A novel Shiga toxin 2a neutralizing antibody therapeutic with low immunogenicity and high efficacy

Shiga toxin-producing Escherichia coli infections are difficult to treat due to the risk of antibiotic-induced stress upregulating the production of toxins, medical treatment is consequently limited to supportive care to prevent the development of hemolytic uremic syndrome (HUS). Here, we introduce a potentially therapeutic humanized mouse monoclonal antibody (Hu-mAb 2-5) targeting Stx2a, the most common Shiga toxin subtype identified from outbreaks. We demonstrate that Hu-mAb 2-5 has low immunogenicity in healthy adults ex vivo and high neutralizing efficacy in vivo, protecting mice from mortality and HUS-related tissue damage.

Red blood cell-derived arginase release in hemolytic uremic syndrome

BACKGROUND

Hemolysis is a cardinal feature of hemolytic uremic syndrome (HUS) and during hemolysis excess arginase 1 is released from red blood cells. Increased arginase activity leads to reduced L-arginine, as it is converted to urea and L-ornithine, and thereby reduced nitric oxide bioavailability, with secondary vascular injury. The objective of this study was to investigate arginase release in HUS patients and laboratory models and correlate arginase levels to hemolysis and kidney injury.

METHODS

Two separate cohorts of patients (n = 47 in total) with HUS associated with Shiga toxin-producing enterohemorrhagic E. coli (EHEC) and pediatric controls (n = 35) were investigated. Two mouse models were used, in which mice were either challenged intragastrically with E. coli O157:H7 or injected intraperitoneally with Shiga toxin 2. An in vitro model of thrombotic microangiopathy was developed in which Shiga toxin 2- and E. coli O157 lipopolysaccharide-stimulated human blood cells combined with ADAMTS13-deficient plasma were perfused over glomerular endothelial cells. Two group statistical comparisons were performed using the Mann-Whitney test, multiple groups were compared using the Kruskal-Wallis test followed by Dunn's procedure, the Wilcoxon signed rank test was used for paired data, or linear regression for continuous variables.

RESULTS

HUS patients had excessively high plasma arginase 1 levels and activity (conversion of L-arginine to urea and L-ornithine) during the acute phase, compared to remission and controls. Arginase 1 levels correlated with lactate dehydrogenase activity, indicating hemolysis, as well as the need for dialysis treatment. Patients also exhibited high levels of plasma alpha-1-microglobulin, a heme scavenger. Both mouse models exhibited significantly elevated plasma arginase 1 levels and activity. Plasma arginase 1 levels correlated with lactate dehydrogenase activity, alpha-1-microglobulin and urea levels, the latter indicative of kidney dysfunction. In the in vitro model of thrombotic microangiopathy, bioactive arginase 1 was released and levels correlated to the degree of hemolysis.

CONCLUSIONS

Elevated red blood cell-derived arginase was demonstrated in HUS patients and in relevant in vivo and in vitro models. The excessively high arginase levels correlated to the degree of hemolysis and kidney dysfunction. Thus, arginase inhibition should be investigated in HUS.

Detection of Cleaved Stx2a in the Blood of STEC-Infected Patients

Typical hemolytic uremic syndrome (HUS) is mainly caused by Shiga toxin-producing Escherichia coli (STEC) releasing Shiga toxin 2 (Stx2). Two different structures of this AB5 toxin have been described: uncleaved, with intact B and A chains, and cleaved, with intact B and a nicked A chain consisting of two fragments, A1 and A2, connected by a disulfide bond. Despite having the same toxic effect on sensitive cells, the two forms differ in their binding properties for circulating cells, serum components and complement factors, thus contributing to the pathogenesis of HUS differently. The outcome of STEC infections and the development of HUS could be influenced by the relative amounts of uncleaved or cleaved Stx2 circulating in patients' blood. Cleaved Stx2 was identified and quantified for the first time in four out of eight STEC-infected patients' sera by a method based on the inhibition of cell-free translation. Cleaved Stx2 was present in the sera of patients with toxins bound to neutrophils and in two out of three patients developing HUS, suggesting its involvement in HUS pathogenesis, although in association with other bacterial or host factors.

Cytotoxic Effects of Recombinant StxA2-His in the Absence of Its Corresponding B-Subunit

AB₅ protein toxins are produced by certain bacterial pathogens and are composed of an enzymatically active A-subunit and a B-subunit pentamer, the latter being responsible for cell receptor recognition, cellular uptake, and transport of the A-subunit into the cytosol of eukaryotic target cells. Two members of the AB₅ toxin family were described in Shiga toxin-producing Escherichia coli (STEC), namely Shiga toxin (Stx) and subtilase cytotoxin (SubAB). The functional paradigm of AB toxins includes the B-subunit being mandatory for the uptake of the toxin into its target cells. Recent studies have shown that this paradigm cannot be maintained for SubAB, since SubA alone was demonstrated to intoxicate human epithelial cells in vitro. In the current study, we raised the hypothesis that this may also be true for the A-subunit of the most clinically relevant Stx-variant, Stx2a. After separate expression and purification, the recombinant Stx2a subunits StxA2a-His and StxB2a-His were applied either alone or in combination in a 1:5 molar ratio to Vero B4, HeLa, and HCT-116 cells. For all cell lines, a cytotoxic effect of StxA2a-His alone was detected. Competition experiments with Stx and SubAB subunits in combination revealed that the intoxication of StxA2a-His was reduced by addition of SubB1-His. This study showed that the enzymatic subunit StxA2a alone was active on different cells and might therefore play a yet unknown role in STEC disease development.

Carboxypeptidase B2 and N play different roles in regulation of activated complements C3a and C5a in mice

Essentials Two basic carboxypeptidases are present in plasma, B2 (CPB2) and N (CPN). Cpb2-/- and Cpn-/- mice were challenged in a hemolytic uremic syndrome (HUS) model vs. wild type. Cpb2-/- exacerbates HUS while Cpn-/- exacerbates cobra venom factor challenge vs. wild type mice. CPB2 and CPN have overlapping but non-redundant roles.

SUMMARY

Background There are two basic carboxypeptidases in plasma. Carboxypeptidase B2 (CPB2) is activated from a circulating zymogen, proCPB2, and carboxypeptidase N (CPN) is constitutively active with both inactivating complement C3a and C5a. Aims To test the roles of CPB2 and CPN in complement-driven mouse models of cobra venom factor (CVF) challenge and hemolytic-uremic syndrome (HUS). Methods Cpb2-/- , Cpn-/- and wild-type (WT) mice were compared in an HUS model induced by Shiga toxin and lipopolysaccharide administration and following CVF administration. Results HUS was exacerbated in Cpb2-/- mice more than in Cpn-/- mice, compared with WT mice. Cpb2-/- mice developed the HUS clinical triad of microangiopathic hemolytic anemia, uremia and thrombocytopenia. Treatment with anti-C5 antibody improved survival of both Cpb2-/- and Cpn-/- mice. In contrast, when challenged acutely with CVF, the reverse phenotype was observed. Cpn-/- mice had markedly worse disease than Cpb2-/- mice, whereas the WT mice were resistant. Conclusions CPN and CPB2 play overlapping but non-redundant roles in regulating complement activation in vivo. The constitutively active CPN is key for inactivation of systemic C5a, whereas CPB2 functions as an on-demand supplementary anaphylatoxin inhibitor in inactivating excessive C5a formed locally.

