Effect of Shiga toxin and Shiga-like toxins on eukaryotic cells

Detection of pathogenic, heteropathogenic and hybrid Escherichia coli strains in psittacines from zoos and breeders in the state of Ceará, Brazil

The current study aimed to detect virulence, hetero-pathogenicity, and hybridization genes in Escherichia coli strains, previously isolated from cloacal swabs in commercial breeding psittacines and zoological collections, via multiplex PCR. A total of 68 strains of E. coli, previously isolated from psittacines in zoos and commercial breeding facilities in Ceará, Brazil, were assessed for the presence of the following genes and/or probes: eae, bfpA (EPEC - Enteropathogenic E. coli), CVD432 (EAEC - Enteroaggregative E. coli); LT gene and ST gene (ETEC - Enterotoxigenic E. coli); ipaH (EIEC - Enteroinvasive E. coli); stx1 and stx2 (STEC - Shiga toxin-producing E. coli); iroN, ompT, hlyF, iss, and iutA (APEC - Avian pathogenic E. coli). Of the 68 E. coli strains analyzed, 61 (98.7 %) were positive for the following genes and/or probes: Stx1 (61/98.7 %), ST gene (54/79.4 %), CVD432 (49/72 %), bfpA (44/64.7 %), eae (42/61.8 %), Stx2 (41/60.3 %), ipaH (34/50 %), LT gene (33/48.5 %), iroN (21/30.9 %), hlyF (11/6.2 %), iss (06/8.8 %) and iutA (06/8.8 %). The following diarrheagenic pathotypes were identified: 66 (97 %) from STEC, 49 (72 %) from EAEC, 35 (52 %) from EIEC, 25 (37 %) from ETEC, and one (1.5 %) from EPEC. Regarding hetero-pathogenicity, 50 (74 %) heterogeneous strains were identified. Positivity for APEC was seen in four (6 %) strains, all characterized as pathogenic hybrids. This study describes significant associations of virulence factors in E. coli strains DEC/DEC and DEC/APEC, which were isolated from psittacines and may be potentially harmful to One Health.

Shiga toxin down-regulates ERG protein in endothelial cells and impairs angiogenesis

BACKGROUND

Shiga toxin (Stx) can activate inflammatory signaling, leading to vascular dysfunction and promotion of a pro-thrombotic tissue microenvironment. Stx can trigger the development of the enterohemorrhagic (childhood) hemolytic uremic syndrome (eHUS), a triad of thrombocytopenia, hemolytic anemia, and acute kidney injury, often requiring dialysis. Additional features may include damage to other organs, including the gastrointestinal tract, pancreas, brain and cardiovascular system; death occurs in 2-5 %. eHUS is a thrombotic microangiopathy; thus, endothelial cell (EC) injury and platelet fibrin thrombus formation in glomerular arterioles and in the arterioles of other affected organs are likely. To elucidate mechanisms of this microangiopathy, we examined in human ECs the regulation of the platelet adhesion proteins P-selectin and von Willebrand factor (VWF), along with the downregulation of erythroblast-transformation-specific transcription factor (ERG) a key regulator of angiogenesis and megakaryocyte development.

METHODS

VWF, P-selectin, and ERG levels were determined using immunofluorescence and Western blot in human umbilical endothelial cells (HUVECs). HUVECs were treated with tumor necrosis factor-alpha (TNF-α), Stx-1 or both, versus normal controls. Capillary morphogenesis on Matrigel was performed using HUVECs treated, for 22 h with TNF-α, Stx-1, or both, or treated 4 h with Stx-1 alone or in combination with TNF-α for 22 h.

RESULTS

Stx-1 significantly reduced ERG and VWF expression on HUVECs, but upregulated P-selectin expression. ERG levels decreased with Stx-1 alone or in combination with TNF-α, in the nuclear, perinuclear and cytoplasmatic regions. Stx-1 reduced capillary morphogenesis, while Stx-1-TNF-α combined treatment reduced capillary morphogenesis still further.

CONCLUSIONS

In the presence of Stx-1 or TNF-α or both treatments, ECs were activated, expressing higher levels of P-selectin and lower levels of VWF. Our findings, further, provide evidence that Stx-1 downregulates ERG, repressing angiogenesis in vitro.

A Novel EGFR Targeted Immunotoxin Based on Cetuximab and Type 1 RIP Quinoin Overcomes the Cetuximab Resistance in Colorectal Cancer Cells

Cetuximab is a monoclonal antibody blocking the epidermal growth factor receptor (EGFR) in metastatic colorectal cancer (mCRC). However, cetuximab treatment has no clinical benefits in patients affected by mCRC with KRAS mutation or in the presence of constitutive activation of signalling pathways acting downstream of the EGFR. The aim of this study was to improve cetuximab's therapeutic action by conjugating cetuximab with the type 1 ribosome inactivating protein (RIP) quinoin isolated from quinoa seeds. A chemical conjugation strategy based on the use of heterobifunctional reagent succinimidyl 3-(2-pyridyldithio)propionate (SPDP) was applied to obtain the antibody-type 1 RIP chimeric immunoconjugate. The immunotoxin was then purified by chromatographic technique, and its enzymatic action was evaluated compared to quinoin alone. Functional assays were performed to test the cytotoxic action of the quinoin cetuximab immunoconjugate against the cetuximab-resistant GEO-CR cells. The novel quinoin cetuximab immunoconjugate showed a significant dose-dependent cytotoxicity towards GEO-CR cells, achieving IC50 values of 27.7 nM (~5.0 μg/mL) at 72 h compared to cetuximab (IC50 = 176.7 nM) or quinoin (IC50 = 149.3 nM) alone assayed in equimolar amounts. These results support the therapeutic potential of quinoin cetuximab immunoconjugate for the EGFR targeted therapy, providing a promising candidate for further development towards clinical use in the treatment of cetuximab-resistant metastatic colorectal cancer.

Novel lectin-based chimeric antigen receptors target Gb3-positive tumour cells

The link between cancer and aberrant glycosylation has recently become evident. Glycans and their altered forms, known as tumour-associated carbohydrate antigens (TACAs), are diverse, complex and difficult to target therapeutically. Lectins are naturally occurring glycan-binding proteins  that offer a unique opportunity to recognise TACAs. T cells expressing chimeric antigen receptors (CARs) have proven to be a successful immunotherapy against leukaemias, but so far have shown limited success in solid tumours. We developed a panel of lectin-CARs that recognise the glycosphingolipid globotriaosylceramide (Gb3), which is overexpressed in various cancers, such as Burkitt's lymphoma, colorectal, breast and pancreatic. We have selected the following lectins: Shiga toxin's B-subunit from Shigella dysenteriae, LecA from Pseudomonas aeruginosa, and the engineered lectin Mitsuba from Mytilus galloprovincialis as antigen-binding domains and fused them to a well-known second-generation CAR. The Gb3-binding lectin-CARs have demonstrated target-specific cytotoxicity against Burkitt's lymphoma-derived cell lines as well as solid tumour cells from colorectal and triple-negative breast cancer. Our findings reveal the big potential of lectin-based CARs as therapeutical applications to target Gb3 and other TACAs expressed in haematological malignancies and solid tumours.

