Translocated intimin receptors (Tir) of Shiga-toxigenic Escherichia coli isolates belonging to serogroups O26, O111, and O157 react with sera from patients with hemolytic-uremic syndrome and exhibit marked sequence heterogeneity

Multilocus-based phylogenetic analysis of extended-spectrum beta-lactamase Escherichia coli O157:H7 uncovers related strains between agriculture and nearby water sources

This study aimed to uncover related strains of extended-spectrum beta-lactamase Escherichia coli O157:H7 between agricultural matrices (soil, manure and irrigation water) and nearby water sources using multilocus-based phylogenetic analysis. Resistant and nonresistant E. coli O157:H7 were isolated, identified and characterised using standard microbiological methods. The results showed that soil samples had a high prevalence of E. coli O157:H7 (31.73%) and ESBL-producing E. coli O157:H7 (22.11%). Multilocus sequencing typing (MLST) analysis revealed that all ESBL-producing E. coli O157:H7 were identified as ST11. Phylogenetic analysis of E. coli O157:H7 indicated that irrigation water might be a reservoir for E. coli O157:H7. For antibiotic-resistant genes (ARG), the most common was bla_TEM in 85% (n = 34), followed by bla_OXA in 70% (n = 28), bla_NDM and sul1 30% (n = 12) and lastly mcr-1, which was only found in one soil isolate. The results showed that ESBL-producing E. coli O157:H7 isolates were intermixed in three clades, indicating close relatedness between isolated strains from different matrices.

Immunogenicity of the nanovaccine containing intimin recombinant protein in the BALB/c mice

Purpose

Escherichia coli O157:H7 is one of the most important pathogens which create hemorrhagic colitis and hemolytic uremic syndrome in human. It is one of the most prevalent causes of diarrhea leading to death of many people every year. The first diagnosed gene in the locus of enterocyte effacement pathogenicity island is eae gene. The product of this gene is a binding protein called intimin belonging to the group of external membrane proteins regarded as a good stimulants of the immune system. Chitosan with its lipophilic property is an environmentally friendly agent able to return to the environment.

Materials and Methods

Intimin recombinant protein was expressed in pET28a vector with eae gene and purification was performed using Ni-NTA and finally the recombinant protein was approved through western blotting. This protein was encapsulated using chitosan nanoparticles and the size of nanoparticles was measured by Zetasizer. Intimin encapsulated was prescribed for three sessions among three groups of oral, injection, and oral-injection using Chitosan nanoparticles. Challenge was performed for all three groups with 10⁸E. coli O157:H7 bacteria.

Results

Intimin produced by chitosan nanoparticles improves immunological responses through the adjuvant nature of chitosan nanoparticles. Chitosan may be used as a carrier for transportation of the prescribed vaccine. Among the mice, encapsulated intimin could be able to provide suitable titers of IgG and IgA by the aid of chitosan nanoparticles. Results of mice challenge showed that decreased the bacterial shedding significantly.

Conclusion

Results showed that the chitosan nanovaccine with intimin protein may be used as a suitable candidate vaccine against E. coli O157:H7.

Role of climate in the spread of shiga toxin-producing Escherichia coli infection among children

Haemolytic-uraemic syndrome (HUS) is a rare disease mainly affecting children that develops as a complication of shiga toxin-producing Escherichia coli (STEC) infection. It is characterised by acute kidney injury, platelet consumption and mechanical destruction of red blood cells (haemolysis). In order to test the working hypothesis that the spread of the infection is influenced by specific climatic conditions, we analysed all of the identified cases of infection occurring between June 2010 and December 2013 in four provinces of Lombardy, Italy (Milano, Monza Brianza, Varese and Brescia), in which a STEC surveillance system has been developed as part of a preventive programme. In the selected provinces, we recorded in few days a great number of cases and clusters which are unrelated for spatially distant or for the disease are caused by different STEC serotypes. In order to investigate a common factor that favoured the onset of infection, we have analysed in detail the weather conditions of the areas. The daily series of temperature, rain and relative humidity were studied to show the common climate peculiarities whilst the correlation coefficient and the principal component analysis (PCA) were used to point out the meteorological variable, maximum temperature, as the principal climate element in the onset of the infection. The use of distributed lag non-linear models (DLNM) and the climate indices characterising heat waves (HWs) has allowed to identify the weather conditions associated with STEC infection. The study highlighted a close temporal correlation between STEC infection in children and the number, duration and frequency of heat waves. In particular, if the maximum temperature is greater than 90th percentile, days classified as very hot, for 3 or more consecutive days, the risk of infection is increasing.

Virulence characterization and molecular subtyping of typical and atypical Escherichia coli O157:H7 and O157:H(-) isolated from fecal samples and beef carcasses in Mexico

The objective of the study was to characterize virulence genes and subtype Escherichia coli O157:H7 and O157:H( 2 ) isolates obtained from a vertically integrated feedlot slaughter plant in Mexico. A total of 1,695 samples were collected from feedlots, holding pens, colon contents, hides, and carcasses. E. coli O157:H7 detection and confirmation was carried out using conventional microbiology techniques, immunomagnetic separation, latex agglutination, and the BAX system. A total of 97 E. coli O157 strains were recovered and screened for key virulence and metabolic genes using multiplex and conventional PCR. Eighty-eight (91.72%) of the strains carried stx2, eae, and ehxA genes. Ten isolates (8.25%) were atypical sorbitol-fermenting strains, and nine were negative for the flicH7 gene and lacked eae, stx1, stx2, and ehxA. One sorbitol-positive strain carried stx2, eae, tir, toxB, and iha genes but was negative for stx1 and ehxA. Pulsed-field gel electrophoresis (PFGE) analysis yielded 49 different PFGE subtypes, showing a high genetic diversity; however, the majority of the typical isolates were closely related (80 to 90% cutoff). Atypical O157 isolates were not closely related within them or to typical E. coli O157:H7 isolates. Identical PFGE subtypes were found in samples obtained from colon contents, feedlots, holding pens, and carcasses. Isolation of a sorbitolfermenting E. coli O157 positive for a number of virulence genes is a novel finding in Mexico. These data showed that genetically similar strains of E. coli O157:H7 can be found at various stages of beef production and highlights the importance of preventing cross-contamination at the pre- and postharvest stages of processing.

