0%) ehxA sequence groups, one including eae-positive strains (subtypes B, C, E, and F) and the other two including mainly eae-negative STEC strains (subtypes A and D). In addition to being widespread among STEC strains, stx-negative, eae-positive strains (atypical enteropathogenic E. coli strains) isolated from cattle and sheep have similar ehxA subtypes and hemolytic activities.

Shiga toxin and Shiga toxin-encoding phage do not facilitate Escherichia coli O157:H7 colonization in sheep

Isogenic strains of Escherichia coli O157:H7, missing either stx(2) or the entire Stx2-encoding phage, were compared with the parent strain for their abilities to colonize sheep. The absence of the phage or of the Shiga toxin did not significantly impact the magnitude or duration of shedding of E. coli O157:H7.

Comparison of binding and effects of Escherichia coli Shiga toxin 1 on bovine and ovine granulocytes

Granulocytes play a pivotal role in the pathogenesis of Shiga toxin (Stx)-producing Escherichia coli (STEC) related diseases in humans. Granulocytes are attracted and activated by Stxs in the enteric mucosa and are believed to thereby contribute to the intestinal inflammation. Mature ruminants, the main reservoir hosts of STEC, do not develop pathological changes that can be attributed to the Stxs. To prove whether the latter phenomenon correlates with the inability of the Stxs to affect granulocytes of ruminants, we investigated the ability of Stx1 to bind to granulocytes of cattle and sheep and analysed the effects of Stx1 on viability, phagocytosis, and oxidative burst activity. Bovine granulocytes from blood and milk did not express Stx1-binding sites even after activation of the cells and also were resistant to Stx1. In contrast to bovine granulocytes, granulocytes of sheep constitutively expressed Stx1-receptors of the Gb(3)/CD77 type ex vivo and bound the recombinant B-subunit of Stx1 (rStxB1). Stx1 holotoxin induced apoptosis in ovine granulocytes after prolonged incubation (18h) but Stx1 only slightly altered the phagocytosis and oxidative burst activities. The rStxB1 had no effect on granulocytes of either species. While arguing in favour of our initial hypothesis, that granulocytes of both, cattle and sheep are not activated by Stxs, the results of our study are the first evidences for differences in the cellular distribution of Stx-receptors in species equally regarded as STEC carriers.

A comparison of enteropathogenic and enterohaemorrhagic Escherichia coli pathogenesis

This review covers enteropathogenic Escherichia coli (EPEC) and enterohaemorrhagic E. coli (EHEC) infections, focusing on differences in their virulence factors and regulation. While Shiga-toxin expression from integrated bacteriophages sets EHEC apart from EPEC, EHEC infections often originate from asymptomatic carriage in ruminants whereas human EPEC are considered to be overt pathogens and more host-restricted. In part, these differences reflect variation in adhesin repertoire, type III-secreted effectors and the way in which these factors are regulated.

Intestinal Shiga toxin-producing Escherichia coli bacteria mitigate bovine leukemia virus infection in experimentally infected sheep

Ruminants often carry gastrointestinal Shiga toxin (Stx)-producing Escherichia coli (STEC). Stxs belong to a large family of ribosome-inactivating proteins (RIPs), found in many plants and some bacteria. Plant RIPs, secreted into extracellular spaces, limit the spread of viruses through plant tissues by penetrating and killing virally infected cells. Previously, we showed Stx activity against bovine leukemia virus (BLV)-infected cells in vitro and hypothesized that STEC bacteria have antiviral activity in ruminant hosts. Here, we investigated the impact of STEC on the initial phases of BLV infection in sheep. Sheep were treated with biweekly oral doses of E. coli O157:H7 (an STEC) or an isogenic stx mutant strain. A different group of sheep were similarly treated with five naturally occurring ovine STEC isolates or stx-negative E. coli. Intestinal STEC bacteria were enumerated and identified by standard fecal culture and DNA hybridization. Oral STEC treatment did not always result in carriage of STEC, although many animals consistently presented with >10(4) CFU/g feces. BLV viremia was assessed by spontaneous lymphocyte proliferation (SLP) in cultures of blood mononuclear cells and by syncytium formation in cocultures of the same with F-81 indicator cells. SLP was lower (P < 0.05) and syncytia were fewer (P < 0.05) in STEC-treated sheep than in untreated sheep. Both lower SLP and fewer syncytia positively correlated with fecal STEC numbers. Average weight gain post-BLV challenge was higher in STEC-treated sheep than in untreated sheep (P < 0.05). These results support the hypothesis that in ruminants, intestinal STEC bacteria have antiviral activity and mitigate BLV-induced disease.