Characterization of Lung Injury following Abrin Pulmonary Intoxication in Mice: Comparison to Ricin Poisoning

Abrin is a highly toxic protein obtained from the seeds of the rosary pea plant Abrus precatorius, and it is closely related to ricin in terms of its structure and chemical properties. Both toxins inhibit ribosomal function, halt protein synthesis and lead to cellular death. The major clinical manifestations following pulmonary exposure to these toxins consist of severe lung inflammation and consequent respiratory insufficiency. Despite the high similarity between abrin and ricin in terms of disease progression, the ability to protect mice against these toxins by postexposure antibody-mediated treatment differs significantly, with a markedly higher level of protection achieved against abrin intoxication. In this study, we conducted an in-depth comparison between the kinetics of in vivo abrin and ricin intoxication in a murine model. The data demonstrated differential binding of abrin and ricin to the parenchymal cells of the lungs. Accordingly, toxin-mediated injury to the nonhematopoietic compartment was shown to be markedly lower in the case of abrin intoxication. Thus, profiling of alveolar epithelial cells demonstrated that although toxin-induced damage was restricted to alveolar epithelial type II cells following abrin intoxication, as previously reported for ricin, it was less pronounced. Furthermore, unlike following ricin intoxication, no direct damage was detected in the lung endothelial cell population following abrin exposure. Reduced impairment of intercellular junction molecules following abrin intoxication was detected as well. In contrast, similar damage to the endothelial surface glycocalyx layer was observed for the two toxins. We assume that the reduced damage to the lung stroma, which maintains a higher level of tissue integrity following pulmonary exposure to abrin compared to ricin, contributes to the high efficiency of the anti-abrin antibody treatment at late time points after exposure.

Isolation, Characterization and Biological Action of Type-1 Ribosome-Inactivating Proteins from Tissues of Salsola soda L

Ribosome-inactivating proteins (RIPs) are known as RNA N-glycosylases. They depurinate the major rRNA, damaging ribosomes and inhibiting protein synthesis. Here, new single-chain (type-1) RIPs named sodins were isolated from the seeds (five proteins), edible leaves (one protein) and roots (one protein) of Salsola soda L. Sodins are able to release Endo's fragment when incubated with rabbit and yeast ribosomes and inhibit protein synthesis in cell-free systems (IC₅₀ = 4.83-79.31 pM). In addition, sodin 5, the major form isolated from seeds, as well as sodin eL and sodin R, isolated from edible leaves and roots, respectively, display polynucleotide:adenosine glycosylase activity and are cytotoxic towards the Hela and COLO 320 cell lines (IC₅₀ = 0.41-1200 nM), inducing apoptosis. The further characterization of sodin 5 reveals that this enzyme shows a secondary structure similar to other type-1 RIPs and a higher melting temperature (Tm = 76.03 ± 0.30 °C) and is non-glycosylated, as other sodins are. Finally, we proved that sodin 5 possesses antifungal activity against Penicillium digitatum.

Ribotoxic Proteins, Known as Inhibitors of Protein Synthesis, from Mushrooms and Other Fungi According to Endo's Fragment Detection

rRNA N-glycosylases (EC 3.2.2.22) remove a specific adenine (A₄₃₂₄, rat 28S rRNA) in the sarcin ricin loop (SRL) involved into ribosome interaction with elongation factors, causing the inhibition of translation, for which they are known as plant 'ribosome inactivating proteins' (RIPs). However, protein synthesis inactivation could be the result of other enzymes, which often have rRNA as the target. In this scenario, Endo's assay is the most used method to detect the enzymes that are able to hydrolyze a phosphodiester bond or cleave a single N-glycosidic bond (rRNA N-glycosylases). Indeed, the detection of a diagnostic fragment from rRNA after enzymatic action, with or without acid aniline, allows one to discriminate between the N-glycosylases or hydrolases, which release the β-fragment after acid aniline treatment or α-fragment without acid aniline treatment, respectively. This assay is of great importance in the mushroom kingdom, considering the presence of enzymes that are able to hydrolyze phosphodiester bonds (e.g., ribonucleases, ribotoxins and ribotoxin-like proteins) or to remove a specific adenine (rRNA N-glycosylases). Thus, here we used the β-fragment experimentally detected by Endo's assay as a hallmark to revise the literature available on enzymes from mushrooms and other fungi, whose action consists of protein biosynthesis inhibition.

Evolution-proof inhibitors of public good cooperation: a screening strategy inspired by social evolution theory

Interference with public good cooperation provides a promising novel antimicrobial strategy since social evolution theory predicts that resistant mutants will be counter-selected if they share the public benefits of their resistance with sensitive cells in the population. Although this hypothesis is supported by a limited number of pioneering studies, an extensive body of more fundamental work on social evolution describes a multitude of mechanisms and conditions that can stabilize public behaviour, thus potentially allowing resistant mutants to thrive. In this paper we theorize on how these different mechanisms can influence the evolution of resistance against public good inhibitors. Based hereon, we propose an innovative 5-step screening strategy to identify novel evolution-proof public good inhibitors, which involves a systematic evaluation of the exploitability of public goods under the most relevant experimental conditions, as well as a careful assessment of the most optimal way to interfere with their action. Overall, this opinion paper is aimed to contribute to long-term solutions to fight bacterial infections.

Evaluation of the Anti-Shigellosis Activity of Dietary Isothiocyanates in Galleria mellonella Larvae

Cruciferous vegetables, widely present in daily diets, are a rich source of organosulfur compounds with proven health benefits, especially chemopreventive or antioxidative effects. Isothiocyanate derivatives (ITCs) exhibit a broad spectrum of biological and pharmacological activity and recently, their antibacterial properties have been of particular importance. Here, we have focused on the anti-shigellosis activity of sulforaphane (SFN) and phenethyl ITC (PEITC). The genus Shigella causes gastroenteritis in humans, which constitutes a threat to public health. Production of a potent Stx toxin by S. dysenteriae type 1 results not only in more severe symptoms but also in serious sequela, including the hemolytic uremic syndrome. Here, we present evidence that two aliphatic and aromatic ITCs derivatives, SFN and PEITC, have an effective antibacterial potency against S. dysenteriae, also negatively regulating the stx gene expression. The molecular mechanism of this effect involves induction of the global stress-induced stringent response. ITCs also inhibit bacterial virulence against the Vero and HeLa cells. We present evidence for the therapeutic effect of sulforaphane and phenethyl ITC against a S. dysenteriae infection in the Galleria mellonella larvae model. Thus, our results indicate that isothiocyanates can be effectively used to combat dangerous bacterial infections.

Structural Diversities of Lectins Binding to the Glycosphingolipid Gb3

Glycolipids are present on the surfaces of all living cells and thereby represent targets for many protein receptors, such as lectins. Understanding the interactions between lectins and glycolipids is essential for investigating the functions of lectins and the dynamics of glycolipids in living membranes. This review focuses on lectins binding to the glycosphingolipid globotriaosylceramide (Gb3), an attractive host cell receptor, particularly for pathogens and pathogenic products. Shiga toxin (Stx), from Shigella dysenteriae or Escherichia coli, which is one of the most virulent bacterial toxins, binds and clusters Gb3, leading to local negative membrane curvature and the formation of tubular plasma membrane invaginations as the initial step for clathrin-independent endocytosis. After internalization, it is embracing the retrograde transport pathway. In comparison, the homotetrameric lectin LecA from Pseudomonas aeruginosa can also bind to Gb3, triggering the so-called lipid zipper mechanism, which results in membrane engulfment of the bacterium as an important step for its cellular uptake. Notably, both lectins bind to Gb3 but induce distinct plasma membrane domains and exploit mainly different transport pathways. Not only, several other Gb3-binding lectins have been described from bacterial origins, such as the adhesins SadP (from Streptococcus suis) and PapG (from E. coli), but also from animal, fungal, or plant origins. The variety of amino acid sequences and folds demonstrates the structural versatilities of Gb3-binding lectins and asks the question of the evolution of specificity and carbohydrate recognition in different kingdoms of life.