Highly selective trapping of enteropathogenic E. coli on Fabry-Pérot sensor mirrors

Untreated recycled water, such as sewage and graywater, will almost always contain a wide range of agents that are likely to present risks to human health, including chemicals and pathogenic microorganisms. The microbial hazards, such as large numbers of enteric pathogens that can cause gastroenteric illness if ingested, are the main cause of concern for human health. The presence of the enteropathogenic Escherichia coli (EPEC) serotype is of particular concern, as this group of bacteria is responsible for causing severe infant and travelers' diarrhea, gastroenteritis and hemolytic uremic syndrome. A biosensing system based on an optical Fabry-Pérot (FP) cavity, capable of directly detecting the presence of EPEC within 5 min, has been developed using a simple micro-thin double-sided adhesive tape and two semi-transparent FP mirror plates. The system utilizes a poly(methyl methacrylate) (PMMA) or glass substrates sputtered by 40-nm-thick gold thin films serving as FP mirrors. Mirrors have been activated using 0.1M mercaptopropionic acid, influencing an immobilization density of the translocated intimin receptor (TIR) of 100 ng/cm(2). The specificity of recognition was confirmed by exposing TIR functionalized surfaces to four taxonomically related and/or distantly related bacterial strains. It was found that the TIR-functionalized surfaces did not show any bacterial capture for these other bacterial strains within a 15 min incubation period.

In silico analysis of chimeric espA, eae and tir fragments of Escherichia coli O157:H7 for oral immunogenic applications

Background

In silico techniques are highly suited for both the discovery of new and development of existing vaccines. Enterohemorrhagic Escherichia coli O157:H7 (EHEC) exhibits a pattern of localized adherence to host cells, with the formation of microcolonies, and induces a specific histopathological lesion (attaching/effacing). The genes encoding the products responsible for this phenotype are clustered on a 35-kb pathogenicity island. Among these proteins, Intimin, Tir, and EspA, which are expressed by attaching-effacing genes, are responsible for the attachment to epithelial cell that leads to lesions.

Results

We designed synthetic genes encoding the carboxy-terminal fragment of Intimin, the middle region of Tir and the carboxy-terminal part of EspA. These multi genes were synthesized with codon optimization for a plant host and were fused together by the application of four repeats of five hydrophobic amino acids as linkers. The structure of the synthetic construct gene, its mRNA and deduced protein and their stabilities were analyzed by bioinformatic software. Furthermore, the immunogenicity of this multimeric recombinant protein consisting of three different domains was predicted.

Conclusion

a structural model for a chimeric gene from LEE antigenic determinants of EHEC is presented. It may define accessibility, solubility and immunogenecity.

Incidence and tracking of Escherichia coli O157:H7 in a major produce production region in California

Fresh vegetables have become associated with outbreaks caused by Escherichia coli O157:H7 (EcO157). Between 1995-2006, 22 produce outbreaks were documented in the United States, with nearly half traced to lettuce or spinach grown in California. Outbreaks between 2002 and 2006 induced investigations of possible sources of pre-harvest contamination on implicated farms in the Salinas and San Juan valleys of California, and a survey of the Salinas watershed. EcO157 was isolated at least once from 15 of 22 different watershed sites over a 19 month period. The incidence of EcO157 increased significantly when heavy rain caused an increased flow rate in the rivers. Approximately 1000 EcO157 isolates obtained from cultures of>100 individual samples were typed using Multi-Locus Variable-number-tandem-repeat Analysis (MLVA) to assist in identifying potential fate and transport of EcO157 in this region. A subset of these environmental isolates were typed by Pulse Field Gel Electrophoresis (PFGE) in order to make comparisons with human clinical isolates associated with outbreak and sporadic illness. Recurrence of identical and closely related EcO157 strains from specific locations in the Salinas and San Juan valleys suggests that transport of the pathogen is usually restricted. In a preliminary study, EcO157 was detected in water at multiple locations in a low-flow creek only within 135 meters of a point source. However, possible transport up to 32 km was detected during periods of higher water flow associated with flooding. During the 2006 baby spinach outbreak investigation, transport was also detected where water was unlikely to be involved. These results indicate that contamination of the environment is a dynamic process involving multiple sources and methods of transport. Intensive studies of the sources, incidence, fate and transport of EcO157 near produce production are required to determine the mechanisms of pre-harvest contamination and potential risks for human illness.

Structure of GrlR and the implication of its EDED motif in mediating the regulation of type III secretion system in EHEC

Enterohemorrhagic Escherichia coli (EHEC) is a common cause of severe hemorrhagic colitis. EHEC's virulence is dependent upon a type III secretion system (TTSS) encoded by 41 genes. These genes are organized in several operons clustered in the locus of enterocyte effacement. Most of the locus of enterocyte effacement genes, including grlA and grlR, are positively regulated by Ler, and Ler expression is positively and negatively modulated by GrlA and GrlR, respectively. However, the molecular basis for the GrlA and GrlR activity is still elusive. We have determined the crystal structure of GrlR at 1.9 A resolution. It consists of a typical beta-barrel fold with eight beta-strands containing an internal hydrophobic cavity and a plug-like loop on one side of the barrel. Strong hydrophobic interactions between the two beta-barrels maintain the dimeric architecture of GrlR. Furthermore, a unique surface-exposed EDED (Glu-Asp-Glu-Asp) motif is identified to be critical for GrlA-GrlR interaction and for the repressive activity of GrlR. This study contributes a novel molecular insight into the mechanism of GrlR function.

Bacterial gut infections

Infections of the bowel as a result of bacterial enteropathogens are one of the most common medical problems. The use of novel molecular biology techniques and the recent development of new antimicrobial drugs and vaccines are helping us to identify, understand, treat and prevent these infections.

Actin-dependent movement of bacterial pathogens

Listeria, Rickettsia, Burkholderia, Shigella and Mycobacterium species subvert cellular actin dynamics to facilitate their movement within the host cytosol and to infect neighbouring cells while evading host immune surveillance and promoting their intracellular survival. 'Attaching and effacing' Escherichia coli do not enter host cells but attach intimately to the cell surface, inducing motile actin-rich pedestals, the function of which is currently unclear. The molecular basis of actin-based motility of these bacterial pathogens reveals novel insights about bacterial pathogenesis and fundamental host-cell pathways.

STEC-EPEC oligonucleotide microarray: a new tool for typing genetic variants of the LEE pathogenicity island of human and animal Shiga toxin-producing Escherichia coli (STEC) and enteropathogenic E. coli (EPEC) strains

BACKGROUND

Shiga toxin-producing Escherichia coli (STEC) and enteropathogenic E. coli (EPEC) are important emerging pathogens that can cause a severe and sometimes fatal illness. Differentiation of eae, tir, espA, espD, and espB gene variants of the locus of enterocyte effacement (LEE) pathogenicity island represents an important tool for typing in routine diagnostics as well as in pathogenesis, epidemiologic, clonal, and immunologic studies.

METHODS

Type-specific oligonucleotide microarrays and a PCR scheme were designed and constructed for the detection and typing of genetic variants of the LEE genes. Oligonucleotide probes were tested for their specificity against the corresponding type strain by microarray hybridization using fluorescent DNA, either PCR-amplified (single, multiplex, long-range), chromosomal, or amplified chromosomal DNA.