Arfaptin-1 negatively regulates Arl1-mediated retrograde transport

The small GTPase Arf-like protein 1 (Arl1) is well known for its role in intracellular vesicular transport at the trans-Golgi network (TGN). In this study, we used differential affinity chromatography combined with mass spectrometry to identify Arf-interacting protein 1b (arfaptin-1b) as an Arl1-interacting protein and characterized a novel function for arfaptin-1 (including the arfaptin-1a and 1b isoforms) in Arl1-mediated retrograde transport. Using a Shiga-toxin subunit B (STxB) transportation assay, we demonstrated that knockdown of arfaptin-1 accelerated the retrograde transport of STxB from the endosome to the Golgi apparatus, whereas Arl1 knockdown inhibited STxB transport compared with control cells. Arfaptin-1 overexpression, but not an Arl1 binding-defective mutant (arfaptin-1b-F317A), consistently inhibited STxB transport. Exogenous arfaptin-1 expression did not interfere with the localization of the Arl1-interacting proteins golgin-97 and golgin-245 to the TGN and vice versa. Moreover, we found that the N-terminal region of arfaptin-1 was involved in the regulation of retrograde transport. Our results show that arfaptin-1 acts as a negative regulator in Arl1-mediated retrograde transport and suggest that different functional complexes containing Arl1 form in distinct microdomains and are responsible for different functions.

Role of vascular endothelial growth factor and angiopoietin 1 in renal injury in hemolytic uremic syndrome

BACKGROUND/AIMS

The recovery process from renal injury in hemolytic uremic syndrome (HUS) remains obscure. In order to clarify the role of vascular endothelial growth factor (VEGF) and angiopoietin 1 (Ang-1) in the renal recovery from HUS, we produced a model of mild HUS and examined the renal recovery process.

METHODS

We investigated three groups of mice. Group 1 consisted of mice that received an injection of Shiga toxin 2 (Stx2) and lipopolysaccharide (LPS); group 2 consisted of mice that received an injection of low dose of Stx2 and LPS, and group 3 consisted of control mice.

RESULTS

Serum Cr levels in group 1 were greater than those in group 2, and all mice in group 1 died, whereas all mice in group 2 remained alive. Endothelial injury at 24 h in group 1 was higher than in group 2. Electron-microscopic findings demonstrated that the endothelial cells formed immature capillary-like lumina from 7 to 28 days with increases in the expression of CD31-positive cells. Glomerular VEGF expression decreased at 72 h in group 1, but gradually increased in group 2. Glomerular Ang-1 expression peaked from 72 h to 28 days. Ang-1 expression was frequently found in the endothelial cell region of vesicle walls simultaneous with increased CD31-positive staining.

CONCLUSION

Our findings suggest that VEGF and Ang-1 play important roles in the recovery process, particularly in the regeneration of endothelial injury.

Characterization of stx2 tubular response in a rat experimental model of hemolytic uremic syndrome

BACKGROUND/AIMS

In Argentina, hemolytic uremic syndrome (HUS) constitutes the most frequent cause of acute renal failure in children. The aim of our study was to analyze the early tubular response under the effect of Shiga toxin type 2 (Stx2) in a rat experimental model of HUS.

METHODS

Adult male Sprague-Dawley rats were injected intraperitoneally with culture supernatant from recombinant Escherichia coli expressing Stx2. Functional, histological, immunohistochemical and Western blot studies were performed at 48 h postinoculation.

RESULTS

Renal tubules showed the loss of the epithelial markers E-cadherin and β-catenin, and an increase in transforming growth factor-β1 expression. We detected the expression of α-smooth muscle actin in the interstitium and fibrosis in the periglomerular areas.

CONCLUSION

Our results indicate that the early tubular response to the effects of Stx2 is related to an immunophenotype change of tubular cells and the presence of mild fibrosis in the interstitium.

Renal damage and death in weaned mice after oral infection with Shiga toxin 2-producing Escherichia coli strains

Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 infections are considered a public health problem in both developed and developing countries because of their increasing incidence and the severity of clinical presentation. Approximately 10% of infected patients develop complications such as haemolytic uraemic syndrome (HUS) characterized by acute renal failure, thrombocytopenia and haemolytic anaemia. The precise sequence of events leading to HUS is still understood incompletely. Because of the lack of a reproducible small animal model for EHEC infections, in vivo studies examining EHEC-host early interactions are limited and insufficient. The aim of this study was to characterize the weaned BALB/c mouse as a model of E. coli O157:H7 infection. In this paper we report that human Shiga toxin 2 (Stx2)-producing EHEC strains can adhere to the intestinal epithelium of weaned BALB/c mice, and produce local damage which leads to systemic disease and death in a percentage of infected mice. The lethality of the EHEC strain is closely age-dependent, and is related to the bacterial ability to colonize intestine and to produce Stx2. It can be concluded that the weaned BALB/c mouse can be used as a small animal model to study host early responses, and the role of bacterial pathogenic factors in the induction of systemic disease, thus providing a useful tool for the evaluation of therapeutic or vaccine approaches.

Virulence and fitness gene patterns of Shiga toxin-encoding Escherichia coli isolated from pigs with edema disease or diarrhea in Germany

Fecal Escherichia coli isolates (n = 3,218) from piglets with edema disease or diarrhea were screened for the genes of Stx2 and Stx2 variants. A total of 283 E. coli isolates (8.8%) proved exclusively positive for Stx2e and most of these (85.1%) harbored genes for F18 fimbria. No recognized adhesins were detectable in 14.5% of the isolates. Genes for heat-stable or heat-labile E. coli enterotoxins were found in F18+ as well as F18 isolates (51.9% and 33.3%, respectively). Five isolates also harbored fyuA and irp2 genes which are indicative of a high pathogenicity island in E. coli. All Stx2e+ isolates lacked genes for intimin, EHEC hemolysin, STEC autoagglutinating adhesin, subtilase cytotoxin, serine protease Espl. The majority of Stx2e+ isolates belonged to phylogenetic groups A (59.3%) and D (38.9%) and only few isolates were classified as B1 and B2 (1.8%). The results suggest that Stx2e-producing E. coli strains are highly prevalent in diseased pigs in Germany. Despite their significant diversity, most strains possess all typical features (Stx2e, F18) of porcine edema disease E. coli. However, a considerable portion of porcine strains resembles published human Stx2e+ strains in that they lack any recognized pig-associated adhesin. Thus, a zoonotic potential cannot be excluded for these strains.

A method for fast and simple detection of major diarrhoeagenic Escherichia coli in the routine diagnostic laboratory

A multiplex PCR was developed for the detection of the following genes characteristic of diarrhoeagenic Escherichia coli (DEC): verocytotoxins 1 (vtx1) and 2 (vtx2), characteristic of verocytotoxin-producing E. coli (VTEC); intimin (eae), found in enteropathogenic E. coli (EPEC), attaching and effacing E. coli and VTEC; heat-stable enterotoxin (estA) and heat-labile enterotoxin (eltA), characteristic of enterotoxigenic E. coli (ETEC); and invasive plasmid antigen (ipaH), characteristic of enteroinvasive E. coli (EIEC) and Shigella spp. The method allowed the simultaneous identification of all six genes in one reaction, and included a 16S rDNA internal PCR control. When applied to pure cultures from a reference strain collection, all virulence genes in 124 different DEC strains and 15 Shigella spp. were identified correctly, and there were no cross-reactions with 13 non-E. coli species. The detection limit of the method was 10(2)-10(3) DEC CFU/PCR in the presence of 10(6) non-target cells. When the multiplex PCR was tested with colonies from plate cultures of clinical stool samples, it was a faster, more sensitive, less expensive and less laborious diagnostic procedure than DNA hybridisation. When used with DNA purified from spiked stool samples (by two different commercial kits), the method had a detection limit of 10(6) CFU/mL stool sample.