Enteropathogenic Infections: Organoids Go Bacterial

Enteric infections represent a major health care challenge which is particularly prevalent in countries with restricted access to clean water and sanitation and lacking personal hygiene precautions, altogether facilitating fecal-oral transmission of a heterogeneous spectrum of enteropathogenic microorganisms. Among these, bacterial species are responsible for a considerable proportion of illnesses, hospitalizations, and fatal cases, all of which have been continuously contributing to ignite researchers' interest in further exploring their individual pathogenicity. Beyond the universally accepted animal models, intestinal organoids are increasingly valued for their ability to mimic key architectural and physiologic features of the native intestinal mucosa. As a consequence, they are regarded as the most versatile and naturalistic in vitro model of the gut, allowing monitoring of adherence, invasion, intracellular trafficking, and propagation as well as repurposing components of the host cell equipment. At the same time, infected intestinal organoids allow close characterization of the host epithelium's immune response to enteropathogens. In this review, (i) we provide a profound update on intestinal organoid-based tissue engineering, (ii) we report the latest pathophysiological findings defining the infected intestinal organoids, and (iii) we discuss the advantages and limitations of this in vitro model.

Aislamiento de Escherichia coli productora de toxina Shiga (STEC) en heces de ganado y detección de factores de virulencia asociados con su patogénesis

Objetivo: Aislar STEC en las heces del ganado bovino en el municipio de Ulloa, Valle del Cauca y detectar factores de virulencia asociados con la patogénesis. Materiales y métodos: Se tomaron 21 muestras provenientes de bovinos, las cuales fueron tomadas directamente del recto del animal mediante hisopos. Las muestras se procesaron hasta obtener colonias puras a las cuales se les evaluó la presencia de los genes stx1, stx2, eae, saa y hlyA mediante PCR y posteriormente, se evaluó el efecto citotóxico de las muestras positivas sobre células Vero (ATCC-CCL-81.4). Resultados: De las 21 muestras de heces de bovinos,12 presentaron bacterias con uno o ambos genes stx. Se obtuvieron 106 aislamientos totales de STEC y se observaron diferencias en cuanto a la presencia y ausencia de los genes de virulencia evaluados en los aislamientos de cada bovino, obteniendo cinco combinaciones de genes. 48 aislamientos presentaron únicamente el gen stx2 y 58 presentaron tanto el gen stx1 como el gen stx2; de los 106 aislamientos, se detectaron 44 con el gen hlyA y 57 con el gen saa. Conclusiones: Todos los sobrenadantes de STEC analizados mostraron actividad citotóxica sobre las células Vero, mientras que en ausencia de STEC las células formaron monocapa después de 48 h de incubación. Este trabajo es el primer reporte en Colombia que aporta información sobre la presencia de STEC en el ganado bovino, la presencia de factores de virulencia y el potencial efecto citotóxico que poseen estas cepas nativas.

Impact of insertion sequences on convergent evolution of Shigella species

Shigella species are specialised lineages of Escherichia coli that have converged to become human-adapted and cause dysentery by invading human gut epithelial cells. Most studies of Shigella evolution have been restricted to comparisons of single representatives of each species; and population genomic studies of individual Shigella species have focused on genomic variation caused by single nucleotide variants and ignored the contribution of insertion sequences (IS) which are highly prevalent in Shigella genomes. Here, we investigate the distribution and evolutionary dynamics of IS within populations of Shigella dysenteriae Sd1, Shigella sonnei and Shigella flexneri. We find that five IS (IS1, IS2, IS4, IS600 and IS911) have undergone expansion in all Shigella species, creating substantial strain-to-strain variation within each population and contributing to convergent patterns of functional gene loss within and between species. We find that IS expansion and genome degradation are most advanced in S. dysenteriae and least advanced in S. sonnei; and using genome-scale models of metabolism we show that Shigella species display convergent loss of core E. coli metabolic capabilities, with S. sonnei and S. flexneri following a similar trajectory of metabolic streamlining to that of S. dysenteriae. This study highlights the importance of IS to the evolution of Shigella and provides a framework for the investigation of IS dynamics and metabolic reduction in other bacterial species.

An Overview of the Elusive Passenger in the Gastrointestinal Tract of Cattle: The Shiga Toxin Producing Escherichia coli

For approximately 10,000 years, cattle have been our major source of meat and dairy. However, cattle are also a major reservoir for dangerous foodborne pathogens that belong to the Shiga toxin-producing Escherichia coli (STEC) group. Even though STEC infections in humans are rare, they are often lethal, as treatment options are limited. In cattle, STEC infections are typically asymptomatic and STEC is able to survive and persist in the cattle GIT by escaping the immune defenses of the host. Interactions with members of the native gut microbiota can favor or inhibit its persistence in cattle, but research in this direction is still in its infancy. Diet, temperature and season but also industrialized animal husbandry practices have a profound effect on STEC prevalence and the native gut microbiota composition. Thus, exploring the native cattle gut microbiota in depth, its interactions with STEC and the factors that affect them could offer viable solutions against STEC carriage in cattle.

Synthesis, physical characterization, and antifungal and antibacterial activities of oleic acid capped nanomagnetite and cobalt-doped nanomagnetite

Nanoparticles, 10–14 nm, consisting of either Fe3O4 or Co0.2Fe2.8O4 stabilized with oleic acid, were prepared using solution combustion. Their structural and magnetic properties were examined using X-ray diffractometry, scanning electron microscopy, vibrating sample magnetometry, and Fourier-transform infrared spectroscopy. The properties of both sets of materials are similar, except that the cobalt-doped particles are considerably less magnetic. The in vitro inhibitory activities of the nanoparticles were assessed against pathogenic bacteria Shigella dysenteriae, Klebsiella pneumoniae, Acinetobacter baumannii, Streptococcus pyogenes, and pathogenic fungi and molds Candida albicans, Fusarium oxysporum, and Aspergillus fumigatus. The magnetite nanoparticles were moderately effective against all tested pathogens, but the activity of the cobalt-doped nanoparticles was significantly lower, possibly due to an interruption of the Fenton reaction at the bacterial membrane. This work suggests that potentially doping magnetite with stronger metal oxidants may instead enhance their antimicrobial effects.