RESULTS

The PCR scheme and the oligonucleotide microarray allowed us to distinguish 16 variants (alpha1, alpha2, beta1, beta2, gamma1, gamma2/theta, delta/kappa, epsilon, zeta, eta, iota, lambda, mu, nu, xi, omicron) of the eae gene, 4 variants (alpha1, beta1, gamma1, gamma2/theta) of the tir gene, 4 variants (alpha1, beta1, beta2, gamma1) of the espA gene, 3 variants (alpha1, beta1, gamma1) of the espB gene, and 3 variants (alpha1, beta1, gamma1) of the espD gene. We found a total of 12 different combinations of tir, espA, espB, and espD genes among the 25 typed strains.

CONCLUSIONS

The PCR scheme and the oligonucleotide microarray described are effective tools to rapidly screen multiple virulence genes and their variants in E. coli strains isolated from human and animal infections. The results demonstrate the great genetic diversity among LEE genes of human and animal STEC and EPEC strains.

Adhesins of Enterohemorrhagic Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC) was first recognized as a cause of human disease in 1983 and is associated with diarrhea and hemorrhagic colitis, which may be complicated by life-threatening renal and neurological sequelae. EHEC are defined by their ability to produce one or more Shiga-like toxins (Stx), which mediate the systemic complications of EHEC infections, and to induce characteristic attaching and effacing lesions on intestinal epithelia, a phenotype that depends on the locus of enterocyte effacement. Acquisition of Stx-encoding bacteriophages by enteropathogenic E. coli is believed to have contributed to the evolution of EHEC, and consequently some virulence factors are conserved in both pathotypes. A key requirement for E. coli to colonize the intestines and produce disease is the ability to adhere to epithelial cells lining the gastrointestinal tract. Here, we review knowledge of the adhesins produced by EHEC and other Stx-producing E. coli, with emphasis on genetic, structural, and mechanistic aspects and their contribution to pathogenesis.

A carboxy-terminal domain of Tir from enterohemorrhagic Escherichia coli O157:H7 (EHEC O157:H7) required for efficient type III secretion

The type III secreted protein Tir from Enterohemorrhagic Escherichia coli (EHEC O157:H7) plays a central role in adherence and pedestal formation during infection. Little is known about how Tir domains outside of the amino-terminus contribute to efficient Tir secretion and translocation. We found a 6 amino acid (519-524) carboxy-terminal region which was required for efficient Tir secretion and translocation. Interestingly, EHEC O157:H7 Tir(Delta)519-524 was efficiently secreted when expressed in the related pathogen enteropathogenic E. coli. These data suggest that this region may play a role in maintaining EHEC O157:H7 Tir in a secretion-competent conformation.

tir- and stx-positive Escherichia coli in stream waters in a metropolitan area

Diarrheagenic Escherichia coli, which may include the enteropathogenic E. coli and the enterohemorrhagic E. coli, are a significant cause of diarrheal disease among infants and children in both developing and developed areas. Disease outbreaks related to freshwater exposure have been documented, but the presence of these organisms in the urban aquatic environment is not well characterized. From April 2002 through April 2004 we conducted weekly surveys of streams in the metropolitan Baltimore, Md., area for the prevalence of potentially pathogenic E. coli by using PCR assays targeting the tir and stx(1) and stx(2) genes. Coliforms testing positive for the presence of the tir gene were cultured from 653 of 1,218 samples (53%), with a greater prevalence associated with urban, polluted streams than in suburban and forested watershed streams. Polluted urban streams were also more likely to test positive for the presence of one of the stx genes. Sequence analysis of the tir amplicon, as well as the entire tir gene from three isolates, indicated that the pathogenic E. coli present in the stream waters has a high degree of sequence homology with the E. coli O157:H7 serotype. Our data indicate that pathogenic E. coli are continually deposited into a variety of stream habitats and suggest that this organism may be a permanent member of the gastrointestinal microflora of humans and animals in the metropolitan Baltimore area.

Prevalence of the lpfO113 gene cluster among Escherichia coli O157 isolates from different sources

Domestic farm animals represent an important reservoir of infection for Shiga toxin-producing Escherichia coli (STEC). Nevertheless the bacterial factors required to colonise these hosts are poorly defined. In this study, the prevalence of a recently described fimbrial gene cluster, lpfO113, among human and animal isolates of STEC was investigated. lpfO113 has been shown to play a role in the adherence of STEC O113:H21 to epithelial cells. Here the presence of the lpfAO113 gene (predicted to encode a major fimbrial subunit) was examined by PCR in E. coli of serogroups O157 and O26 isolated from pigs (n=38), cattle (n=10), and humans (n=9). In addition, we tested for several other genetic virulence markers including Shiga toxin (stx), intimin (eae), the translocated intimin receptor (tir), EHEC-hemolysin (ehx) and F18 fimbriae (fedA). Overall 45 of the 57 strains (79%) possessed the lpfAO113 gene as determined by the presence of a 573 bp PCR product. Moreover, there was a close correlation between the presence of the lpfAO113 marker and the absence of the eae gene. lpfAO113 was found in all of pig isolates, suggesting a possible role in colonisation of the porcine host. In addition, several E. coli strains isolated from pigs had two fimbrial gene markers, fedA and lpfAO113. lpfAO113 was not present in strains of E. coli O157:H7 as described previously. Overall these results show that lpfAO113 is widely distributed among eae-negative E. coli isolates and thus may represent an important adherence factor in this group of pathogens.

HEp-2 cell adherence, actin aggregation, and intimin types of attaching and effacing Escherichia coli strains isolated from healthy infants in Germany and Australia

Fecal samples from healthy children under 2 years of age living in Berlin, Germany (205 infants), and Melbourne, Australia (184 infants), were investigated for the presence of attaching and effacing (AE) Escherichia coli (AEEC) strains by screening for eae (intimin) genes. Twenty-seven AEEC strains were isolated from 14 children (7.6%) from Melbourne and from 12 children (5.9%) from Berlin. The 27 AEEC strains were classified as enterohemorrhagic E. coli (one strain, producing Shiga toxin 1), typical enteropathogenic E. coli (EPEC) (one strain carrying an EPEC adherence factor [EAF] plasmid), and atypical EPEC (25 strains negative for Shiga toxins and EAF plasmids). The AEEC were divided into 18 different serotypes, O-nontypeable and O-rough strains. Typing of their intimin genes revealed the presence of intimin alpha in 6 strains, intimin beta in 11 strains, intimin gamma in 7 strains, intimin zeta in 2 strains, and intimin eta in one strain. Analysis of HEp-2 cell adherence showed diffuse adherence or localized adherence-like patterns in 26 AEEC strains; local adherence was found only with the EAF-positive strain. Ten AEEC strains showed an AE property with the fluorescent actin staining (FAS) test. The introduction of an EAF plasmid (pMAR7) converted 11 FAS-negative AEEC strains to FAS positive and increased the FAS reaction in six FAS-positive AEEC strains, indicating that the genes needed for the AE phenotype were functional in these strains. Our finding indicates that atypical EPEC strains could play a double role as strains that naturally immunize against intimin in humans and as reservoirs for new emerging human pathogenic EPEC strains.