Retrograde transport pathways utilised by viruses and protein toxins

A model has been presented for retrograde transport of certain toxins and viruses from the cell surface to the ER that suggests an obligatory interaction with a glycolipid receptor at the cell surface. Here we review studies on the ER trafficking cholera toxin, Shiga and Shiga-like toxins, Pseudomonas exotoxin A and ricin, and compare the retrograde routes followed by these protein toxins to those of the ER trafficking SV40 and polyoma viruses. We conclude that there is in fact no obligatory requirement for a glycolipid receptor, nor even with a protein receptor in a lipid-rich environment. Emerging data suggests instead that there is no common pathway utilised for retrograde transport by all of these pathogens, the choice of route being determined by the particular receptor utilised.

Enterohaemorrhagic E. coli in veterinary medicine

The emergence of enterohaemorrhagic Escherichia coli (EHEC) as major human pathogens began with the identification of serotype O157:H7 in the early 1980s as the cause of various food-borne outbreaks of severe intestinal disease. The key virulence factors include verocytotoxins (Vt) and effectors and adhesins associated with type III secretion systems. Tracing the origins of human outbreaks reveals that the primary source of this organism is the ruminant gastro-intestinal tract and a variety of transmission routes to humans have been identified. The epidemiology of E. coli O157:H7 within cattle and other ruminants has been studied extensively and the prevalence of non-O157:H7 serotypes contrasts with the observed dominance of E. coli O157:H7 amongst human EHEC isolates. Although there is some evidence that EHEC cause disease in young animals, the high prevalence of Vt within healthy ruminants suggests that this is not a virulence factor within these species. An understanding of the mechanisms underpinning EHEC persistence within their natural reservoir hosts and the development of a molecular understanding of EHEC biology and evolution could eventually allow a reduction in the incidence of human disease and may reduce future threats. The use of animal models to replicate and study human EHEC pathogenesis is described.

The Shiga toxin-producing Escherichia coli, their ruminant hosts, and potential on-farm interventions: a review

The emergence of Shiga toxin-producing Escherichia coli serotype O157:H7 as a major human pathogen over the last 2 decades has focused attention on this organism’s ruminant hosts. Despite implementation of conventional control methods, people continue to become seriously ill from contaminated meat or other food products, manure-contaminated drinking and recreational water, and direct contact with ruminants. E. coli O157:H7 can cause life-threatening disease, and is a particular threat to children, through acute and chronic kidney damage. Compared with other food-borne bacteria, E. coli O157:H7 has a remarkably low infectious dose and is environmentally robust. Cattle are largely unaffected by this organism and have been identified as the major source of E. coli O157:H7 entering the human food chain. Other Shiga toxin-producing E. coli can be pathogenic to humans and there is increasing evidence that their significance has been underestimated. Governments around the world have acted to tighten food safety regulations, and to investigate animal sources and on-farm control of this and related organisms. Potential intervention strategies on-farm include: feed and water hygiene, altered feeding regimes, specific E. coli vaccines, antibacterials, antibiotics, probiotics, and biological agents or products such as bacteriophages, bacteriocins, or colicins.

Shiga toxin binding to isolated porcine tissues and peripheral blood leukocytes

Shiga toxin (Stx) binding sites in porcine tissues and leukocytes were identified by the use of Stx overlay and anti-CD77/Gb3 immunoassays. Stx1 and Stx2 bound to similar tissue locations and leukocytes, although some differences were noted. Previously unreported Stx binding sites were identified in kidney tubules, intestinal lymphoid aggregates, sinusoidal liver cells, alveolar macrophages, and peripheral blood leukocytes.