Effect of drying on oxidation of membrane lipids and expression of genes encoded by the Shiga toxin prophage in Escherichia coli

Drying processes do not eliminate pathogenic Escherichia coli in foods but induce sublethal injury, which may also induce the Shiga toxin (Stx) prophage. This study investigated the effect of drying on membrane lipid oxidation and stx expression in E. coli. Lipid peroxidation was probed with C₁₁-BODIPY^581/591; and stx expression was assayed by quantification of GFP in E. coli O104:H4 Δstx2a:gfp:amp^r. Treatment of E. coli with H₂O₂ oxidized the probe; probe oxidation was also observed after drying and rehydration. Lipid oxidation and the lethality of drying were reduced when cells were dried with trehalose under anaerobic condition; in addition, viability and probe oxidation differed between E. coli AW1.7 and E. coli AW1.7Δcfa. Desiccation tolerance thus relates to membrane lipid oxidation. Drying also resulted in expression of GFP in 5% of the population. Overexpression of gfp and recA after drying and rehydration suggested that the expression of Stx prophage was regulated by the SOS response. Overall, C₁₁-BODIPY^581/591 allowed investigation of lipid peroxidation in bacteria. Drying causes lipid oxidation, DNA damage and induction of genes encoded by the Stx prophage in E. coli.

Research and molecular characteristic of Shiga toxin-producing Escherichia coli isolated from sheep carcasses

Domestic ruminants are regarded as the major reservoir of Shiga toxin-producing Escherichia coli (STEC) closely related to human infection. A total of 363 ovine carcasses were swabbed in an Algiers city slaughterhouse for research on STEC. First of all, screening of the STECs was carried out by a multiplex PCR searching for the genes coding for the virulence factors stx₁ , stx₂ and eae. This step was followed by STEC isolation and serotyping. The presence of stx⁺ /stx⁺ eae⁺ genes was shown in 116 sheep carcasses (31·95%). From the 116 positive samples, 20 bacterial strains (17·24%) were isolated. Nineteen strains belonged to the species E. coli (STEC), and 1 belonged to Citrobacter braakii (eae⁺ stx₁ ⁺ ). During this study, the presence of potentially pathogenic STEC for humans on the surface of sheep carcasses was confirmed. Corrective measures should be considered at the slaughterhouse level to avoid outbreaks of STEC in Algeria. SIGNIFICANCE AND IMPACT OF THE STUDY: PCR screening revealed the significant presence of the genetic markers of Shiga toxin-producing Escherichia coli (STEC) (stx⁺ /stx⁺ eae⁺ ) on the surfaces of sheep carcasses. Citrobacter braakii (stx₁ ⁺ eae⁺ ) was isolated for the first time in this study. The risk of foodborne diseases due to STEC must be taken into account in Algeria. To prevent the emergence of epidemic outbreaks among children and older by people, preventive measures should be taken.

The 2011 German Enterohemorrhagic Escherichia Coli O104:H4 Outbreak-The Danger Is Still Out There

Enterohemorrhagic Escherichia coli (EHEC) are Shiga toxin (Stx) producing bacteria causing a disease characterized by bloody (or non-bloody) diarrhea, which might progress to hemolytic uremic syndrome (HUS). EHEC O104:H4 caused the largest ever recorded EHEC outbreak in Germany in 2011, which in addition showed the so far highest incidence rate of EHEC-related HUS worldwide. The aggressive outbreak strain carries an unusual combination of virulence traits characteristic to both EHEC-a chromosomally integrated Stx-encoding bacteriophage, and enteroaggregative Escherichia coli-pAA plasmid-encoded aggregative adherence fimbriae mediating its tight adhesion to epithelia cells. There are currently still open questions regarding the 2011 EHEC outbreak, e.g., with respect to the exact molecular mechanisms resulting in the hypervirulence of the strain, the natural reservoir of EHEC O104:H4, and suitable therapeutic strategies. Nevertheless, our knowledge on these issues has substantially expanded since 2011. Here, we present an overview of the epidemiological, clinical, microbiological, and molecular biological data available on the 2011 German EHEC O104:H4 outbreak.

Advances in our understanding of the pathogenesis of hemolytic uremic syndromes

Hemolytic uremic syndrome (HUS) is major global health care issue as it is the leading cause of acute kidney injury in children. It is a triad of acute kidney injury, microangiopathic hemolytic anemia, and thrombocytopenia. In recent years, major advances in our understanding of complement-driven inherited rare forms of HUS have been achieved. However, in children 90% of cases of HUS are associated with a Shiga toxin-producing enteric pathogen. The precise pathological mechanisms in this setting are yet to be elucidated. The purpose of this review is to discuss advances in our understanding of the pathophysiology underlying HUS and identify the key questions yet to be answered by the scientific community.

Why Bacteriophage Encode Exotoxins and other Virulence Factors

This study considers gene location within bacteria as a function of genetic element mobility. Our emphasis is on prophage encoding of bacterial virulence factors (VFs). At least four mechanisms potentially contribute to phage encoding of bacterial VFs: (i) Enhanced gene mobility could result in greater VF gene representation within bacterial populations. We question, though, why certain genes but not others might benefit from this mobility. (ii) Epistatic interactions—between VF genes and phage genes that enhance VF utility to bacteria—could maintain phage genes via selection acting on individual, VF-expressing bacteria. However, is this mechanism sufficient to maintain the rest of phage genomes or, without gene co-regulation, even genetic linkage between phage and VF genes? (iii) Phage could amplify VFs during disease progression by carrying them to otherwise commensal bacteria colocated within the same environment. However, lytic phage kill bacteria, thus requiring assumptions of inclusive fitness within bacterial populations to explain retention of phage-mediated VF amplification for the sake of bacterial utility. Finally, (iv) phage-encoded VFs could enhance phage Darwinian fitness, particularly by acting as ecosystem-modifying agents. That is, VF-supplied nutrients could enhance phage growth by increasing the density or by improving the physiology of phage-susceptible bacteria. Alternatively, VF-mediated break down of diffusion-inhibiting spatial structure found within the multicellular bodies of host organisms could augment phage dissemination to new bacteria or to environments. Such phage-fitness enhancing mechanisms could apply particularly given VF expression within microbiologically heterogeneous environments, ie, ones where phage have some reasonable potential to acquire phage-susceptible bacteria.

Induction of Shiga Toxin-Encoding Prophage by Abiotic Environmental Stress in Food

The prophage-encoded Shiga toxin is a major virulence factor in Stx-producing Escherichia coli (STEC). Toxin production and phage production are linked and occur after induction of the RecA-dependent SOS response. However, food-related stress and Stx-prophage induction have not been studied at the single-cell level. This study investigated the effects of abiotic environmental stress on stx expression by single-cell quantification of gene expression in STEC O104:H4 Δstx2::gfp::amp^r In addition, the effect of stress on production of phage particles was determined. The lethality of stressors, including heat, HCl, lactic acid, hydrogen peroxide, and high hydrostatic pressure, was selected to reduce cell counts by 1 to 2 log CFU/ml. The integrity of the bacterial membrane after exposure to stress was measured by propidium iodide (PI). The fluorescent signals of green fluorescent protein (GFP) and PI were quantified by flow cytometry. The mechanism of prophage induction by stress was evaluated by relative gene expression of recA and cell morphology. Acid (pH < 3.5) and H₂O₂ (2.5 mM) induced the expression of stx₂ in about 18% and 3% of the population, respectively. The mechanism of prophage induction by acid differs from that of induction by H₂O₂ H₂O₂ induction but not acid induction corresponded to production of infectious phage particles, upregulation of recA, and cell filamentation. Pressure (200 MPa) or heat did not induce the Stx2-encoding prophage (Stx2-prophage). Overall, the quantification method developed in this study allowed investigation of prophage induction and physiological properties at the single-cell level. H₂O₂ and acids mediate different pathways to induce Stx2-prophage.IMPORTANCE Induction of the Stx-prophage in STEC results in production of phage particles and Stx and thus relates to virulence as well as the transduction of virulence genes. This study developed a method for a detection of the induction of Stx-prophages at the single-cell level; membrane permeability and an indication of SOS response to environmental stress were additionally assessed. H₂O₂ and mitomycin C induced expression of the prophage and activated a SOS response. In contrast, HCl and lactic acid induced the Stx-prophage but not the SOS response. The lifestyle of STEC exposes the organism to intestinal and extraintestinal environments that impose oxidative and acid stress. A more thorough understanding of the influence of food processing-related stressors on Stx-prophage expression thus facilitates control of STEC in food systems by minimizing prophage induction during food production and storage.