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.

Effect of environmental conditions on proteins secreted by enterohemorrhagic Escherichia coli O26:H11

Infections due to Shiga toxin-producing Escherichia coli (STEC) are responsible for severe diarrheal diseases in humans, and these bacteria have recently emerged as a leading cause of renal failure and encephalitis in children and the aged. In this study, we examined the environment-dependent production of proteins secreted from a strain of STEC O26:H11 by trichloroacetic acid precipitation, SDS-PAGE, Western blotting and N-terminal amino acid sequence analysis. Growth of bacteria in essential minimum medium (M9) led to the detection of secreted proteins of 104, 80,40, 37 and 25 kDa (P104, P80, P40, P37 and P25, respectively). When grown in serum-free MEM, only P104, P40, P37 and P25 were observed in supernatant fluids. Growth of the bacteria in Luria-Bertani broth (LB) enhanced the expression of P104, but the productions of the other proteins were remarkably reduced. CO2 increased the secretion of P80 and P37, but reduced the production of P104. N-terminal amino acid sequencing revealed that P104 was EspP of STEC, which was homologous to EspC of enteropathogenic Escherichia coli (EPEC), and both proteins belong to a subclass of the IgA protease family. P80, which was identified as EspE of STEC, was homologous to Tir of EPEC. P40, P37 and P25 were found to be highly homologous to the similarly sized EspD, EspB and EspA proteins, previously detected in culture supernatants of EPEC. Those proteins are thought to be STEC virulence factors. Sera were obtained from two patients, one with colitis and another with hemolytic uremic syndrome (HUS), caused by STEC O157:H7, to study immune response to secreted proteins. Our results suggested that Tir caused immune response following STEC disease.

Human milk secretory antibodies against attaching and effacing Escherichia coli antigens

Secretory immunoglobulin A (sIgA) is a primary factor responsible for preventing attachment of enteropathogens to gut epithelium in breastfeeding infants. We compared the frequency of sIgA to major surface antigens of enterohemorrhagic Escherichia coli (EHEC) in milk of 123 women from the United States and Mexico to determine whether regional differences existed in the frequency of antibodies to these surface antigens. In both groups of women, milk commonly has sIgA against various EHEC lipopolysaccharides, EspA, EspB, intimin, and less frequently against Shiga toxin. The study suggests that persons living in the United States are exposed to attaching/effacing enteropathogens more frequently than is generally assumed. The low frequency of antibodies to Stx1 (in 12% of Mexican and in 22% of U.S. samples) suggests that the rare appearance of hemolytic uremic syndrome in adults is not due to neutralization of toxin at the gut level. Only anti-EspA is found in most milk samples from both populations of women. EspA may represent a useful target for an immunization strategy to prevent EHEC disease in humans.

Mucosal immunoadjuvant activity of the low toxic recombinant Escherichia coli heat-labile enterotoxin produced by Bacillus brevis for the bacterial subunit or component vaccine in pigs and cattle

A gene encoding the mature Escherichia coli heat-labile enterotoxin (LT) lacking the nick site in the A subunit by deleting tripeptides was introduced in a vector pNH301 and expressed extracellularly as mutant molecule of holotoxin at high levels in Bacilus brevis HPD31-S5 of the host bacterium. The mucosal adjuvant activities of the produced mutant LT (mLT) preparation were studied in pigs and cattle. Intranasal immunization of pigs with the recombinant subunit vaccine of Erysipelothrix rhusiopathiae or the component vaccine of Bordetella bronchiseptica mixed with the mLT resulted in a substantial enhancement of both mucosal and serum-specific antibody levels. The immunized pigs were also protected when challenge-exposed intradermally with a highly virulent E. rhusiopathiae strain or challenge-exposed intranasally with a highly virulent strain of B. bronchiseptica. The mLT intranasally administered with recombinant intimin (an outer membrane adhesin) of E. coli O157:H7 also induced an elevation of IgA-specific antibody in the nasal secretion and saliva of calves as well as an elevation of IgG1-specific antibody level against the intimin in the sera and colostrum of cows. The three kinds tested protein antigens were poorly immunogenic when antigen administered intranasally alone. The mLT intranasally administered at a higher effective dose did not induce local adverse reactions or diarrhea in pigs and cattle. The present study demonstrates that the recombinant mLT produced using the B. brevis expression system might represent promising immunoadjuvants for the potential application of intranasal vaccines directed against infectious diseases in pigs and cattle.

Detection and quantitation of enterohemorrhagic Escherichia coli O157, O111, and O26 in beef and bovine feces by real-time polymerase chain reaction

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 and certain non-O157 EHEC serotypes (such as O26:H11, O26: NM, O11:H8, and O111:NM) have emerged as significant causes of human disease throughout the world. Important virulence attributes of EHEC are the intimin protein (encoded by the eae gene) and Shiga toxins 1 and 2 (encoded by the stx1 and stx2 genes, respectively). Two sets of real-time polymerase chain reaction (R-PCR) assays were developed for the simultaneous detection and quantitation of EHEC through the monitoring of the presence of the eae and stx genes, and these assays were evaluated. In the eaeR-PCR assay, three sets of primers and TaqMan probes were designed for the amplification and real-time detection of a portion of the eae gene specific to the EHEC O26, O111, and O157 serotypes. In the stxR-PCR assay, two sets of primers and TaqMan probes were used to amplify and detect the stx1 and stx2 genes. DNA prepared from 67 bacterial strains carrying known virulence markers was tested to determine the specificities of the two assays. In the eaeR-PCR assay, eaeO157- and eaeO111-specific primer-probe sets identified only EHEC O157 and O111 strains, respectively. The eaeO26-specific primer-probe set identified all EHEC 026 isolates and some Shiga toxin-negative serotypes of enteropathogenic E. coli and rabbit diarrheagenic E. coli. The stxR-PCR assay was able to identify only those strains carrying either or both of the Shiga toxin-encoding genes. The detection range of both R-PCR assays was linear over DNA concentrations corresponding to 10(3) to 10(8) CFU/ml of an EHEC strain. Both assays were able to detect and quantify very low levels (1 to 10 CFU/g of food or feces) of EHEC in feces and ground beef enriched for 16 h in a modified Trypticase soy broth. In conclusion, eae- and stx-based R-PCR assays are reliable and sensitive methods for the rapid screening and specific and quantitative detection of important serotypes of EHEC in cattle and in foods of bovine origin.