Serotypes and analysis of distribution of Shiga toxin-producingEscherichia colifrom cattle and sheep in the lower North Island, New Zealand

AIMS

To serotype a subset of Shiga toxin-producing Escherichia coli (STEC) isolates from cattle and sheep to determine whether any corresponding serotypes have been implicated in human diarrhoeal disease, both in New Zealand and worldwide, and to examine the distribution of STEC and enteropathogenic Escherichia coli (EPEC) amongst cattle (calves, heifers and dairy) and sheep (lambs, rams and ewes), to assess whether carriage of identified bacterial genotypes may be associated with a particular age of animal.

METHODS

Recto-anal mucosal swabs (RAMS) were taken from 91 calves, 24 heifers and 72 dairy cattle, and 46 lambs, 50 ewes and 36 rams, from four sites in the Manawatu and Rangitikei regions of New Zealand. Strains of E. coli selected from primary isolation plates were subjected to a multiplex polymerase chain reaction (PCR), to determine the presence of Shiga toxin genes (stx1 and stx2) and the E. coli attaching and effacing gene (eae).

RESULTS

Overall, 186/319 (58.3%) animals sampled were positive for stx1, stx2, or eae isolates. More sheep (43.9%) were stx1-positive than cattle (2.7%; p = 0.036), and amongst sheep more lambs and ewes were stx1-positive than rams (p = 0.036). Amongst cattle, more calves and heifers were eae-positive than dairy cows (p = 0.030). Two or more different STEC were isolated from at least 28 (9%) animals (three cattle and 25 sheep), based on their stx/eae genotype. Enterohaemolysin genes were found in 39/51 (76%) isolates serotyped. Twenty-one different serotypes were detected, including O5:H-, O9:H51, O26:H11, O84:H-/H2 and O149:H8 from cattle, and O26:H11, O65:H-, O75:H8, O84:H-, O91:H-, O128:H2 and O174:H8 from sheep; O84:H-, O26:H11, O5:H-, O91:H- and O128:H2 serotypes have been associated with human disease.

CONCLUSIONS

If nationally representative, this study confirms that cattle and sheep in New Zealand may be a major reservoir of STEC serotypes that have been recognised as causative agents of diarrhoeal disease in humans. Distribution of STEC and EPEC in cattle and sheep indicates that direct contact with, in particular, calves or their faeces, or exposure to environments cross contaminated with ruminant faeces, may represent an increased risk factor for human disease in New Zealand.

Slugs: potential novel vectors of Escherichia coli O157

Field and laboratory studies were performed to determine whether slugs could act as novel vectors for pathogen (e.g., Escherichia coli O157) transfer from animal feces to salad vegetables. Escherichia coli O157 was isolated from 0.21% of field slugs from an Aberdeenshire sheep farm. These isolates carried the verocytotoxin genes (vt1 and vt2) and the attaching and effacing gene (eae), suggesting that they are potentially pathogenic to humans. Strain typing using multilocus variable number tandem repeats analysis showed that slug and sheep isolates were indistinguishable. Laboratory experiments using an E. coli mutant resistant to nalidixic acid showed that the ubiquitous slug species Deroceras reticulatum could carry viable E. coli on its external surface for up to 14 days. Slugs that had been fed E. coli shed viable bacteria in their feces with numbers showing a short but statistically significant linear log decline. Further, it was found that E. coli persisted for up to 3 weeks in excreted slug feces, and hence, we conclude that slugs have the potential to act as novel vectors of E. coli O157.

Prevalence and Characterization ofEscherichia coliO26 and O111 in Retail Minced Beef in Ireland

Verocytotoxigenic Escherichia coli (VTEC) O157 are recognized as bacterial pathogens with significant public health impact. However, other serogroups, including O26, O111, O103, and O145, have the potential to cause the same spectrum of illness. In this study, 800 minced (ground) beef samples covering a large geographical region in Ireland were collected and tested for Escherichia coli (E. coli) O26 and E. coli O111 by conventional microbiological protocols. Two minced beef samples (0.25%) tested positive for E. coli O26, indicating fecal contamination. None of these isolates possessed verocytotoxin-encoding genes, (vt1/vt2 also known as stx1/stx2), the hemolysinencoding gene (hlyA), or the E. coli attachment-effacement (eae) gene, as determined by polymerase chain reaction (PCR). None of the beef samples analyzed contained E. coli O111. Although the E. coli O26 isolates were nonvirulent, the presence of these isolates in raw minced beef is an indication of fecal contamination and therefore potentially of public health significance.

Enterohemorrhagic Escherichia coli (EHEC)

Enterohaemorrhagic Escherichia coli has since the last 2 decades been known to cause severe and bloody diarrhoea as well as haemorrhagic colitis (HC) and haemorrhagic uraemic syndrome (HUS) especially among children. The importance of screening for EHEC among children and older patients with severe symptoms is apparent. Production of the verocytotoxins VT1 and VT2 are the main features of EHEC, and the VT types and mode of action during human infection is described. There are, however, other features adding to the pathogenicity. In this review we deal with the importance of properties such as fimbriae and adhesins as well as systems to meet the bacterial need for iron during infection. These factors are probably important for the establishment of EHEC in the gut and add to the bacterial virulence. It has now become evident that VT producing E. coli, irrespective of serogroup, might be human pathogens. We conclude that knowledge of the different possible virulence factors adds to the possibility of separating more virulent from less virulent isolates.

Effect of verocytotoxins (Shiga-like toxins) on human neutrophils in vitro

Neutrophil activation occurs in diarrhoea-associated HUS and correlates with disease severity, implying a role in pathogenesis. Verocytotoxin (Shiga-like toxin) has been shown to stimulate endothelium to release chemokines and express leukocyte adhesion molecules that would lead to indirect neutrophil-endothelial interaction. A direct action of verocytotoxin (VT) on neutrophils has been proposed, although in vitro studies of this are controversial. In this report we examine the effect of verocytotoxin-1 (Shiga-like toxin-1) (VT1) and verocytotoxin-2 (VT2) on human neutrophils in vitro with regard to priming, the release of superoxide and elastase, and chemotaxis. Neutrophils were incubated with VT1 or VT2 and superoxide and elastase release was measured over 120 and 45 minutes respectively. Priming was investigated by pre-treating the neutrophils with VT1 or VT2, exposing them to formyl-met-leu-phe (fMLP) or phorbol myristic acid (PMA) and measuring superoxide release. Neutrophil chemotaxis towards fMLP was assessed with and without pre-incubation with VT1 and VT2. We found that neither of the toxins induced superoxide or elastase release. Priming with VT1 significantly reduced superoxide release when neutrophils were stimulated with fMLP or PMA. VT2 priming gave a reduced superoxide release with PMA but not fMLP. Heat-inactivation of the toxins gave similar results. Pre-treatment of neutrophils with VT1 or VT2 did not affect chemotaxis towards fMLP after a 2-hour incubation period. In conclusion, VT1 and VT2 do not activate primed neutrophils in vitro. Nor do they affect chemotaxis towards fMLP. They may impair neutrophil priming.