How Do the Virulence Factors of Shigella Work Together to Cause Disease?

Shigella is the major cause of bacillary dysentery world-wide. It is divided into four species, named S. flexneri, S. sonnei, S. dysenteriae, and S. boydii, which are distinct genomically and in their ability to cause disease. Shigellosis, the clinical presentation of Shigella infection, is characterized by watery diarrhea, abdominal cramps, and fever. Shigella's ability to cause disease has been attributed to virulence factors, which are encoded on chromosomal pathogenicity islands and the virulence plasmid. However, information on these virulence factors is not often brought together to create a detailed picture of infection, and how this translates into shigellosis symptoms. Firstly, Shigella secretes virulence factors that induce severe inflammation and mediate enterotoxic effects on the colon, producing the classic watery diarrhea seen early in infection. Secondly, Shigella injects virulence effectors into epithelial cells via its Type III Secretion System to subvert the host cell structure and function. This allows invasion of epithelial cells, establishing a replicative niche, and causes erratic destruction of the colonic epithelium. Thirdly, Shigella produces effectors to down-regulate inflammation and the innate immune response. This promotes infection and limits the adaptive immune response, causing the host to remain partially susceptible to re-infection. Combinations of these virulence factors may contribute to the different symptoms and infection capabilities of the diverse Shigella species, in addition to distinct transmission patterns. Further investigation of the dominant species causing disease, using whole-genome sequencing and genotyping, will allow comparison and identification of crucial virulence factors and may contribute to the production of a pan-Shigella vaccine.

Shiga Toxin 1-Producing Shigella sonnei Infections, California, United States, 2014-2015

Shiga toxins (Stx) are primarily associated with Shiga toxin–producing Escherichia coli and Shigella dysenteriae serotype 1. Stx production by other shigellae is uncommon, but in 2014, Stx1-producing S. sonnei infections were detected in California. Surveillance was enhanced to test S. sonnei isolates for the presence and expression of stx genes, perform DNA subtyping, describe clinical and epidemiologic characteristics of case-patients, and investigate for sources of infection. During June 2014–April 2015, we identified 56 cases of Stx1-producing S. sonnei, in 2 clusters. All isolates encoded stx₁ and produced active Stx1. Multiple pulsed-field gel electrophoresis patterns were identified. Bloody diarrhea was reported by 71% of case-patients; none had hemolytic uremic syndrome. Some initial cases were epidemiologically linked to travel to Mexico, but subsequent infections were transmitted domestically. Continued surveillance of Stx1-producing S. sonnei in California is necessary to characterize its features and plan for reduction of its spread in the United States.

Are Escherichia coli Pathotypes Still Relevant in the Era of Whole-Genome Sequencing?

The empirical and pragmatic nature of diagnostic microbiology has given rise to several different schemes to subtype E.coli, including biotyping, serotyping, and pathotyping. These schemes have proved invaluable in identifying and tracking outbreaks, and for prognostication in individual cases of infection, but they are imprecise and potentially misleading due to the malleability and continuous evolution of E. coli. Whole genome sequencing can be used to accurately determine E. coli subtypes that are based on allelic variation or differences in gene content, such as serotyping and pathotyping. Whole genome sequencing also provides information about single nucleotide polymorphisms in the core genome of E. coli, which form the basis of sequence typing, and is more reliable than other systems for tracking the evolution and spread of individual strains. A typing scheme for E. coli based on genome sequences that includes elements of both the core and accessory genomes, should reduce typing anomalies and promote understanding of how different varieties of E. coli spread and cause disease. Such a scheme could also define pathotypes more precisely than current methods.

Stress-Induced Evolution of Heat Resistance and Resuscitation Speed in Escherichia coli O157:H7 ATCC 43888

The development of resistance in foodborne pathogens to food preservation techniques is an issue of increasing concern, especially in minimally processed foods where safety relies on hurdle technology. In this context, mild heat can be used in combination with so-called nonthermal processes, such as high hydrostatic pressure (HHP), at lower individual intensities to better retain the quality of the food. However, mild stresses may increase the risk of (cross-)resistance development in the surviving population, which in turn might compromise food safety. In this investigation, we examined the evolution of Escherichia coli O157:H7 strain ATCC 43888 after recurrent exposure to progressively intensifying mild heat shocks (from 54.0°C to 60.0°C in 0.5°C increments) with intermittent resuscitation and growth of survivors. As such, mutant strains were obtained after 10 cycles of selection with ca. 10⁶-fold higher heat resistance than that for the parental strain at 58.0°C, although this resistance did not extend to temperatures exceeding 60.0°C. Moreover, these mutant strains typically displayed cross-resistance against HHP shock and displayed signs of enhanced RpoS and RpoH activity. Interestingly, additional cycles of selection maintaining the intensity of the heat shock constant (58.5°C) selected for mutant strains in which resuscitation speed, rather than resistance, appeared to be increased. Therefore, it seems that resistance and resuscitation speed are rapidly evolvable traits in E. coli ATCC 43888 that can compromise food safety.

IMPORTANCE

In this investigation, we demonstrated that Escherichia coli O157:H7 ATCC 43888 rapidly acquires resistance to mild heat exposure, with this resistance yielding cross-protection to high hydrostatic pressure treatment. In addition, mutants of E. coli ATCC 43888 in which resuscitation speed, rather than resistance, appeared to be improved were selected. As such, both resistance and resuscitation speed seem to be rapidly evolvable traits that can compromise the control of foodborne pathogens in minimal processing strategies, which rely on the efficacy of combined mild preservation stresses for food safety.

Lipopolysaccharide Induces Human Pulmonary Micro-Vascular Endothelial Apoptosis via the YAP Signaling Pathway

Gram-negative bacterial lipopolysaccharide (LPS) induces a pathologic increase in lung vascular leakage under septic conditions. LPS-induced human pulmonary micro-vascular endothelial cell (HPMEC) apoptosis launches and aggravates micro-vascular hyper-permeability and acute lung injury (ALI). Previous studies show that the activation of intrinsic apoptotic pathway is vital for LPS-induced EC apoptosis. Yes-associated protein (YAP) has been reported to positively regulate intrinsic apoptotic pathway in tumor cells apoptosis. However, the potential role of YAP protein in LPS-induced HPMEC apoptosis has not been determined. In this study, we found that LPS-induced activation and nuclear accumulation of YAP accelerated HPMECs apoptosis. LPS-induced YAP translocation from cytoplasm to nucleus by the increased phosphorylation on Y357 resulted in the interaction between YAP and transcription factor P73. Furthermore, inhibition of YAP by small interfering RNA (siRNA) not only suppressed the LPS-induced HPMEC apoptosis but also regulated P73-mediated up-regulation of BAX and down-regulation of BCL-2. Taken together, our results demonstrated that activation of the YAP/P73/(BAX and BCL-2)/caspase-3 signaling pathway played a critical role in LPS-induced HPMEC apoptosis. Inhibition of the YAP might be a potential therapeutic strategy for lung injury under sepsis.