Reactivity of convalescent-phase hemolytic-uremic syndrome patient sera with the megaplasmid-encoded TagA protein of Shiga toxigenic Escherichia coli O157

A cosmid library of Shiga toxigenic Escherichia coli (STEC) O157:H7 strain EDL933 DNA was screened for clones capable of reacting with convalescent-phase serum from a patient with hemolytic-uremic syndrome (HUS), in an attempt to identify candidate virulence genes. One of the immunoreactive clones contained a portion of the large plasmid pO157, and the immunoreactive gene product was identified as TagA. The function of this 898-amino-acid protein is unknown, but it exhibits 42% amino acid sequence identity and 63% similarity to a 312-amino-acid region of a ToxR-regulated lipoprotein of Vibrio cholerae. Antibodies to E. coli O157 TagA were detected in sera from other HUS patients with O157 STEC infection but not in those from patients whose illnesses were caused by other STEC types or in healthy controls. These data demonstrate that TagA is expressed in vivo and provide circumstantial evidence for a role in the pathogenesis of the disease. The tagA gene is present only in STEC strains belonging to serogroup O157, and so antibodies to TagA are a potentially useful serological marker for infections due to such strains.

Mechanism of action of EPEC type III effector molecules

Enteropathogenic E. coli (EPEC) is a prototypic member of the family of related 'attaching and effacing (A/E)' pathogens that induce diarrhoeal disease, especially to the young that can be fatal, of a wide range of mammalian species. Disease is correlated with the loss of absorptive gut epithelial microvilli and the reorganisation of host cytoskeletal proteins into pedestal-like structures beneath the adherent bacteria. These phenotypes are dependent on a pathogenicity island (LEE; Locus of Enterocyte Effacement) encoding a type III secretion system, secreted proteins, chaperone molecules, regulatory proteins and the bacterial outer membrane protein intimin. The type III secretion apparatus directs the transfer of specific proteins across the bacterial envelope, with a subset (EPEC secreted proteins - EspA, EspB and EspD) functioning to transfer effector proteins into host cells. These effector molecules subvert cellular processes that undoubtedly benefit the pathogen and contribute to disease. Three LEE-encoded EPEC effector molecules have so far been identified with one, Tir (Translocated intimin receptor), being transferred into host cells where it is modified by host kinases and becomes inserted into the plasma membrane to orchestrate cytoskeletal rearrangements linked to disease. This activity is dependent on its interaction with intimin and on tyrosine phosphorylation, with Tir-intimin interaction essential for virulence. A second effector Map, Mitochondrial-associated protein, is targeted to mitochondria where it has membrane-potential disrupting activity. The third, EspF disrupts intestinal barrier function and can induce host cell death by unknown mechanisms. Recent data relating to the mechanism by which Tir and Map function within host cells is discussed.

Immunological characterization of Escherichia coli O157:H7 intimin gamma1

Portions of the intimin genes of Escherichia coli O157:H7 strain E319 and of the enteropathogenic E. coli O127:H6 strain E2348/69 were amplified by PCR and cloned into pET-28a+ expression vectors. The entire 934 amino acids (aa) of E. coli O157:H7 intimin, the C-terminal 306 aa of E. coli O157:H7 intimin, and the C-terminal 311 aa of E. coli O127:H6 intimin were expressed as proteins fused with a six-histidine residue tag (six-His tag) in pET-28a+. Rabbit antisera raised against the six-His tag-full-length E. coli O157:H7 intimin protein fusion cross-reacted in slot and Western blots with outer membrane protein preparations from the majority of enterohemorrhagic and enteropathogenic E. coli serotypes which have the intimin gene. The E. coli strains tested included isolates from humans and animals which produce intimin types alpha (O serogroups 86, 127, and 142), beta1 (O serogroups 5, 26, 46, 69, 111, 126, and 128), gamma 1 (O serogroups 55, 145, and 157), gamma 2 (O serogroups 111 and 103), and epsilon (O serogroup 103) and a nontypeable intimin (O serogroup 80), results based on intimin type-specific PCR assays. Rabbit antisera raised against the E. coli O157:H7 C-terminal fusion protein were much more intimin type-specific than those raised against the full-length intimin fusion protein, but some cross-reaction with other intimin types was also observed for these antisera. In contrast, the monoclonal antibody Intgamma1.C11, raised against the C-terminal E. coli O157 intimin, reacted only with preparations from intimin gamma 1-producing E. coli strains such as E. coli O157:H7.

The elements of the locus of enterocyte effacement in human and wild mammal isolates of Escherichia coli: evolution by assemblage or disruption?

Escherichia coli is an excellent model for studying the evolution of pathogenicity since within one species various genes can be found in pathogenic islands and plasmids causing a wide spectrum of virulence. A collection of 122 strains from different human and wild mammal hosts were analysed by PCR and Southern hybridization for the presence of a subset of the genes included in the LEE (locus of enterocyte effacement). In the PCR analysis, two markers (cesT/eae and espB genes) were found together in more strains (25.4%) than either were found alone. The cesT/eae gene was less frequently found alone (8.2%) than was the espB gene (15.6%). Four regions of the LEE were analysed in a subsample of 25 strains using Southern hybridization. The four regions were all present (44%), all absent (12%) or present in different combinations (44%) in a given strain. The flanking regions of the LEE showed the highest rate of hybridization (in 72% of the strains). The results indicate that the LEE is a dynamic genetic entity, both the complete gene cluster and the individual genes. The genes that comprise this locus seem to be horizontally acquired (or lost) in an independent way and may control other functions in non-pathogenic E. coli lineages. In this way, horizontal transfer may allow the gradual stepwise construction of gene cassettes facilitating coordinate regulation and expression of novel functions.

Modulation of host cell signalling by enteropathogenic and Shiga toxin-producing Escherichia coli

The majority of Escherichia coli strains are harmless symbionts in the intestinal tract. However, there are several pathogenic forms, which are responsible for various diseases in humans and live stock. In this review we discuss the interactions between Shiga toxin-producing E. coli and enteropathogenic E. coli and their target host cells, describing their strategies to activate specific cellular signalling pathways which lead to subversion of critical physiological functions. We mainly concentrate on those pathogenic mechanisms that are dependent on a functional type III secretion system, but we also briefly discuss additional factors that contribute to the specific pathogenic profiles of Shiga toxin-producing E. coli and enreropathogenic E. coli.