Identification of Escherichia coli O157 : H7 genes influencing colonization of the bovine gastrointestinal tract using signature-tagged mutagenesis

Enterohaemorrhagic Escherichia coli (EHEC) cause acute gastroenteritis in humans that may be complicated by life-threatening systemic sequelae. The predominant EHEC serotype affecting humans in the UK and North America is O157 : H7 and infections are frequently associated with contact with ruminant faeces. Strategies to reduce the carriage of EHEC in ruminants are expected to lower the incidence of human EHEC infections; however, the molecular mechanisms underlying persistence of EHEC in ruminants are poorly understood. This paper reports the first comprehensive survey for EHEC factors mediating colonization of the bovine intestines by using signature-tagged transposon mutagenesis. Seventy-nine E. coli O157 : H7 mutants impaired in their ability to colonize calves were isolated and 59 different genes required for intestinal colonization were identified by cloning and sequencing of the transposon insertion sites. Thirteen transposon insertions were clustered in the locus of enterocyte effacement (LEE), which encodes a type III protein secretion system required for the formation of attaching and effacing lesions on intestinal epithelia. A putative structural component of the apparatus (EscN) is essential for intestinal colonization; however, the type III secreted effector protein Map plays only a minor role. Other Type III secretion-associated genes were implicated in colonization of calves by E. coli O157 : H7, including z0990 (ecs0850), which encodes the non-LEE-encoded type III secreted effector NleD and the closely related z3023 (ecs2672) and z3026 (ecs2674) genes which encode homologues of Shigella IpaH proteins. We also identified a novel fimbrial locus required for intestinal colonization in calves by E. coli O157 : H7 (z2199-z2206; ecs2114-ecs2107/locus 8) and demonstrated that a mutant harbouring a deletion of the putative major fimbrial subunit gene is rapidly out-competed by the parent strain in co-infection studies. Our data provide valuable new information for the development of intervention strategies.

Serotypes and virulence gene profiles of shiga toxin-producing Escherichia coli strains isolated from feces of pasture-fed and lot-fed sheep

Shiga toxin-producing Escherichia coli (STEC) strains possessing genes for enterohemolysin (ehxA) and/or intimin (eae), referred to here as complex STEC (cSTEC), are more commonly recovered from the feces of humans with hemolytic uremic syndrome and hemorrhagic colitis than STEC strains that do not possess these accessory virulence genes. Ruminants, particularly cattle and sheep, are recognized reservoirs of STEC populations that may contaminate foods destined for human consumption. We isolated cSTEC strains from the feces of longitudinally sampled pasture-fed sheep, lot-fed sheep maintained on diets comprising various combinations of silage and grain, and sheep simultaneously grazing pastures with cattle to explore the diversity of cSTEC serotypes capable of colonizing healthy sheep. A total of 67 cSTEC serotypes were isolated, of which 21 (31.3%), mainly isolated from lambs, have not been reported. Of the total isolations, 58 (86.6%) were different from cSTEC serotypes isolated from a recent study of longitudinally sampled healthy Australian cattle (M. Hornitzky, B. A. Vanselow, K. Walker, K. A. Bettelheim, B. Corney, P. Gill, G. Bailey, and S. P. Djordjevic, Appl. Environ. Microbiol. 68:6439-6445, 2002). Our data suggest that cSTEC serotypes O5:H(-), O75:H8, O91:H(-), O123:H(-), and O128:H2 are well adapted to colonizing the ovine gastrointestinal tract, since they were the most prevalent serotypes isolated from both pasture-fed and lot-fed sheep. Collectively, our data show that Australian sheep are colonized by diverse cSTEC serotypes that are rarely isolated from healthy Australian cattle.

Interaction of Shiga toxin from Escherichia coli with human intestinal epithelial cell lines and explants: Stx2 induces epithelial damage in organ culture