Animal Models of Enterohemorrhagic Escherichia coli Infection

The first major outbreaks caused by enterohemorrhagic Escherichia coli (EHEC) raised public and medical awareness of the risks associated with acquiring this potentially deadly infection. The widespread presence of these organisms in the environment, the severity of the clinical sequelae, and the lack of treatment options and effective preventive measures demand that we obtain a better understanding of how this group of organisms cause disease. Animal models allow study of the processes and factors that contribute to disease and, as such, form a valuable tool in the repertoire of infectious disease researchers. Yet despite more than 30 years of research, it seems that no single model host reproduces the full spectrum of clinical disease induced by EHEC in humans. In the first part of this review, a synopsis of what is known about EHEC infections is garnered from human outbreaks and biopsy specimens. The main features and limitations of EHEC infection models that are based on the three most commonly used species (pigs, rabbits, and mice) are described within a historical context. Recent advances are highlighted, and a brief overview of models based on other species is given. Finally, the impact of the host on moderating EHEC infection is considered in light of growing evidence for the need to consider the biology and virulence strategies of EHEC in the context of its niche within the intestine.

Different roles of the C-terminal end of Stx1A and Stx2A for AB5 complex integrity and retrograde transport of Stx in HeLa cells

Shiga toxin 1 (Stx1) and Shiga toxin 2 (Stx2) differ regarding receptor affinity, cellular toxicity and clinical outcome. To this date, it is not clarified in detail why the subtypes display these differences. Even though the crystal structures of Stx1 and Stx2 share overall similarities, significant differences were found in the C-terminal end of the A-subunits. The aim of this study was to investigate the role of the C-terminal end of the A-subunit in complex stability and retrograde transport by generating truncated mutants where 2, 4, 6 and 8 amino acids were removed from the C-terminal end of Stx1A and Stx2A. The results obtained show that removal of 6 or 8 amino acids from the Stx1A C-terminus abolishes the AB5 complex integrity, while removing up to 8 amino acids from Stx2A does not affect the complex in vivo (in the bacteria). We also present results showing different levels of A1-subunit in HeLa cells after exposure to Stx1, Stx2 and their truncated mutants.

Bovine macrophages sense Escherichia coli Shiga toxin 1

Shiga toxin (Stx)-producing Escherichia coli (STEC) infections in cattle are asymptomatic; however, Stx impairs the initiation of an adaptive immune response by targeting bovine peripheral and intraepithelial lymphocytes. As presumptive bovine mucosal macrophages (Mø) are also sensitive to Stx, STEC may even exert immune modulatory effects by acting on steps preceding lymphocyte activation at the Mø level. We therefore studied the expression of the Stx receptor (CD77), cellular phenotype and functions after incubation of primary bovine monocyte-derived Mø with purified Stx1. A significant portion of bovine Mø expressed CD77 on their surface, with the recombinant B-subunit of Stx1 binding to >50% of the cells. Stx1 down-regulated significantly surface expression of CD14, CD172a and co-stimulatory molecules CD80 and CD86 within 4 h of incubation, while MHC-II expression remained unaffected. Furthermore, incubation of Mø with Stx1 increased significantly numbers of transcripts for IL-4, IL-6, IL-10, IFN-γ, TNF-α, IL-8 and GRO-α but not for IL-12, TGF-β, MCP-1 and RANTES. In the course of bovine STEC infections, Stx1 appears to induce in Mø a mixed response pattern reminiscent of regulatory Mø, which may amplify the direct suppressive effect of the toxin on lymphocytes.

Evaluation of biological safety in vitro and immunogenicity in vivo of recombinant Escherichia coli Shiga toxoids as candidate vaccines in cattle

Cattle are the most important reservoir for enterohemorrhagic Escherichia coli (EHEC), a subset of shigatoxigenic E. coli (STEC) capable of causing life-threatening infectious diseases in humans. In cattle, Shiga toxins (Stx) suppress the immune system thereby promoting long-term STEC shedding. First infections of animals at calves’ age coincide with the lack of Stx-specific antibodies. We hypothesize that vaccination of calves against Shiga toxins prior to STEC infection may help to prevent the establishment of a persistent type of infection. The objectives of this study were to generate recombinant Shiga toxoids (rStx1_mut & rStx2_mut) by site-directed mutagenesis and to assess their immunomodulatory, antigenic, and immunogenic properties. Cultures of bovine primary immune cells were used as test systems. In ileal intraepithelial lymphocytes both, recombinant wild type Stx1 (rStx1_WT) and rStx2_WT significantly induced transcription of IL-4 mRNA. rStx1_WT and rStx2_WT reduced the expression of Stx-receptor CD77 (syn. Globotriaosylceramide, Gb3) on B and T cells from peripheral blood and of CD14 on monocyte-derived macrophages. At the same concentrations, rStx1_mut and rStx2_mut exhibited neither of these effects. Antibodies in sera of cattle naturally infected with STEC recognized the rStx_mut toxoids equally well as the recombinant wild type toxins. Immunization of calves with rStx1_mut plus rStx2_mut led to induction of antibodies neutralizing Stx1 and Stx2. While keeping their antigenicity and immunogenicity recombinant Shiga toxoids are devoid of the immunosuppressive properties of the corresponding wild type toxins in cattle and candidate vaccines to mitigate long-term STEC shedding by the reservoir host.

Sequence comparison and phylogenetic analysis by the Maximum Likelihood method of ribosome-inactivating proteins from angiosperms

Ribosome-inactivating proteins (RIPs) from angiosperms are rRNA N-glycosidases that have been proposed as defence proteins against virus and fungi. They have been classified as type 1 RIPs, consisting of single-chain proteins, and type 2 RIPs, consisting of an A chain with RIP properties covalently linked to a B chain with lectin properties. In this work we have carried out a broad search of RIP sequence data banks from angiosperms in order to study their main structural characteristics and phylogenetic evolution. The comparison of the sequences revealed the presence, outside of the active site, of a novel structure that might be involved in the internal protein dynamics linked to enzyme catalysis. Also the B-chains presented another conserved structure that might function either supporting the beta-trefoil structure or in the communication between both sugar-binding sites. A systematic phylogenetic analysis of RIP sequences revealed that the most primitive type 1 RIPs were similar to that of the actual monocots (Poaceae and Asparagaceae). The primitive RIPs evolved to the dicot type 1 related RIPs (like those from Caryophyllales, Lamiales and Euphorbiales). The gene of a type 1 RIP related with the actual Euphorbiaceae type 1 RIPs fused with a double beta trefoil lectin gene similar to the actual Cucurbitaceae lectins to generate the type 2 RIPs and finally this gene underwent deletions rendering either type 1 RIPs (like those from Cucurbitaceae, Rosaceae and Iridaceae) or lectins without A chain (like those from Adoxaceae).