The enterohaemorrhagic Escherichia coli (serotype O157:H7) Tir molecule is not functionally interchangeable for its enteropathogenic E. coli (serotype O127:H6) homologue

A major virulence determinant of enteropathogenic Escherichia coli (EPEC) is the Tir molecule that is translocated into the plasma membrane where it orchestrates cytoskeletal rearrangements. Tir undergoes several phosphorylation events within host cells, with modification on a tyrosine essential for its actin-nucleating function. The EHEC (serotype O157:H7) Tir homologue is not tyrosine phosphorylated implying that it uses an alternative mechanism to nucleate actin. This is supported in this study by the demonstration that EHEC Tir is unable to functionally substitute for its EPEC homologue. Like EPEC, the EHEC Tir molecule is phosphorylated within host cells, with the actin-nucleating dysfunction correlated to an altered modification profile. In contrast to EHEC Tir, the EPEC Tir molecule mediated actin nucleation whether delivered into host cells by either strain. Thus, it would appear that EHEC encodes specific factor(s) that facilitate the correct modification of its Tir molecule within host cells. Domain-swapping experiments revealed that the N-terminal, alpha-actinin binding, Tir domains were functionally interchangeable, with both the actin-nucleating dysfunction and altered modification profiles linked to the EHEC C-terminal Tir domain. This tyrosine-independent modification process presumably confers an advantage to EHEC O157:H7 and may contribute to the prevalence of this strain in EHEC disease. The presented data are also consistent with EPEC and EHEC sharing non-phosphotyrosine phosphorylation event(s), with an important role for such modifications in Tir function. An EHEC-induced phosphotyrosine dephosphorylation activity is also identified.

Studies about the mechanism of internalization by mammary epithelial cells of Escherichia coli isolated from persistent bovine mastitis

The purpose of this study was to investigate the interaction between Escherichia coli and primary mammary epithelial cell cultures derived from cows with persistent intramammary infection (IMI). Two strains of E. coli, isolated from the milk of two different cows suffering from persistent E. coli IMI were tested for adhesion to and invasion of three primary mammary epithelial cell cultures derived from mammary biopsies of the two infected cows. Intracellular E. coli were detected during five days post infection in vitro. Both strains of E. coli adhered to and invaded monolayers of all three primary mammary epithelial cell cultures. One strain adhered less but invaded more than the other. Comparison with other mammary pathogens indicated that E. coli invaded the cells less efficiently than Staphylococcus aureus, about as efficiently as Streptococcus dysgalactiae and more efficiently than Streptococcus uberis. The mechanism of E. coli invasion was studied using the cytoskeleton disrupting agents colchicine and cytochalasin D. These compounds inhibited the invasion of E. coli. Invasion of E. coli could also be inhibited by the phosphokinase inhibitors genistein and staurosporin in a dose-dependent fashion. Phorbol-myristyl-acetate (PMA) had no effect on the invasion of E. coli. Histology of mammary tissue revealed chronic inflammatory changes in quarters that were persistently infected by E. coli. Intracellular bacteria were not detected in mammary tissue sections. Polymerase chain reaction (PCR) analysis suggested that the two strains of E. coli lacked genes encoding for bundle-forming pili (bfpA), intimin (eae) and translocated intimin receptor (tir), which are characteristic for enteropathogenic E. coli (EPEC).

Complete nucleotide sequence and analysis of the locus of enterocyte Effacement from rabbit diarrheagenic Escherichia coli RDEC-1

The pathogenicity island termed the locus of enterocyte effacement (LEE) is found in diverse attaching and effacing pathogens associated with diarrhea in humans and other animal species. To explore the relation of variation in LEE sequences to host specificity and genetic lineage, we determined the nucleotide sequence of the LEE region from a rabbit diarrheagenic Escherichia coli strain RDEC-1 (O15:H-) and compared it with those from human enteropathogenic E. coli (EPEC, O127:H6) and enterohemorrhagic E. coli (EHEC, O157:H7) strains. Differing from EPEC and EHEC LEEs, the RDEC-1 LEE is not inserted at selC and is flanked by an IS2 element and the lifA toxin gene. The RDEC-1 LEE contains a core region of 40 open reading frames, all of which are shared with the LEE of EPEC and EHEC. orf3 and the ERIC (enteric repetitive intergenic consensus) sequence present in the LEEs of EHEC and EPEC are absent from the RDEC-1 LEE. The predicted promoters of LEE1, LEE2, LEE3, tir, and LEE4 operons are highly conserved among the LEEs, although the upstream regions varied considerably for tir and the crucial LEE1 promoter, suggesting differences in regulation. Among the shared genes, high homology (>95% identity) between the RDEC-1 and the EPEC and EHEC LEEs at the predicted amino acid level was observed for the components of the type III secretion apparatus, the Ces chaperones, and the Ler regulator. In contrast, more divergence (66 to 88% identity) was observed in genes encoding proteins involved in host interaction, such as intimin (Eae) and the secreted proteins (Tir and Esps). A comparison of the highly variable genes from RDEC-1 with those from a number of attaching and effacing pathogens infecting different species and of different evolutionary lineages was performed. Although RDEC-1 diverges from some human-infecting EPEC and EHEC, most of the variation observed appeared to be due to evolutionary lineage rather than host specificity. Therefore, much of the observed hypervariability in genes involved in pathogenesis may not represent specific adaptation to different host species.

Up-regulation of both intimin and eae-independent adherence of shiga toxigenic Escherichia coli O157 by ler and phenotypic impact of a naturally occurring ler mutation

Shiga toxigenic Escherichia coli (STEC) strains are important human pathogens which are capable of causing diarrhea, hemorrhagic colitis, and the potentially fatal hemolytic-uremic syndrome (HUS). An important virulence trait of certain STEC strains, such as those belonging to serogroup O157, is the capacity to produce attaching and effacing (A/E) lesions on enterocytes, a property encoded by the locus for enterocyte effacement (LEE). LEE contains the eae gene, which encodes intimin, an outer membrane protein which mediates the intimate attachment of bacteria to the host epithelial cell surface, and eae is routinely used as a marker for LEE-positive STEC strains. However, the O157:H(-) STEC strain 95SF2 carries eae but did not produce A/E lesions on HEp-2 cells, as judged by a fluorescent actin staining assay. In this assay, 95SF2 adhered poorly to the HEp-2 cells, and those that did bind exhibited abnormal cell division. In contrast, the O157:H7 STEC strain EDL933 adhered strongly and produced typical A/E lesions. We have demonstrated that 95SF2 carries a defective LEE regulatory gene, ler, with a single base change with respect to that published for ler of EDL933, resulting in an Ile(57)-to-Thr substitution. Ler shows homology to H-NS-like regulators, which are modulators of transcription, and the mutation occurs in a domain implicated in oligomerization. 95SF2 was able to adhere and produce A/E lesions on HEp-2 cells when EDL933 ler was expressed from a multicopy plasmid. Conversely, introduction of a plasmid carrying 95SF2 ler into EDL933 abolished adherence and capacity to form A/E lesions. Studies with eae deletion derivatives of 95SF2 and EDL933 demonstrated that the ler-mediated adherence to HEp-2 cells is largely independent of intimin. We have also demonstrated that EDL933 ler, but not 95SF2 ler, increases the level of intimin in O157 STEC.