Virulence genes in verocytotoxigenic Escherichia coli strains isolated from humans and cattle

Verocytotoxigenic Escherichia coli (VTEC) causing diarrhoea, haemorrhagic colitis and haemolytic-uremic syndrome usually have additional traits such as the adhesin intimin and a large plasmid that seems to increase virulence. There are, however, isolates of VTEC causing serious symptoms that do not harbour these traits. In the present study we have used PCR with primers detecting adhesin genes other than eaeA, namely fimA, papC, sfaD/sfaE and daaE. We have also used PCR to detect the genes hlyA and iutA that besides the plasmid-borne gene E-hly possibly support the bacterial access to iron. The aim of the study was to identify and compare the presence of virulence genes in VTEC isolates of human and cattle origin. The main finding was that the absence of E-hly might be compensated for by the gene iutA coding for aerobactin or hlyA coding for alpha-haemolysin as 94% of the human VTEC isolates had at least one of these genes. Interestingly, only 45% of VTEC isolated from cattle had any of these genes. We propose that this might be the reason for the relatively low incidence of symptomatic VTEC infections among humans in relation to the high number of VTEC among cattle.

Comparison of diversities of Escherichia coli O157 shed from a cohort of spring-born beef calves at pasture and in housing

A cohort of spring-born beef calves demonstrated limited genetic and phenotypic diversity of Escherichia coli O157 when kept in a state of isolation. Despite this, there was a difference in the pulsed-field gel electrophoresis and phage types of isolates shed by cattle at pasture compared with those shed by the same cattle when weaned and housed.

Isolation of shiga toxigenic Escherichia coli from raw beef in Palestine

Shiga toxigenic Escherichia coli (STEC) isolated from raw beef samples in northern Palestine during a 1-year period were characterized for virulence genes by a polymerase chain reaction (PCR) assay and screened for their antibiotic resistance. STEC was identified in 44 (14.7%) of 300 raw beef samples. Twelve (27.3%) of the STEC isolates were serotype O157. Nine of those were isolated during summer. The majority of STEC isolates (70.5%) harbored both stx1 and stx2 genes, while the others harbored either stx1 or stx2. High levels of resistance against different antimicrobial agents were detected. Resistance to at least three drugs was found in 55% of the isolates.

Serotypes and virulence genes of ovine non-O157 Shiga toxin-producing Escherichia coli in Switzerland

Sixty ovine STEC strains were examined with the aim (i) to serotype the strains, (ii) to characterize virulence factors, and (iii) to discuss possible associations between these factors and to assess the potential pathogenicity of these strains for humans. The 60 sorbitol-positive, non-O157 STEC strains belonged to 19 O:H serotypes, whereas 68% were of five serotypes (O87:H16, O91:H-, O103:H2, O128:H2, O176:H4). 52% belonged to serotypes reported in association with HUS. Five serotypes were not previously reported in sheep strains. Of the 47 strains encoding for stx1 variants, 57% were stx1c- and of the 45 encoding for stx2 variants, 80% were stx2d-positive. Eighty-two percent of the strains showed further putative virulence factors: 13% were eae-, 60% ehxA- and 67% saa-positive. The associations between harboring (i) eae and stx1, stx2, ehxA or no saa and (ii) saa and stx1c or stx2d were significant (P<0.05). The strains belonged to 27 seropathotypes (association between serotypes and virulence factors), but 57% belonged to only six and O91:H-stx1 stx2d saa and O128:H2 stx1c stx2d ehxA saa were the most common. Seven of the eight intimin-positive strains harbored eae. Four strains of serotype O103:H2 and O121:H10 harboring stx2, eae and ehxA showed virulence factors typical for strains associated with severe human disease. However, according to the virulence factors, the majority of the ovine non-O157 STEC strains are assumed low-virulence variants. Nevertheless, as long as the contribution and interaction of these factors in milder disease remains unclear P, a certain risk for humans cannot be excluded.

Isolation of a rare Escherichia coli O157:H7 strain from farm animals in Greece

A strain of Escherichia coli O157:H7 was isolated from goat faeces during a surveillance study on the prevalence of this serotype of E. coli in farm animals in Greece. Three hundred and fifty one faecal samples were collected from goat, sheep and cattle breeding farms in the area of Epirus, Northwestern Greece. The E. coli O157:H7 isolate was nonsorbitol-fermenter, produced only VT2 and showed a beta-glucuronidase positive activity, a rather unusual biochemical feature for the E. coli O157:H7 serotype. No other strain of E. coli O157:H7 was isolated from the faecal samples of the rest farm animals examined, thus the overall prevalence of animal carriage was found to be 0.2%. The findings also indicate that goats can be a reservoir of E. coli O157:H7 and goat milk, dairy products and meat may serve as a vehicle for the pathogen transmission to humans.

Isolation of Escherichia coli O157 from human and bovine faeces in the Urbino area, Italy

We examined 476 faecal samples from subjects aged from 0 to >60 years, 283 with diarrhoea and 193 with illnesses involving other sites or clinically healthy, and 154 samples of faeces of healthy cattle, in order to define the diffusion of E. coli O157 in the Urbino area. The samples were seeded by both direct streaking onto cefixime tellurite sorbitol Mac Conkey agar (CT-SMAC) and previous enrichment in cefixime tellurite tryptone soya broth for human specimens and in cefixime vancomicin tryptone soya broth for bovine samples. The strains of E. coli O157 were characterized by verocytotoxin and adhesin eae genes detection. We isolated one strain of E. coli O157 (0.2%) from a man 68 year old who had bloody diarrhoea, and one strain (0.64%) from a weaned calf. Both isolates carried the adhesin eae gene, but only the bovine strain was VT2+. The study shows a low diffusion of E. coli O157 in the Urbino area, confirming the epidemiological data on the national territory.

Detection and characterization of verocytotoxin-producing Escherichia coli by automated 5' nuclease PCR assay

In recent years increased attention has been focused on infections caused by isolates of verocytotoxin-producing Escherichia coli (VTEC) serotypes other than O157. These non-O157 VTEC isolates are commonly present in food and food production animals. Easy detection, isolation, and characterization of non-O157 VTEC isolates are essential for improving our knowledge of these organisms. In the present study, we detected VTEC isolates in bovine fecal samples by a duplex 5' nuclease PCR assay (real-time PCR) that targets vtx1 and vtx2. VTEC isolates were obtained by colony replication by use of hydrophobic-grid membrane filters and DNA probe hybridization. Furthermore, we have developed 5' nuclease PCR assays for the detection of virulence factors typically present in VTEC isolates, including subtypes of three genes of the locus of enterocyte effacement (LEE) pathogenicity island. The 22 assays included assays for the detection of verocytotoxin genes (vtx1, vtx2), pO157-associated genes (ehxA, katP, espP, and etpD), a recently identified adhesin (saa), intimin (eae, all variants), seven subtypes of eae, four subtypes of tir, and three subtypes of espD. A number of reference strains (VTEC and enteropathogenic E. coli strains) and VTEC strains isolated from calves were tested to validate the PCR assays. The expected virulence profiles were detected for all reference strains. In addition, new information on the subtypes of LEE genes was obtained. For reference strains as well as bovine isolates, a consistent relationship between subtypes of the LEE genes was found, so that a total of seven different combinations of these were recognized (corresponding to the seven subtypes of eae). Isolates with 15 different serogroup-virulence profiles were isolated from 16 calves. Among these, 53% harbored LEE and 73% harbored factors carried by the large virulence plasmid. One LEE-negative isolate had the gene for the adhesin Saa. The most common virulence profile among the bovine isolates was vtx1, eae-zeta, tir-alpha, ehxA, and espP. This panel of assays offers an easy method for the extensive characterization of VTEC isolates.