Atypical haemolytic uraemic syndrome associated with a CD46 mutation triggered by Shigella flexneri

We present a case of haemolytic uraemic syndrome (HUS) triggered by Shigella flexneri. Of the Shigella species, only S. dysenteriae type 1 is said to produce Shiga toxin and consequently cause HUS. Investigation of the complement system in this patient revealed a CD46 mutation. In individuals with mutations in complement genes incomplete penetrance of atypical HUS (aHUS) is seen, suggesting that a trigger, such as infection, is required for disease to manifest. In an era of complement modulatory therapy for aHUS it is important to be alert to unusual presentations of diarrhoeal-associated disease.

Hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy defined by thrombocytopenia, nonimmune microangiopathic hemolytic anemia, and acute renal failure. The most frequent form is associated with infections by Shiga-like toxin-producing bacteria (STEC-HUS). Rarer cases are triggered by neuraminidase-producing Streptococcus pneumoniae (pneumococcal-HUS). The designation of aHUS is used to refer to those cases in which an infection by Shiga-like toxin-producing bacteria or S. pneumoniae can be excluded. Studies performed in the last two decades have documented that hyperactivation of the complement system is the pathogenetic effector mechanism leading to the endothelial damage and the microvascular thrombosis in aHUS. Recent data suggested the involvement of the complement system in the pathogenesis of STEC-HUS and pneumococcal-HUS as well. Clinical signs and symptoms may overlap among the different forms of HUS; however, pneumococcal-HUS and aHUS have a worse prognosis compared with STEC-HUS. Early diagnosis and identification of underlying pathogenetic mechanism allows instating specific support measures and therapies. In clinical trials in patients with aHUS, complement inhibition by eculizumab administration leads to a rapid and sustained normalization of hematological parameters with improvement in long-term renal function. This review summarizes current concepts about the epidemiological findings, the pathological and clinical aspects of STEC-HUS, pneumococcal-HUS, and aHUS, and their diagnosis and management.

Optimization of furin inhibitors to protect against the activation of influenza hemagglutinin H5 and Shiga toxin

Proprotein convertases (PCs) are crucial in the processing and entry of viral or bacterial protein precursors and confer increased infectivity of pathogens bearing a PC activation site, which results in increased symptom severity and lethality. Previously, we developed a nanomolar peptide inhibitor of PCs to prevent PC activation of infectious agents. Herein, we describe a peptidomimetic approach that increases the stability of this inhibitor for use in vivo to prevent systemic infections and cellular damage, such as that caused by influenza H5N1 and Shiga toxin. The addition of azaβ(3)-amino acids to both termini of the peptide successfully prevented influenza hemagglutinin 5 fusogenicity and Shiga toxin Vero toxicity in cell-based assays. The results from a cell-based model using stable shRNA-induced proprotein convertase knockdown indicate that only furin is the major proprotein convertase required for HA5 cleavage.

Two patients with history of STEC-HUS, posttransplant recurrence and complement gene mutations

Hemolytic uremic syndrome (HUS) is a disease of microangiopathic hemolytic anemia, thrombocytopenia and acute renal failure. About 90% of cases are secondary to infections by Escherichia coli strains producing Shiga-like toxins (STEC-HUS), while 10% are associated with mutations in genes encoding proteins of complement system (aHUS). We describe two patients with a clinical history of STEC-HUS, who developed end-stage renal disease (ESRD) soon after disease onset. They received a kidney transplant but lost the graft for HUS recurrence, a complication more commonly observed in aHUS. Before planning a second renal transplantation, the two patients underwent genetic screening for aHUS-associated mutations that revealed the presence of a heterozygous CFI mutation in patient #1 and a heterozygous MCP mutation in patient #2, and also in her mother who donated the kidney. This finding argues that the two cases originally diagnosed as STEC-HUS had indeed aHUS triggered by STEC infection on a genetic background of impaired complement regulation. Complement gene sequencing should be performed before kidney transplantation in patients who developed ESRD following STEC-HUS since they may be undiagnosed cases of aHUS, at risk of posttransplant recurrence. Furthermore, genetic analysis of donors is mandatory before living-related transplantation to exclude carriers of HUS-predisposing mutations.

Shiga toxin-producing Escherichia coli isolated from chicken meat in Iran: serogroups, virulence factors, and antimicrobial resistance properties

The aim of the current study was to determine the virulence factors, serogroups, and antibiotic resistance properties of Shiga toxin-producing Escherichia coli isolated from chicken meat samples. A total of 422 chicken meat samples were collected from 5 townships of Iran. Specimens were immediately transferred to the laboratory in a cooler with an ice pack. Samples were cultured, and the positive culture samples were analyzed by PCR assays. Finally, the antimicrobial susceptibility test was performed using the disk diffusion method in Mueller-Hinton agar. According to the results, out of 422 samples, 146 (34.59%) were confirmed to be E. coli positive and among E. coli-positive samples, 51 (34.93%) and 31 (21.23%) were from attaching and effacing E. coli (AEEC) and enterohemorrhagic E. coli (EHEC) subgroups, respectively. All of the EHEC-positive samples had all stx1, eaeA, and ehly virulence genes, whereas only 5 (9.80%) of AEEC subgroup had all stx1, stx2, and eaeA genes. As the data revealed, O157 was the most prevalent and O111 was the least prevalent strains in the Shiga toxin-producing E. coli (STEC) population. Among STEC strains, sulI and blaSHV had the highest and lowest incidence rate, respectively. There was a high resistance to tetracycline (76.82%), followed by chloramphenicol (73.17%) and nitrofurantoin (63.41%), but there was low resistance to cephalotine (7.31%) antibiotics in isolated strains. Results shows that the PCR technique has a high performance for detection of serogroups, virulence genes, and antibiotic resistance genes in STEC strains. This study is the first prevalence report of detection of virulence genes, serogroups, and antibiotic resistance properties of STEC strains isolated from chicken meat samples in Iran. Based on the results, chicken meat is one of the main sources of STEC strains and its virulence factors in Iran, so an accurate meat inspection would reduce disease outbreaks.

Loss of cAMP/CRP regulation confers extreme high hydrostatic pressure resistance in Escherichia coli O157:H7

Application of high hydrostatic pressure (HHP) constitutes a valuable non-thermal pasteurization process in modern food conservation. Triggered by our interest in the rapid adaptive evolution towards HHP resistance in the food-borne pathogen E. coli O157:H7 (strain ATCC 43888) that was demonstrated earlier, we used genetic screening to identify specific loci in which a loss-of-function mutation would be sufficient to markedly increase HHP survival. As such, individual loss of RssB (anti RpoS-factor), CRP (catabolite response protein) and CyaA (adenylate cyclase) were each found to confer significant HHP resistance in the 300MPa range (i.e. >1,000-fold), and this phenotype invariably coincided with increased resistance against heat as well. In contrast to loss of RssB, however, loss of CRP or CyaA also conferred significantly increased resistance to 600MPa (i.e. >10,000-fold), suggesting cAMP/CRP homeostasis to affect extreme HHP resistance independently of increased RpoS activity. Surprisingly, none of the rapidly emerging HHP-resistant mutants of ATCC 43888 that were isolated previously did incur any mutations in rssB, crp or cyaA, indicating that a number of other loci can guide the rapid emergence of HHP resistance in E. coli O157:H7 as well. The inability of spontaneous rssB, crp or cyaA mutants to emerge during selective enrichment under HHP selection likely stems from their decreased competitive fitness during growth. Overall, this study is the first to shed light on the possible genetic strategies supporting the acquisition of HHP resistance in E. coli O157:H7.