The locus for enterocyte effacement (LEE) of enteropathogenic Escherichia coli (EPEC) from dogs and cats

Enteropathogenic Escherichia coli (EPEC) produce attaching and effacing lesions. The genes responsible for this lesion are clustered on the chromosome forming a 35.5 kilobase pathogenesis island called LEE. The LEE was identified, characterized and completely sequenced from the human EPEC strain E2348/69. The LEE carries genes coding for: a type III secretion system (genes esc and sep), the translocated intimin receptor (gene tir), the outer membrane protein intimin (gene eae) and the E. coli secreted proteins EspA, EspB, and EspD (genes esp). In addition to man and farm animals, EPEC are also isolated from dogs and cats. We studied structurally and functionally the LEE of dog and cat EPEC. First, we used four probes scattered along the LEE to identify the presence of a LEE in canine and feline EPEC isolates. Second, by PCR, we checked the presence of genes homologous to eae, sep, esp, and tir genes in these strains. Third, since the four types of eae and tir genes were described, we developed a multiplex PCR in order to determine the type of eae and tir genes present in each strain. Fourth, we determined by PCR the site of the LEE insertion on the chromosome. Fifth, we tested several of the canine EPEC in their capacity to induce attaching and effacing lesions in the rabbit intestinal loop assay. We can conclude from this study: first, that the a LEE-like structure is present in all tested strains and that it contains genes homologous to esp, sep, tir, and eae genes; second, that there is some preferential associations between the type of eae gene and the type of tir gene present in a strain; third, that the majority of the tested strains contained a LEE located elsewhere on the chromosome in comparison to the human EPEC strain E2348/69; and fourth that dog EPEC were able to induce attaching and effacing lesions in rabbit ileal loop assay.

Shiga Toxin-Producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) are emerging as a significant source of foodborne infectious disease in the developed world. Multistate outbreaks of E. coli O157 and non-O157 serogroups in the United States are facilitated by the centralization of food processing and distribution. Our ability to recognize the clonality of these clusters has been advanced by developments in molecular detection techniques and in the establishment of active surveillance practices. These studies have helped identify important risk factors for both sporadic and outbreak STEC infection, allowing us to develop appropriate prevention strategies. Identification of these factors is of critical importance because of the lack of adequate treatments available. This brief review of the literature discusses major developments in the epidemiology, pathogenesis, diagnosis, treatment, and prevention of STEC disease published in the past few years.

Bacterial infections of the small intestine and colon

Bacterial infections of the small and large intestine are widespread and continue to be topics of active research. Surveys document the importance of diarrheal disease in many settings. Major breakthroughs in the understanding of pathogenic mechanisms (especially the interactions of bacteria and intestinal cells) continue, particularly with respect to shigella, salmonella, Yersinia species, and enteropathogenic Escherichia coli. Pathogenic mechanisms of other bacteria, such as campylobacter and entero-aggregative E. coli, are not well defined. Vaccines for cholera and typhoid fever are available, and new vaccines are in various stages of development ranging from synthesis of novel constructs to large-scale field trials. Several candidate vaccines are being exploited as carriers of antigens from other pathogens. Extraintestinal complications from salmonella, shigella, campylobacter, Yersinia species, and Shiga toxin-expressing E. coli are receiving much attention. Genomic sequencing of several of these pathogens is underway. The impact of this work is hard to predict, but expectations are high.

Human colostrum and serum contain antibodies reactive to the intimin-binding region of the enteropathogenic Escherichia coli translocated intimin receptor

BACKGROUND

In Brazil, enteropathogenic Escherichia coli (EPEC) diarrhoea is endemic in young infants. A characteristic feature of EPEC adhesion to host cells is intimate attachment leading to the formation of distinctive "attaching and effacing" (A/E) lesions on mammalian cells. Two genes directly involved in intimate adhesion, eae and tir, encode the adhesion molecule intimin and its translocated receptor Tir, respectively. The intimin-binding domain of Tir was recently mapped to the middle part of the polypeptide (Tir-M), and the amino (Tir-N) and carboxy (Tir-C) termini were found to be located within infected host cells. Recently, it was shown that colostrum samples from mothers living in Sao Paulo contain IgA-class antibodies reactive with a number of proteins associated with EPEC virulence. It has also been shown that patients infected with verocytotoxin-producing E. coli O157 can produce antibodies to Tir. In the current study antibody responses to the different Tir domains were analyzed in sera and colostrum samples collected in an EPEC-endemic area of Brazil.

METHODS

Recombinant Tir, Tir-N, Tir-M, and Tir-C were expressed as His-tagged protein in E. coli BL21a and purified on nickel columns. Western blot analysis was used to investigate colostrum IgA- and serum IgG-class antibodies reactive with the Tir fragments.

RESULTS

Anti-Tir IgG antibodies were detected in the serum of children, with (63%) or without (50%) diarrhoea. Anti-Tir IgA-class antibodies were detected in all the colostrum pools tested. With the use of both serum IgG- and colostrum IgA-class antibodies, an immunodominant domain of the Tir-polypeptide, Tir M, was identified.

CONCLUSION

The intimin-binding region of Tir (Tir-M) is the immunodominant region of the polypeptide in humans. Both serum IgG-class and colostrum IgA-class antibodies reacted predominantly with the Tir-M domain.

Shiga toxin-producing Escherichia coli can impair T84 cell structure and function without inducing attaching/effacing lesions

Enteropathogenic Escherichia coli (EPEC) intimately adhere to epithelial cells producing cytoskeletal rearrangement with typical attaching and effacing lesions and altered epithelial barrier and transport function. Since EPEC and Shiga toxin-producing E. coli (STEC) share similar genes in the "locus for enterocyte effacement" (LEE) thought to cause these changes, it has been assumed that STEC shares similar pathogenic mechanisms with EPEC. The aims of this study were to compare the effects of EPEC and STEC on bacterial-epithelial interactions and to examine changes in epithelial function. T84 monolayers were infected with STEC O157:H7 (wild strain EDL 933 or non-toxin-producing strain 85/170), EPEC (strain E2348/69), or HB101 (nonpathogenic) and studied at various times after infection. EPEC bound more avidly than EDL 933, but both strains exhibited greater binding than HB101. Attaching and effacing lesions and severe disruption to the actin cytoskeleton were observed in EPEC by 3 h postinfection but not in EDL 933 or HB101 at any time point. EPEC and EDL 933 increased monolayer permeability to [(3)H]mannitol 5- to 10-fold. In contrast to EPEC, EDL 933 completely abolished secretagogue-stimulated anion secretion as assessed under voltage clamp conditions in Ussing chambers. Several other STEC strains induced changes similar to those of EDL 933. In conclusion, STEC impairs epithelial barrier function and ion transport without causing major disruption to the actin cytoskeleton. Pathogenic factors other than products of LEE may be operant in STEC.