Essential role for verotoxin in sustained stress-activated protein kinase and nuclear factor kappa B signaling, stimulated by Escherichia coli O157:H7 in Vero cells

The effects of Escherichia coli O157:H7 (strains E30480 and PM601) and the associated verotoxins (VTs), VT1 and VT2, on stress-activated protein kinase and nuclear factor kappa B (NF-kappaB) signaling were investigated with Vero cells, which are extremely sensitive to the cytotoxic effects of E. coli O157:H7 in vitro. Cell-free supernatants prepared from E30480 and PM601 cultures and purified VT1 and VT2 stimulated a strong and prolonged (>4-h) activation of both c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase. However, JNK activity stimulated in response to E30480 supernatants was substantially reduced following pretreatment with anti-VT1 and anti-VT2 antibodies, while a VT1 and VT2 gene knockout mutant of PM601 was unable to stimulate JNK activity. E30480 supernatants also caused a sustained activation of NF-kappaB DNA binding, degradation of inhibitory kappa B alpha (IkappaBalpha), and an increase in inhibitory kappa B kinase alpha activity, although PM601 supernatants and VT1 and VT2 had no effect. However, preincubation with VTs prolonged the transient activation of NF-kappaB and IkappaBalpha degradation stimulated by either tumor necrosis factor alpha or interleukin 1beta, while preincubation with anti-VT antibodies prevented the prolonged loss of IkappaBalpha and partially reduced DNA binding in response to E30480 supernatants. These results strongly suggest that in Vero cells, VT plays an essential role in sustained JNK and NF-kappaB signaling in response to E. coli O157:H7 and that this action may underpin their cell-selective cytotoxic effects. These studies also suggest that another component released by strain E30480 contributes to the early activation of JNK and NF-kappaB.

A quartz crystal microbalance method for rapid detection and differentiation of shiga toxins by applying a monoalkyl globobioside as the toxin ligand

A simple globobiosyl (Gb2) ceramide mimic carrying a monoalkyl chain (C18) was applied for a monolayer Langmuir-Blodgett (L-B) technique to detect Shiga toxins (Stxs) by a quartz crystal microbalance (QCM) method. The artificial glycolipid, synthesized from penta-O-acetyl-D-galactopyranose via a conventional glycosidation pathway, was developed at the air-water surface for the formation of the monolayer film. Then, the film was transferred onto a QCM cell surface modified with alkanethiols. Upon the addition of each of Stx-1 and Stx-2, the decrease of frequency reached saturation within 45 min at a few nanogram order per quartz cell. Binding constants (Ka) estimated for each of Stx-1 and Stx-2 showed little difference between the two toxins. On the other hand, in the presence of an artificial acrylamido Gb2 copolymer as a competitive inhibitor, the two toxins showed a large difference in the binding behavior to the L-B monolayer.

Detection of verocytotoxin bound to circulating polymorphonuclear leukocytes of patients with hemolytic uremic syndrome

The epidemic form of hemolytic uremic syndrome (HUS) is the most common cause of acute renal failure in children and is characterized by a prodromal phase of sometimes bloody diarrhea. The role of verocytotoxin (VT)-producing Escherichia coli has been strongly implicated. Although antibodies against VT have been detected in the serum of patients with HUS, VT itself has never been detected in circulating blood. In this study, VT-2 was detected in the systemic circulation in 9 of 10 patients with the epidemic form of HUS. In those cases, VT-2 was bound exclusively to polymorphonuclear leukocytes (PMN). The detection of VT-2 bound to PMN was associated with the presence of diarrhea at the time the blood samples were obtained. The one patient for whom VT was not detected presented with atypical HUS. For 5 of the 10 patients with HUS who were studied, the time course of VT binding was analyzed; binding decreased in four patients. The finding of VT bound to PMN in the systemic circulation of patients with HUS is important for a clearer understanding of the pathogenesis of HUS and suggests new approaches for treatment in the future.

Virulence genotypes and serotypes of verotoxigenic Escherichia coli isolated from cattle and foods in Argentina. Importance in public health

Virulence factors of Verotoxin-producing Escherichia coli (VTEC) strains isolated from hamburgers and ground beef were studied in Argentina by PCR. Their virulence profiles were correlated with those corresponding to strains isolated from calves and adult cattle. Most virulent profiles (VTs+ eae+ Mp+) were present in E. coli from healthy and diarrheic calves corresponding to O5:H-, O5:H27, O20:H?, O26:H11, O38:H?, O103:H-, O103:H2, O111:H-, O118:H16, O165:H-serotypes. The presence of the eae gene was significantly more frequent among VTEC strains isolated from calves (20/26; 76%) than from adult cattle (1/39; 2.5%) (p < 0.005). VT2+ eae- E. coli was prevalent in foods and adult cattle at slaughterhouse. The prevalence of the eae gene was similar between VTEC strains isolated from meat (0/21) and adult cattle (1/39; 2.5%) which constitutes the main population processed at slaughterhouses in Argentina. Serotyping showed that VTEC strains were distributed among 31 serotypes, some of which (O20:H19, O91:H21, O113:H21, O116:H21, O117:H7, O171:H2, OX3:H21) were shared between bovine and food strains. These O serogroups have been isolated from cases of haemorrhagic colitis (HC) and haemolyticuraemic syndrome (HUS) in humans in several continental European countries. This study confirms the role of cattle as a reservoir of many VTEC serotypes other than O157:H7 and represents a base for future diagnostic, prevention and control strategies of EHEC in this country. In addition, this study affirms the advantages of PCR-based screening of E. coli isolates given the finding of so many verotoxin-producing strains.

Effects of interaction between Escherichia coli verotoxin and lipopolysaccharide on cytokine induction and lethality in mice

In Escherichia coli 0157 infections, verotoxins (VT) play a critical role in causing the disease, although other factors such as lipopolysaccharide (LPS) and inflammatory cytokines may affect the progression and course of the disease. The present study examined the roles of VT and LPS in induction of serum cytokines and lethality in mice. LD50 of VT2 (13 ng) was c. 10(4)-fold smaller than that of LPS (400 microg). Although the lethal toxicity of these toxins was examined in several experimental conditions, such as VT2 (5, 10, 20, 40 ng/mouse) alone or in combination with LPS (100 microg/mouse) at various times (-2 days to +2 days), no evidence of synergy was observed. VT2 did not augment LPS-induced tumour necrosis factor-alpha (TNF-alpha) or interleukin-6 production, and conversely suppressed TNF-alpha production when it was injected 2 days before LPS challenge. The data failed to indicate either synergic or additive effects of VT and LPS on cytokine production or lethality in mice. In contrast, antagonistic interactions were clearly observed in cytokine production in certain conditions. The results suggested that these toxins may be co-operatively involvedin the pathology of VT-related diseases, but not through synergic interactions.