Shiga toxins (Stx) produced by Escherichia coli are associated with systemic complications such as haemolytic-uraemic syndrome. The mechanism of Stx translocation across the epithelial barrier is unknown as human intestinal epithelium lacks receptor Gb3. In this study, we have examined the interaction of purified Stx1 and 2 with Caco-2 (Gb3+) and T84 (Gb3-) cell lines, and determined the effects of Stx on human intestine using in vitro organ culture (IVOC). Stx exposure caused inhibition of protein synthesis and apoptosis in Caco-2 but not in T84 cells. However, both Stx1 and 2 were transported to the endoplasmic reticulum, and the Stx1 A-subunit was cleaved in a furin-dependent manner in both cell lines. Thus, a Gb3-independent retrograde transport route exists in T84 cells for Stx that does not induce cell damage. IVOC demonstrated increased epithelial cell extrusion in response to exposure to Stx2, but not Stx1, in both small intestine and colon. Pretreatment of Stx2 with Stx2-specific antibody abrogated this effect. Overlaying frozen sections with Stx showed lamina propria, but not epithelial, cell binding that paralleled Gb3 localization, and included endothelium and pericryptal myofibroblasts. This indicates that human intestinal epithelium may evince Stx2-induced damage in the absence of Gb3 receptors, by an as yet unrecognized mechanism.

Phenotypic and functional characterization of intraepithelial lymphocytes in a bovine ligated intestinal loop model of enterohaemorrhagic Escherichia coli infection

Ruminants are a major reservoir of enterohaemorrhagic Escherichia coli (EHEC), which cause acute gastroenteritis in humans with potentially life-threatening sequelae. The mechanisms underlying EHEC persistence in ruminant hosts are poorly understood. EHEC produce several cytotoxins that inhibit the proliferation of bovine lymphocytes in vitro and influence EHEC persistence in calves, suggesting that bacterial suppression of mucosal inflammation may be important in vivo. In order to address this hypothesis, intraepithelial lymphocytes (IEL) obtained from ligated intestinal loops of five 9-14 day old calves were characterized 12 h after inoculation with E. coli strains. Loops were inoculated with an EHEC O103 : H2 strain, an isogenic Deltastx1 mutant incapable of producing Shiga toxin 1 (Stx1) and a porcine non-pathogenic E. coli strain. The IEL mainly comprised activated CD2(+) CD3(+) CD6(+) CD8alpha(+) T cells and resembled IEL obtained from the intestinal mucosa of orally challenged calves. Forty per cent of all IEL were potentially sensitive to Stx1 in that they expressed the receptor for Stx1. Nevertheless, analysis of IEL from inoculated loops failed to detect a significant effect of the different E. coli strains on proliferative capacity, natural killer cell activity or the cytokine mRNA profile. However, the EHEC wild-type strain reduced the percentage of CD8alpha(+) T cells in the ileal mucosa compared with loops inoculated with the Deltastx1 mutant. This shift in IEL composition was not associated with inhibition of IEL proliferation in situ, since the majority of the IEL from all loops were in the G(0)/G(1) phase of the cell cycle. These studies indicate that the ligated ileal loop model will be a useful tool to dissect the mechanisms underlying suppression of mucosal inflammation by EHEC in the reservoir host.

Bovine ileal intraepithelial lymphocytes represent target cells for Shiga toxin 1 from Escherichia coli

The discovery that bovine peripheral lymphocytes are sensitive to Stx1 identified a possible mechanism for the persistence of infections with Shiga toxin (Stx)-producing Escherichia coli (STEC) in the bovine reservoir host. If intraepithelial lymphocytes (IEL) are also sensitive to Stx1, the idea that Stx1 affects inflammation in the bovine intestine is highly attractive. To prove this hypothesis, ileal IEL (iIEL) were prepared from adult cattle, characterized by flow cytometry, and subjected to functional assays in the presence and absence of purified Stx1. We found that 14.9% of all iIEL expressed Gb(3)/CD77, the Stx1 receptor on bovine lymphocytes, and 7.9% were able to bind the recombinant B subunit of Stx1. The majority of Gb(3)/CD77(+) cells were activated CD3(+) CD6(+) CD8 alpha(+) T cells, whereas only some CD4(+) T cells and B cells expressed Gb(3)/CD77. However, Stx1 blocked the mitogen-induced transformation to enlarged blast cells within all subpopulations to a similar extent and significantly reduced the percentage of Gb(3)/CD77(+) cells. Although Stx1 did not affect the natural killer cell activity of iIEL, the toxin accelerated the synthesis of interleukin-4 (IL-4) mRNA and reduced the amount of IL-8 mRNA in bovine iIEL cultures. Because the intestinal system comprises a rich network of interactions between different types of cells and any dysfunction may influence the course of intestinal infections, this demonstration that Stx1 can target bovine IEL may be highly relevant for our understanding of the interplay between STEC and its reservoir host.