Gastrointestinal and extra-intestinal manifestations of childhood shigellosis in a region where all four species of Shigella are endemic

Objective

To determine the clinical manifestations and outcome of shigellosis among children infected with different species of Shigella.

Methods

We identified all patients <15 years infected with Shigella admitted to the icddr, b Dhaka hospital during one year. Study staff reviewed admission records and repeated the physical examinations and history of patients daily.

Results

Of 792 children with shigellosis 63% were infected with S. flexneri, 20% with S. dysenteriae type 1, 10% with S. boydii, 4% with S. sonnei, and 3% with S. dysenteriae types 2–10. Children infected with S. dysenteriae type 1, when compared to children infected with other species, were significantly (P<0.05) more likely to have severe gastrointestinal manifestations: grossly bloody stools (78% vs. 33%), more stools in the 24 h before admission (median 25 vs. 11), and rectal prolapse (52% vs. 15%) - and extra-intestinal manifestations - leukemoid reaction (22% vs. 2%), hemolytic-uremic syndrome (8% vs. 1%), severe hyponatremia (58% vs. 26%) and neurologic abnormalities (24% vs. 16%). The overall fatality rate was 10% and did not differ significantly by species. In a multiple regression analysis young age, malnutrition, hyponatremia, lesser stool frequency, documented seizure, and unconsciousness were predictive of death.

Conclusions

Both severe intestinal disease and extra-intestinal manifestations of shigellosis occur with infection by any of the four species of Shigella, but are most common with S. dysenteriae type 1. Among these inpatient children, the risk of death was high with infection of any of the four Shigella species.

Functional capacity of Shiga-toxin promoter sequences in eukaryotic cells

Shiga toxins (Stx) are the main virulence factors in enterohemorrhagic Escherichia coli (EHEC) infections, causing diarrhea and hemolytic uremic syndrome (HUS). The genes encoding for Shiga toxin-2 (Stx2) are located in a bacteriophage. The toxin is formed by a single A subunit and five B subunits, each of which has its own promoter sequence. We have previously reported the expression of the B subunit within the eukaryotic environment, probably driven by their own promoter. The aim of this work was to evaluate the ability of the eukaryotic machinery to recognize stx2 sequences as eukaryotic-like promoters. Vero cells were transfected with a plasmid encoding Stx2 under its own promoter. The cytotoxic effect on these cells was similar to that observed upon incubation with purified Stx2. In addition, we showed that Stx2 expression in Stx2-insensitive BHK eukaryotic cells induced drastic morphological and cytoskeletal changes. In order to directly evaluate the capacity of the wild promoter sequences of the A and B subunits to drive protein expression in mammalian cells, GFP was cloned under eukaryotic-like putative promoter sequences. GFP expression was observed in 293T cells transfected with these constructions. These results show a novel and alternative way to synthesize Stx2 that could contribute to the global understanding of EHEC infections with immediate impact on the development of treatments or vaccines against HUS.

Exposure to high hydrostatic pressure rapidly selects for increased RpoS activity and general stress-resistance in Escherichia coli O157:H7

Exposure to high hydrostatic pressure (HHP) is increasingly being used in food preservation as a non-thermal pasteurization process, and its further implementation necessitates a more thorough understanding of bacterial resistance development and intraspecies variability with regard to inactivation by HHP. In this report, we discovered that exposure to high hydrostatic pressure stress can rapidly select for strongly increased RpoS activity in a hypersensitive Escherichia coli O157:H7 strain (ATCC 43888), leading to a simultaneous increase in HHP and heat resistance. Moreover, the level of RpoS activity correlated well with the original hypersensitivity and the extent of acquired HHP resistance, and extremely HHP-resistant mutants of ATCC 43888 clearly incurred a number of additional RpoS-dependent phenotypes. These findings suggest that implementation of novel processing techniques in the food production chain can readily affect the physiology of food-borne pathogens.

Lactobacillus plantarum isolated from kefir protects vero cells from cytotoxicity by type-II shiga toxin from Escherichia coli O157:H7

Kefir is a fermented-milk beverage originating and widely consumed in the Caucasus as well as in Eastern Europe and is a source of bacteria with potential probiotic properties. Enterohaemorrhagic Escherichia coli producing Shiga toxin is commonly associated with food-transmitted diseases; the most prevalent serotype causing epidemics is Esch. coli O157:H7. The aim of this study was to evaluate the antagonism of Lactobacillus plantarum isolated from kefir against the action on Vero cells of supernatants of the Esch. coli O157:H7 strain 69160 expressing the type-II Shiga toxin (Stx2) and to study the role of the Lactobacillus cell wall in that inhibition. Spent culture supernatants of Esch. coli O157:H7 strain 69160 led to cytotoxic effects on cultured eukaryotic cells as evidenced by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide-cleavage assay or by lactate-dehyrogenase release. Lb. plantarum CIDCA 83114 reduced the cytotoxic activity of Stx present in strain-69160 supernatants, and this protection was markedly higher than those of Lactobacillus kefir CIDCA 83113 and 8348 and Lb. delbrueckii subsp. bulgaricus CIDCA 333. This antagonism of cytotoxicity was mimicked by Lb. plantarum cell walls but was reduced after heating or protease treatments, thus indicating a protein or peptide as being involved in the protection mechanism. The cell surface of the lactobacilli bound the subunit B of Stx thereby decreasing the cytotoxicity. These interactions could constitute the first step in preventing the damage induced by Esch. coli O157:H7 supernatants, thus representing a valuable means of potentially mitigating the noxious effects of this food pathogen.

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.

Differences in Shiga toxin and phage production among stx(2g)-positive STEC strains

Shiga toxin-producing Escherichia coli (STEC) are characterized by the production of Shiga toxins (Stx) encoded by temperate bacteriophages. Stx production is linked to the induction of the phage lytic cycle. Several stx variants have been described and differentially associated with the risk of developing severe illness. The variant named stx(2g) was first identified in a STEC strain isolated from the faeces of healthy cattle. Analysis of stx(2g)-positive strains isolated from humans, animals, and environmental sources have shown that they have a close relationship. In this study, stx(2g)-positive STEC isolated from cattle were analyzed for phage and Stx production, with the aim to relate the results to differences observed in cytotoxicity. The presence of inducible phages was assessed by analyzing the bacterial growth/lysis curves and also by plaque assay. Bacterial growth curves in the absence of induction were similar for all isolates, however, notably differed among induced cultures. The two strains that clearly evidenced bacteriolysis under this condition also showed higher phage titers in plaque assays. However, only the phage plaques produced by one of these strains (FB 62) hybridized with a stx(2)-probe. Furthermore, the production of Stx was evaluated by enzyme immunoassay (EIA) and Western immunoblotting in overnight supernatants. By EIA, we detected Stx only in supernatants of FB 62, with a higher signal for induced than uninduced cultures. By immunoblotting, Stx2 could be detected after induction in all stx(2g)-positive isolates, but with lower amounts of Stx2B subunit in those supernatants where phages could not be detected. Taking into account all the results, several differences could be found among stx(2g)-positive strains. The strain with the highest cytotoxic titer showed higher levels of stx(2)-phages and toxin production by EIA, and the opposite was observed for strains that previously showed low cytotoxic titers, confirming that in stx(2g)-positive strains Stx production is phage-regulated.