Disorders in the immune responses of T- and B-cells in mice administered intravenous verotoxin 2

To obtain a better insight into the pathogenesis of verotoxin-producing Escherichia coli (VTEC)-associated diseases, we explored the effect of verotoxin 2 (VT2) on the immune response in mice. The distribution of lymphocyte phenotypes and the lymphocyte immune response were examined after intravenous administration of VT2 to mice. Among the peripheral lymphocytes and splenocytes of 4-week-old C57BL/6 mice, there was first of all a decrease in T-cells, which began 24 h after intravenous administration of VT2 (50 ng/kg, lethal dose). The CD4+ cell subpopulations of the peripheral blood and spleen were significantly decreased at 24 h, while the B220+ splenocyte subpopulation was markedly decreased at 45 h after VT2 administration. In the thymus, a decrease in CD4+CD8+ cells was predominantly observed near death. Interestingly, in E. coli lipopolysaccharide (LPS)-responder mouse strains (C57BL/6 and C3H/HeN) cotreated with LPS, the susceptibility to VT2 was enhanced, and the increase in B220+ cells induced by LPS alone was suppressed. Furthermore, splenocytes from C57BL/6 mice treated with VT2 (50 ng/kg) 6-24 h earlier reduced LPS-induced proliferative responses to 50-52% of that in control cells, indicating that the effect of VT2 on the immunoresponse seen in vivo may be negatively exerted on the proliferation of the cells. In addition, the number of splenocytes that produced anti-sheep red blood cell antibody was decreased in mice treated with VT2. These results suggest that VTEC infection may eliminate CD4+ and CD8+ T-cells and B-cells by affecting their survival and proliferative responses, leading to reduced antibody production.

Application of polymer-embedded proteins to fabrication of DNA array

A plasma-polymerized film (PPF) of hexamethyldisiloxane [HMDS; (CH(3))(3)SiOSi(CH(3))(3)] was used to immobilize streptavidin on a glass substrate. Another layer of HMDS-PPF was also applied to the protein, which was first adsorbed to an underlayer of the same kind of film. As the result, the streptavidin was "embedded" between the two layers of HMDS, whereby biotinylated molecules could be efficiently captured. The second layer of approximately 30 to 45 A PPF was sufficient to allow the binding of biotinylated molecules, whereas thicknesses of >90 A significantly hindered the streptavidin-biotin interactions. Fluorescence analysis revealed that the absence of an HMDS plasma-polymer (HMDS-PP) layer on either side of the streptavidin film resulted in a decrease in biotin binding. This immobilization technique was used to bind biotinylated oligonucleotides in sequence-specific DNA-DNA interactions. The hydrophobic properties of the plasma-polymerized HMDS thin film acted to minimize nonspecific DNA binding to the glass substrate. A DNA array was fabricated using this procedure and showed greatly decreased nonspecific DNA binding compared with a poly-L-lysine coated substrate.

Bcl-2 antiapoptotic protein mediates verotoxin II-induced cell death: possible association between bcl-2 and tissue failure by E. coli O157:H7

Verotoxin II (VTII: or Shiga-like toxin 2) is a key factor for Escherichia coli O157:H7-induced multiple tissue failure and contains a pentameric sequence (NWGRI) similar to the Bcl-2 homolog domain, BH1. In the current study, we demonstrate that VTII, but not VTI, interacts with Bcl-2 through each BH1 domain pentameric sequence (NWGRI) and that the VTII/Bcl-2 complex is necessary for cell-death induction in target cells. VTII translocates to mitochondria and induces cell death only when target cells are expressing Bcl-2. In addition, interruption of VTII-Bcl-2 complex formation by a pentameric BH1 synthetic peptide suppresses VTII-induced cell death. In the present article, we propose that Bcl-2 mediates VTII-induced target cell death by the interaction with each pentameric sequence of BH1 domain.

Rapid SLT gene detection on polyethylene-coacrylic acid film without molecular labels or surface-fouling agents

The commercially available copolymer of 10 mol% acrylic acid and polyethylene is easily formed into a nonfluorescing, non-polynucleotide-adsorbing film. The film has surface carboxylate functions whose concentration can be increased by heating to 80 degrees C in 30% NaOH. The carboxylate groups will react at pH approximately 7 with commercially available, oligo-DNA, 2-8 ng/microl, that has been synthesized with a C(12)-alkylamino tail on the 5'-end. The reaction is mediated with water-soluble carbodiimide reagent and is assumed to result in a primary amide bond between the polymer film and the modified oligo-DNA. The tethered oligo-DNA retains its hybridization activity, and its surface concentration is sufficient to permit qualitative, labelless detection of hybridized target by fluorescence after brief staining with ethidium bromide. The film is used to detect Shiga-like toxin gene II (SLT-II) from Escherichia coli O157:H7 after asymmetric, capillary, PCR amplification, and a 4-h hybridization. Captured target may be removed from the film using distilled water, after which the film can be used again without noticeable loss of activity. The method provides relatively rapid detection of PCR amplimers without having to use molecular labels, or surface-fouling agents.

Macrolides and clindamycin suppress the release of Shiga-like toxins from Escherichia coli O157:H7 in vitro

We investigated the effects of antimicrobial agents fosfomycin (FOS), cefdinir (CDIN), levofloxacin (LEVX), rokitamycin (ROK), roxithromycin (ROX), and clindamycin (CLI) on the release of Shiga-like toxins (SLTs) by enterohaemorrhagic Escherichia coli (EHEC). EHEC was cultured for 14 h in the presence of ROX, ROK or CLI at sub-minimum inhibitory concentrations (subMICs) of 1.56-6.25 mg/l, followed by assay of the level of SLTs in the supernatants using cytotoxicity assay and reversed passive latex agglutination method. Exposure to ROX, ROK or CLI reduced the amount of released SLTs compared with untreated control cultures (P<0.05). These agents however, did not decrease the number of viable EHEC, indicating the importance of bactericidal agents. When the bacteria was exposed to CDIN, FOS or LEVX, the level of SLTs in the culture supernatant increased with the destruction of bacterial cells in the order of CDIN, FOS, LEVX. When 0.5 mg/l of LEVX was added to cultures with or without pretreatment using ROX, ROK, or CLI, the release of SLTs was reduced by this pretreatment (P<0.05). These results may have clinical implications for the treatment of EHEC infection.

A mutant Shiga-like toxin IIe bound to its receptor Gb(3): structure of a group II Shiga-like toxin with altered binding specificity

BACKGROUND

Shiga-like toxins (SLTs) are produced by the pathogenic strains of Escherichia coli that cause hemorrhagic colitis and hemolytic uremic syndrome. These diseases in humans are generally associated with group II family members (SLT-II and SLT-IIc), whereas SLT-IIe (pig edema toxin) is central to edema disease of swine. The pentameric B-subunit component of the majority of family members binds to the cell-surface glycolipid globotriaosyl ceramide (Gb(3)), but globotetraosyl ceramide (Gb(4)) is the preferred receptor for SLT-IIe. A double-mutant of the SLT-IIe B subunit that reverses two sequence differences from SLT-II (GT3; Gln65-->Glu, Lys67-->Gln, SLT-I numbering) has been shown to bind more strongly to Gb(3) than to Gb(4).

RESULTS

To understand the molecular basis of receptor binding and specificity, we have determined the structure of the GT3 mutant B pentamer, both in complex with a Gb(3) analogue (2.0 A resolution; R = 0.155, R(free) = 0.194) and in its native form (2.35 A resolution; R = 0.187, R(free) = 0.232).

CONCLUSIONS

These are the first structures of a member of the medically important group II Shiga-like toxins to be reported. The structures confirm the previous observation of multiple binding sites on each SLT monomer, although binding site 3 is not occupied in the GT3 structure. Analysis of the binding properties of mutants suggests that site 3 is a secondary Gb(4)-binding site. The two mutated residues are located appropriately to interact with the extra betaGalNAc residue on Gb(4). Differences in the binding sites provide a molecular basis for understanding the tissue specificities and pathogenic mechanisms of members of the SLT family.