Non-toxigenic Escherichia coli O157:H7 strain NCTC12900 causes attaching-effacing lesions and eae-dependent persistence in weaned sheep

Ruminants are regarded as a primary reservoir for Escherichia coli O157:H7, an important human pathogen. Intimin, encoded by the Locus of Enterocyte Effacement by E. coli O157:H7 organisms, has been cited as one bacterial mechanism of colonisation of the gastrointestinal tract. To confirm this and to test whether a non-toxigenic E. coli O157:H7 strain would colonise and persist in a sheep model, E. coli O157:H7 strain NCTC12900, that lacks Shiga toxin (stx) genes, was evaluated for use in a sheep model of persistence. Following oral inoculation of six-week-old sheep, persistent excretion of NCTC12900 was observed for up to 48 days. E. coli O157-associated attaching-effacing (AE) lesions were detected in the caecum and rectum of one six-week-old lamb, one day after inoculation. This is the first recorded observation of AE lesions in orally inoculated weaned sheep. Also, mean faecal excretion scores of NCTC12900 and an isogenic intimin (eae)-deficient mutant were determined from twenty-four six-week-old orally inoculated sheep. The eae mutant was cleared within 20 days and had lower mean excretion scores at all time points after day one post inoculation compared with the parental strain that was still being excreted at 48 days. Tissues were collected post mortem from animals selected at random from the study groups over the time course of the experiment. The eae mutant was detected in only 1/43 samples but the parental strain was recovered from 64/140 samples primarily from the large bowel although rumen, duodenum, jejunum, and ileum were culture positive especially from animals that were still excreting at and beyond 27 days after inoculation.

stx1c Is the most common Shiga toxin 1 subtype among Shiga toxin-producing Escherichia coli isolates from sheep but not among isolates from cattle

Unlike Shiga toxin 2 (stx(2)) genes, most nucleotide sequences of Shiga toxin 1 (stx(1)) genes from Shiga toxin-producing Escherichia coli (STEC), Shigella dysenteriae, and several bacteriophages (H19B, 933J, and H30) are highly conserved. Consequently, there has been little incentive to investigate variants of stx(1) among STEC isolates derived from human or animal sources. However stx(1OX3), originally identified in an OX3:H8 isolate from a healthy sheep in Germany, differs from other stx(1) subtypes by 43 nucleotides, resulting in changes to 12 amino acid residues, and has been renamed stx(1c). In this study we describe the development of a PCR-restriction fragment length polymorphism (RFLP) assay that distinguishes stx(1c) from other stx(1) subtypes. The PCR-RFLP assay was used to study 378 stx(1)-containing STEC isolates. Of these, 207 were isolated from sheep, 104 from cattle, 45 from humans, 11 from meat, 5 from swine, 5 from unknown sources, and 1 from a cattle water trough. Three hundred fifty-five of the 378 isolates (93.9%) also possessed at least one other associated virulence gene (ehxA, eaeA, and/or stx(2)); the combination stx(1), stx(2), and ehxA was the most common (175 of 355 [49.3%]), and 90 of 355 (25.4%) isolates possessed eaeA. One hundred thirty-six of 207 (65.7%) ovine isolates possessed stx(1c) alone and belonged to 41 serotypes. Seventy-one of 136 (52.2%) comprised the common ovine serotypes O5:H(-), O128:H2, and O123:H(-). Fifty-two of 207 isolates (25.1%) possessed an stx(1) subtype; 27 (51.9%) of these belonged to serotype O91:H(-). Nineteen of 207 isolates (9.2%) contained both stx(1c) and stx(1) subtypes, and 14 belonged to serotype O75:H8. In marked contrast, 97 of 104 (93.3%) bovine isolates comprising 44 serotypes possessed an stx(1) subtype, 6 isolates possessed stx(1c), and the remaining isolate possessed both stx(1c) and stx(1) subtypes. Ten of 11 (91%) isolates cultured from meat in New Zealand possessed stx(1c) (serotypes O5:H(-), O75:H8/H40, O81:H26, O88:H25, O104:H(-)/H7, O123:H(-)/H10, and O128:H2); most of these serotypes are commonly recovered from the feces of healthy sheep. Serotypes containing stx(1) recovered from cattle rarely were the same as those isolated from sheep. Although an stx(1c) subtype was never associated with the typical enterohemorrhagic E. coli serogroups O26, O103, O111, O113, and O157, 13 human isolates possessed stx(1c). Of these, six isolates with serotype O128:H2 (from patients with diarrhea), four O5:H(-) isolates (from patients with hemolytic-uremic syndrome), and three isolates with serotypes O123:H(-) (diarrhea), OX3:H8 (hemolytic-uremic syndrome), and O81:H6 (unknown health status) represent serotypes that are commonly isolated from sheep.