Molecular characterization of the locus encoding biosynthesis of the lipopolysaccharide O antigen of Escherichia coli serotype O113

Shiga toxigenic Escherichia coli (STEC) strains are a diverse group of organisms capable of causing severe gastrointestinal disease in humans. Within the STEC family, eae-positive STEC strains, particularly those belonging to serogroups O157 and O111, appear to have greater virulence for humans. However, in spite of being eae negative, STEC strains belonging to serogroup O113 have frequently been associated with cases of severe STEC disease, including hemolytic-uremic syndrome (HUS). Western blot analysis with convalescent-phase serum from a patient with HUS caused by an O113:H21 STEC strain indicated that human immune responses were directed principally against lipopolysaccharide O antigen. Accordingly, the serum was used to isolate a clone expressing O113 O antigen from a cosmid library of O113:H21 DNA constructed in E. coli K-12. Sequence analysis indicated that the O113 O-antigen biosynthesis (rfb) locus contains a cluster of nine genes which may be cotranscribed. Comparison with sequence databases identified candidate genes for four glycosyl transferases, an O-acetyl transferase, an O-unit flippase, and an O-antigen polymerase, as well as copies of galE and gnd. Two additional, separately transcribed genes downstream of the O113 rfb region were predicted to encode enzymes involved in synthesis of activated sugar precursors, one of which (designated wbnF) was essential for O113 O-antigen synthesis, and so is clearly a part of the O113 rfb locus. Interestingly, expression of O113 O antigen by E. coli K-12 significantly increased in vitro adherence to both HEp-2 and Henle 407 cells.

Comparison of eae, tir, espA and espB genes of bovine and human attaching and effacing Escherichia coli by multiplex polymerase chain reaction

Attaching and effacing Escherichia coli (AEEC) virulence genes include the eae, the tir, the espA and the espB genes. These genes have been sequenced from several AEEC strains. The sequences alignments revealed the presence of constant and variable regions. Multiplex polymerase chain reactions were developed, in order to determine the subtype of each gene present in a particular isolate. AEEC strains isolated from calves dead of diarrhea, from healthy calves and from infected humans were compared. The same pathotypes were found in sick and healthy calves but in inverted proportion. These pathotypes were also found in human AEEC. Although, the human EHEC strains from serotype O157 possessed their own pathotype.

Heterogeneity of the eae genes in attaching/effacing Escherichia coli from cattle: comparison with human strains

Enteropathogenic (EPEC) and enterohaemorrhagic (EHEC) Escherichia coli isolated from cattle were studied by DNA colony hybridization to subtype their intimin-encoding (eae) gene with probes derived from the variable parts of the eae alpha gene of the human EPEC strain E2348/69, the eae gamma gene of the human O157:H7 EHEC strain ATCC43888, and the eae beta gene of the bovine O26:H- EHEC strain 193, whose eae gene was first cloned and sequenced during this work. The EPEC and EHEC had been isolated from diarrhoeic calves (143 EPEC and 48 EHEC) and from healthy animals at the slaughterhouse (10 EPEC and 34 EHEC). The 191 bovine EPEC and EHEC isolated from diseased calves were positive with the Eae beta probe (55 and 27% respectively) and with the Eae gamma probe (9 and 73% respectively), whereas 52 EPEC (36%) were negative with the Eae alpha, Eae beta, and Eae gamma probes. The results were different for the 44 bovine EPEC and EHEC isolated from healthy cattle at slaughterhouses: most tested positive with the Eae gamma probe (80 and 82% respectively) and the remaining (20 and 18% respectively) with the Eae beta probe. Nine O26 human EHEC tested positive with the Eae beta probe and seven O111 with the Eae gamma probe. The bovine and human EPEC and EHEC belonging to these two serogroups gave identical results: the 18 bovine and human O26 isolates tested positive with the Eae beta probe, whereas the 13 O111 isolates were positive with the Eae gamma probe. In contrast, the isolates belonging to other serogroups (O5, O15, O18, O20, and O118) gave more variable results. The eae beta and eae gamma, but not the eae alpha, variants were thus distributed amongst bovine EPEC and EHEC. The eae beta variant seemed to be more frequently associated with the presence of clinical signs in calves, but one third of EPEC from diarrhoeic calves carried an eae gene variant other than the alpha, beta, or gamma variants. In addition, the use of these gene probes did not enable differentiation between bovine and human EHEC belonging to the same O serogroup.

Enterohemorrhagic Escherichia coli O157:H7 produces Tir, which is translocated to the host cell membrane but is not tyrosine phosphorylated

Intimate attachment to the host cell leading to the formation of attaching and effacing (A/E) lesions is an essential feature of enterohemorrhagic Escherichia coli (EHEC) O157:H7 pathogenesis. In a related pathogen, enteropathogenic E. coli (EPEC), this activity is dependent upon translocation of the intimin receptor, Tir, which becomes tyrosine phosphorylated within the host cell membrane. In contrast, the accumulation of tyrosine-phosphorylated proteins beneath adherent EHEC bacteria does not occur, leading to questions about whether EHEC uses a Tir-based mechanism for adherence and A/E lesion formation. In this report, we demonstrate that EHEC produces a functional Tir that is inserted into host cell membranes, where it serves as an intimin receptor. However, unlike in EPEC, in EHEC Tir is not tyrosine phosphorylated yet plays a key role in both bacterial adherence to epithelial cells and pedestal formation. EHEC, but not EPEC, was unable to synthesize Tir in Luria-Bertani medium but was able to secrete Tir into M9 medium, suggesting that Tir synthesis and secretion may be regulated differently in these two pathogens. EHEC Tir and EPEC Tir both bind intimin and focus cytoskeletal rearrangements, indicating that tyrosine phosphorylation is not needed for pedestal formation. EHEC and EPEC intimins are functionally interchangeable, but EHEC Tir shows a much greater affinity for EHEC intimin than for EPEC intimin. These findings highlight some of the differences and similarities between EHEC and EPEC virulence mechanisms, which can be exploited to further define the molecular basis of pedestal formation.