Development and evaluation of a PCR-microplate capture hybridization method for direct detection of verotoxigenic Escherichia coli strains in artificially contaminated food samples

For the purpose of detecting, directly in food, verotoxigenic Escherichia coli, a microplate hybridization method for the detection of PCR products from the SLT I and SLT II genes, was developed and evaluated. Two pairs of primers and two probes, specific for the SLT I gene and for the SLT II gene, were designed and tested. For the strains containing both genes, two PCR products of different molecular weights were obtained, whereas when only one gene was present only one fragment resulted from PCR. The use of the biotin-labeled probes allowed the immobilization of the PCR products in the microtiter plate wells and by this means their detection was possible using an ELISA-based technique. Forty artificially contaminated and fifty naturally contaminated food samples were analyzed by using the PCR-microplate hybridization technique developed in this study. All the artificially contaminated food samples were positive, independently of the number of cells inoculated before the enrichment step, whereas the naturally contaminated food samples were all negative.

Detection of Escherichia coli O157:H7 in heifers' faecal samples using an automated immunoconcentration system

Pre-treatment of a 5-h enrichment culture with an automated immunoconcentration (ICE) system greatly improved the isolation of Escherichia coli O157:H7 from spiked heifer faecal samples. Enrichment samples plated directly onto sorbitol MacConkey agar (SMAC) and SMAC agar supplemented with cefixime and potassium tellurite (CT-SMAC) showed recovery rates of 8% and 56%, respectively. However, after ICE treatment, E. coli O157:H7 was recovered from 92% of the samples on SMAC and 100% on CT-SMAC. Immunoconcentration analysis of heifers' faecal samples collected from a slaughter-house in France, during March to June 1998, showed that 1% (three of 300) was positive for E. coli O157:H7. Phenotypic and genotypic analysis showed that all three isolates carried both the O157 and H7 antigens, did not ferment sorbitol or had beta-glucuronidase activity and carried trait virulence factors for E. coli O157:H7 (uidA allele, eaeA and pO157 plasmid). However, only one strain was toxigenic and this strain produced a single toxin, namely verotoxin 2.

Chromosome of the enterohemorrhagic Escherichia coli O157:H7; comparative analysis with K-12 MG1655 revealed the acquisition of a large amount of foreign DNAs

A complete Xba I and Bln I cleavage map was constructed for the chromosome of an enterohemorrhagic Escherichia coli (EHEC) O157:H7 strain isolated from an outbreak in Sakai City, Japan, in 1996. A comparative chromosome analysis with E. coli K-12 strain MG1655 was made. The EHEC chromosome was approximately 5600 kb in length, 1 Mb larger than that of MG1655. Despite the marked difference in chromosome length, the location and direction of seven rRNA operons of the EHEC strain were similar to those for MG1655. Overall organization of genes common in both strains is also highly conserved. Chromosome expansion was observed throughout the EHEC chromosome, albeit in an uneven manner. A large portion of the chromosome enlargement was observed in the region surrounding the replication terminus, particularly in a segment containing the terA locus. Sample sequencing of 3627 random shotgun clones suggested the presence of approximately 1550 kb strain-specific DNAs on the EHEC chromosome, most of which are likely to be of foreign origin.

Inhibition of neutrophil apoptosis by verotoxin 2 derived from Escherichia coli O157:H7

In order to evaluate the pathological role of verotoxin 2 (VT2), we investigated the effects of VT2 on neutrophil apoptosis in vitro. The results showed that VT2 caused a significant delay in spontaneous neutrophil apoptosis and that the effect was abrogated by a protein kinase C inhibitor. These data indicate that longer survival of neutrophils may aggravate neutrophil-mediated tissue damage in VT2-associated diseases.

Chemotherapy for enterohemorrhagic Escherichia coli O157:H infection in a mouse model

The aim of this study is to evaluate the therapeutic effect of the antimicrobial agents, fosfomycin (FOM), minocycline (MINO), kanamycin (KM) and norfloxacin (NFLX) in the enterohemorrhagic Escherichia coli (EHEC) infected mouse model which we established previously (Infect. Immun. 62 (1994) 3447-3453). Each of the antimicrobial agents, 1/16 LD(50), was given to the mice per os (p.o. ) or intraperitoneally (i.p.) for 3 days after bacterial inoculation and then we observed their mortality rate for 2 weeks. The mortality rates of mice administered with MINO (p.o./i.p.), KM (p.o.), NFLX (p. o./i.p.) were significantly lower than those of the control group. Both the bacterial number and VT2c level in the feces of the FOM group were lower than those of the NFLX group on day 1, but reversed on day 3. In an in vitro experiment, each of the four drugs in combination with mitomycin C (MMC) caused a more significant decrease in the bacterial number than sole MMC, and they consequently indicated the suppressive effect on the release of VT2c.

Complete nucleotide sequence of the prophage VT2-Sakai carrying the verotoxin 2 genes of the enterohemorrhagic Escherichia coli O157:H7 derived from the Sakai outbreak

The enterohemorrhagic Escherichia coli (EHEC) O157:H7 strain RIMD 0509952, derived from an outbreak in Sakai city, Japan, in 1996, produces two kinds of verotoxins, VT1 and VT2, encoded by the stx1 and stx2 genes. In the EHEC strains, as well as in other VT-producing E. coli strains, the toxins are encoded by lysogenic bacteriophages. The EHEC O157:H7 strain RIMD 0509952 did not produce plaque-forming phage particles upon inducing treatments. We have determined the complete nucleotide sequence of a prophage, VT2-Sakai, carrying the stx2A and stx2B genes on the chromosome, and presumed the putative functions of the encoded proteins and the cis-acting DNA elements based on sequence homology data. To our surprise, the sequences in the regions of VT2-Sakai corresponding to the early gene regulators and replication proteins, and the DNA sequences recognized by the regulators share very limited homology to those of the VT2-encoding 933W phage carried by the EHEC O157:H7 strain EDL933 reported by Plunkett et al. (J. Bacteriol., p1767-1778, 181, 1999), although the sequences corresponding to the structural components are almost identical. These data suggest that these two phages were derived from a common ancestral phage and that either or both of them underwent multiple genetic rearrangements. An IS629 insertion was found downstream of the stx2B gene and upstream of the lysis gene S, and this might be responsible for the absence of plaque-forming activity in the lysate obtained after inducing treatments.

[Colibacillosis in swine: proof of vaccine efficacy]

The damage caused in the economy and animal sanity by the porcine colibacilosis are significant and they deserve the investigation of preventive measures that give answers to the producers. Existing at the present time approximately 21,000 pigs in Corrientes and 110,000 in Chaco provinces of Argentine, the losses for diarrhea that exterminate whole litters, acquire relevance, specially if they can be prevented or cured. For that reason, having 21 strains of enteropathogenic and verocitotoxigenic E. coli (ETEC/VTEC) isolated from pigs of the North East of Argentine, that were recognized by PCR, two were selected, containing the genes for STIa, STIb, LTI, VT2e (SLT-IIv) and F4 (K88). They were spread on nutrient agar and Minca medium, to obtain the suspension in PBS, which was inactivated with formol. After the sterility and innocuity controls, it was diluted to a 12 x 10(8) concentration to make the mouse protection test in 20 mice, of 18-20 g, inoculating the vaccine the days 1, 4, 7 and 10, by the intraperitoneal route, doses of 0.25 ml each one. The day 21 after beginning the test the animals were challenged with 50 LD50, and a protection of 85% was obtained. To determine the LD50, we prepared a suspension in physiologic solution, corresponding to Mac Farland's tube No 10, making dilutions from 10(-1) to 10(-5) and applying the statistical method of Reed and Muench. These first results encourage us to continue working after a prophylactic measure that were effective, potent and elaborated with strains of this area.