Verotoxin 1 binding to intestinal crypt epithelial cells results in localization to lysosomes and abrogation of toxicity

Verotoxins (VTs) are important virulence factors of enterohaemorrhagic Escherichia coli (EHEC), a group of bacteria associated with severe disease sequelae in humans. The potent cytotoxic activity of VTs is important in pathogenicity, resulting in the death of cells expressing receptor Gb3 (globotriaosylceramide). EHEC, particularly serotype O157:H7, frequently colonize reservoir hosts (such as cattle) in the absence of disease, however, the basis to avirulence in this host has been unclear. The objective of this study was assessment of interaction between VT and intestinal epithelium, which represents the major interface between the host and enteric organisms. Bovine intestinal epithelial cells expressed Gb3 in vitro in primary cell cultures, localizing specifically to proliferating crypt cells in corroboration with in situ immunohistological observations on intestinal mucosa. Expression of receptor by these cells contrasts with the absence of Gb3 on human intestinal epithelium in vivo. Despite receptor expression, VT exhibited no cytotoxic activity against bovine epithelial cells. Sub-cellular localization of VT indicated that this toxin was excluded from endoplasmic reticulum but localized to lysosomes, corresponding with abrogation of cytotoxicity. VT intracellular trafficking was unaffected by treatment of primary cell cultures with methyl-beta-cyclodextrin, indicating that Gb3 in these cells is not associated with lipid rafts but is randomly distributed in the membrane. The combination of Gb3 isoform, membrane distribution and VT trafficking correlate with observations of other receptor-positive cells that resist verocytotoxicity. These studies demonstrate that intestinal epithelium is an important determinant in VT interaction with major implications for the differential consequences of EHEC infection in reservoir hosts and humans.

Antiviral activity of shiga toxin requires enzymatic activity and is associated with increased permeability of the target cells

This study expanded our earlier finding that Shiga toxin type 1 (Stx1) has activity against bovine leukemia virus (BLV) (W. A. Ferens and C. J. Hovde, Infect. Immun. 68:4462-4469, 2000). The Stx molecular motifs required for antiviral activity were identified, and a mechanism of Stx action on virally infected cells is suggested. Using inhibition of BLV-dependent spontaneous lymphocyte proliferation as a measure of antiviral activity, we showed that Stx2 had antiviral activity similar to that of Stx1. Enzymatic and antiviral activities of three StxA1 chain mutants deficient in enzymatic activity or aspects of receptor-mediated cytotoxicity were compared. Using protein synthesis inhibition to measure enzymatic activity, the mutant E167D was 300-fold less catalytically active than wild-type StxA1, was minimally active in antiviral assays, and did not inhibit synthesis of viral proteins. Two StxA1 mutants, A231D-G234E and StxA(1)1 (enzymatically active but unable to kill cells via the classical receptor-mediated route), had undiminished antiviral activity. Although binding of radiolabeled StxA1 to bovine blood cells or to free virus was not detected, flow cytometric analysis showed that the number of BLV-expressing cells were specifically reduced in cultures treated with Stx. These unique and rare lymphocytes were highly permeable to 40- and 70-kDa fluorescent dextrans, indicating that direct absorption of toxins by virus-expressing cells is a potential mechanism of target cell intoxication. These results support the hypothesis that Stx-producing Escherichia coli colonization of the gastrointestinal tract may benefit ruminant hosts by the ability of Stxs to exert antiviral activity.