Molecular characterisation of verocytotoxin-producing Escherichia coli of serogroup O111 from different countries

A collection of epidemiologically unrelated verocytotoxin (VT)-producing Escherichia coli (VTEC) strains of serogroup O111 isolated from human patients and cattle with diarrhoeal disease in five different countries were characterised by determination of their VT genotypes, the presence of other virulence factors such as the intimin-coding eae gene and the enterohaemorrhagic E. coli (EHEC) plasmid, and their antibiotic susceptibility patterns. The genetic relatedness among isolates was evaluated by genomic DNA fingerprinting techniques such as restriction fragment length polymorphism analysis of ribosomal RNA genes (ribotyping) and pulsed-field gel electrophoresis. The results indicated that the VTEC O111 examined belong to two distinct clonal lineages. The first group was constituted mainly of non-motile, eae-positive, EHEC plasmid-positive isolates from both man and cattle. The second lineage was represented by an O111:H2 epidemic strain, isolated during an outbreak of haemolytic uraemic syndrome in France and exhibiting an unusual combination of virulence factors: VT production and aggregative adhesion to HEp-2 cells associated with an enteroaggregative E. coli (EAEC) plasmid.

A reverse-sandwich enzyme-linked immunosorbent assay for verocytotoxin 1 and 2 antibodies in human and bovine sera

A reverse-sandwich enzyme-linked immunosorbent assay (ELISA), in which an antibody is sandwiched by antigens, was established for the titration of antibodies to verocytotoxins (VT) in human and animal sera. This assay has two advantages over a conventional indirect ELISA: (i) higher specificity and sensitivity and (ii) the ability to comparably titrate antibodies from different species. The VT1 (Shiga-like toxin 1) antibody-positive rates were 5% in 202 normal adult humans and 99% in 93 normal cattle at a dairy farm. This ELISA is most suitable for seroepidemiologic studies of infections with VT-producing Escherichia coli in humans and various animal species.

Synthesis of an artificial glycoconjugate polymer carrying Pk-antigenic trisaccharide and its potent neutralization activity against Shiga-like toxin

Fluorescence-labeled glycoconjugate polymers carrying carbohydrate segments of a globotriaosyl ceramide (Gb3) were synthesized and subjected to biological assays using Escherichia coli O-157 strains and Shiga-like toxins (Stx-I and Stx-II). For the fluorescence labeling, a new polymerizable fluorescent monomer with a TBMB carbonyl chromophore (Ex. 325 nm, Em. 410 nm) was designed. A glycosyl monomer of the trisaccharide segment of Gb3 was prepared from p-nitrophenyl beta-lactoside and copolymerized with acrylamide and the fluorescent monomer to prepare a fluorescence-labeled glycoconjugate copolymer carrying [alpha-D-galactopyranosyl-(1-->4)-beta-D-galactopyranosyl]-(1-->4)-beta- D-glucopyranoside. The polymer showed potent neutralization activity against Stx-I and also binding activity onto E. coli O-157 strains.

Prevalence of virulence factors of Escherichia coli strains isolated from diarrheic and healthy piglets after weaning

This study determined the prevalence of F4, F5, F6, F17 and F41 fimbriae and the genes for FedA (F18 fimbriae), LT and ST enterotoxins, and Shiga toxins Stx1, Stx2 and Stx2e among E. coli isolated from 372 weaned pigs with diarrhea and 46 healthy pigs of the same age. Agglutination tests showed that most isolates were negative for all five fimbrial antigens. The F4 antigen was found in 71 (19.1%) and the F5, F6, or F41 antigen was detected in 6.4% of isolates from diseased pigs. Genes for the F18 fimbriae were detected in 10 (2.7%) strains from diarrheic pigs and in 1 of 46 isolates from healthy pigs. Most isolates (213, 57.3%) from pigs with diarrhea were positive for LTI only or for LTI and STI or Stx2e toxin genes. Fifteen strains (13.7%) possessed only the STI or STII toxin genes. All F4-positive bacteria had genes for LTI or LTI and STI, whereas F18-positive isolates had genes for LTI, LTI/STI, or LTI/Stx2e. Of the strains isolated from diseased pigs, 264 (71.0%) were negative for the fimbrial antigens (genes) examined in this study. The fimbria-negative isolates frequently possessed genetic determinants for LTI (118, 31.7%) or for STII (16, 4.3%) enterotoxins.

Haemolytic-uraemic syndrome caused by vero toxin-producing Escherichia coli serotype Rough: K-: H49

The first case of haemolytic-uraemic syndrome (HUS) caused by Vero toxin-producing Escherichia coli (VTEC) which belonged to a novel serotype, Rough: K-: H49, is reported. The case was initially diagnosed as nephropathia epidemica caused by Puumala virus, but the subsequent diagnosis of HUS caused by VTEC was made after bacteriological investigation. The strain isolated fermented sorbitol produced VT2 toxin but not enterohaemolysin, nor did it carry the eaeA gene. In VTEC strains, the O antigen, the eaeA gene and enterohaemolysin production have been characterized as virulence-associated factors and believed to have an effect on pathogenesis of these strains to cause haemorrhagic colitis or HUS. The findings of this study demonstrate that there is a need for further studies to evaluate the pathogenetic mechanism of VTEC and need for easy diagnostic methods exploiting other properties than O157 antigen and non-fermentation of sorbitol to find all VTEC in human infections.

In vitro assessment of a chemically synthesized Shiga toxin receptor analog attached to chromosorb P (Synsorb Pk) as a specific absorbing agent of Shiga toxin 1 and 2

A synthetic analog of Shiga toxin (Stx) receptor (Synsorb Pk) was quantitatively assessed to determine whether it can protect human renal adenocarcinoma cells (ACHN cells) from the cytotoxicity of Stx1 and Stx2 by coincubation experiments. Coincubation of 100 and 20 ng of Stxl and Stx2 with 50 mg of Synsorb Pk for 1 hr at 37 C in 1 ml of Eagle's Minimum Essential Medium supplemented with 1% (v/v) non-essential amino acid and 10% (v/v) fetal calf serum protected 50% of the cells from the cytotoxic effect. Chromosorb P, an inert matrix control, did not absorb the Stxs at all. Heat-treatment (boiled for 10 min) to Synsorb Pk caused a 50% decrease in Stx2-binding activity, but did not effect the Stx1 binding. Further, Stxs bound to Synsorb Pk could be demonstrated. When 20 mg of Synsorb Pk was coincubated for 30 min at 37 C in 1 ml of phosphate-buffered saline with 1 and 10 ng or more of Stx1 or Stx2, respectively, the toxins could be detected on the surface when the bound toxins on Synsorb Pk were used as the solid phase in enzyme immunoassay. The amount of 100 ng/ml of both Stxl and Stx2 appeared to saturate 20 mg/ml of Synsorb Pk after coincubating for 30 min at 37 C. While assessing the Stxs' binding activity to Synsorb Pk, it was demonstrated that Stxl had a higher affinity to Pk trisaccharide than Stx2. These observations provide useful information on the effectiveness of Synsorb Pk to trap and eliminate free Stxs produced in the gut of patients infected by Stx-producing Escherichia coli, and to prevent the progression of hemorrhagic colitis to hemolytic uremic syndrome.