Detection of EspB using reversed passive latex agglutination: application to determination of enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli—A Summary of the Literature

Diarrheal disease is still a major public health concern, as it is still considered an important cause of death in children under five years of age. A few decades ago, the detection of enteropathogenic E. coli was made by detecting the O, H, and K antigens, mostly by agglutination. The recent protocols recommend the molecular methods for diagnosing EPEC, as they can distinguish between typical and atypical EPEC by identifying the presence/absence of specific virulence factors. EPEC are defined as diarrheagenic strains of E. coli that can produce attaching and effacing lesions on the intestinal epithelium while being incapable of producing Shiga toxins and heat-labile or heat-stable enterotoxins. The ability of these strains to produce attaching and effacing lesions enable them to cause localized lesions by attaching tightly to the surface of the intestinal epithelial cells, disrupting the surfaces of the cells, thus leading to the effacement of the microvilli. EPEC are classified on typical and atypical isolates, based on the presence or absence of E. coli adherence factor plasmids. All the EPEC strains are eae positive; typical EPEC strains are eae+, bfpA+, while atypical strains are eae+, bfpA−. No vaccines are currently available to prevent EPEC infections.

Effects of Psidium guajava leaf extract on secretion systems of Gram-negative enteropathogenic bacteria

We screened a total of 672 plant-tissue extracts to search for phytochemicals that inhibit the function of the type III secretion system (T3SS) of enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC). Among candidates examined, we found that an extract from the leaves of Psidium guajava (guava) inhibited the secretion of the EspB protein from EPEC and EHEC without affecting bacterial growth. The guava extract (GE) also inhibited EPEC and EHEC from adhering to and injecting EspB protein into HEp-2 cells. GE seemed to block the translocation of EspB from the bacterial cells to the culture medium. In addition to EPEC and EHEC, GE also inhibited the T3SS of Yersinia pseudotuberculosis and Salmonella enterica serovar Typhimurium. After exposure to GE, Y. pseudotuberculosis stopped the secretion of Yop proteins and lost its ability to induce the apoptosis of mouse bone marrow-derived macrophages. S. Typhimurium exposed to GE ceased the secretion of Sip proteins and lost its ability to invade HEp-2 cells. GE inhibited EspC secretion, the type V secretion protein of EPEC, but not Shiga toxin2 from EHEC. Thus, our results suggest that guava leaves contain a novel type of antimicrobial compound that could be used for the therapeutic treatment and prevention of gram-negative enteropathogenic bacterial infections.

Immunogenic Domains and Secondary Structure of Escherichia coli Recombinant Secreted Protein Escherichia coli-Secreted Protein B

Several pathogenic bacteria are able to induce the attaching and effacing (A/E) lesion. The A/E lesion is caused by effector proteins, such as Escherichia coli-secreted protein B (EspB), responsible together with Escherichia coli-secreted protein D for forming a pore structure on the host cell, which allows the translocation of effector proteins. Different variants of this protein can be found in E. coli strains, and during natural infection or when this protein is injected, this leads to variant-specific production of antibodies, which may not be able to recognize other variants of this bacterial protein. Herein, we describe the production of a hybrid recombinant EspB toxin that comprises all known variants of this protein. This recombinant protein could be useful as an antigen for the production of antibodies with broad-range detection of EspB-bearing bacteria, or as an antigen that could be used in vaccine formulation to generate antibodies against different EspB variants, thereby increasing immunization potential. In addition, the recombinant protein allowed us to analyze its secondary structure, to propose the immunogenic regions of EspB variants, and also to characterize anti-EspB antibodies. Our results suggest that this hybrid protein or a protein composed of the conserved immunogenic regions could be used for a variety of clinical applications.

Diarrheagenic Escherichia coli

Most Escherichia coli strains live harmlessly in the intestines and rarely cause disease in healthy individuals. Nonetheless, a number of pathogenic strains can cause diarrhea or extraintestinal diseases both in healthy and immunocompromised individuals. Diarrheal illnesses are a severe public health problem and a major cause of morbidity and mortality in infants and young children, especially in developing countries. E. coli strains that cause diarrhea have evolved by acquiring, through horizontal gene transfer, a particular set of characteristics that have successfully persisted in the host. According to the group of virulence determinants acquired, specific combinations were formed determining the currently known E. coli pathotypes, which are collectively known as diarrheagenic E. coli. In this review, we have gathered information on current definitions, serotypes, lineages, virulence mechanisms, epidemiology, and diagnosis of the major diarrheagenic E. coli pathotypes.

Monoclonal antibodies against all known variants of EspA: development of a simple diagnostic test for enteropathogenic Escherichia coli based on a key virulence factor

Enteropathogenic Escherichia coli (EPEC) are a major cause of infant diarrhoea in developing countries and a significant public health issue in industrialized countries. Currently there are no simple tests available for the diagnosis of EPEC. Serology of O-antigens is widely used routinely in many laboratories throughout the world, even though it has been known for many years to be an unreliable indicator of EPEC virulence. We have developed a simple, low-cost immunodiagnostic test based on the EspA filament, an essential virulence factor of EPEC and the related enterohaemorrhagic E. coli (EHEC). Using recombinant proteins of the five major variants of EspA as immunogens, we raised a panel of three monoclonal antibodies in mice that detects all variants of the native target in bacterial cultures. The antibodies proved suitable for application in sandwich-type assays, including ELISA and lateral flow immunoassays (LFI). Prototypes for both assays were specific for EPEC and EHEC strains when tested against a panel of control micro-organisms. We have also developed a simple, affordable culture medium, A/E medium, which optimizes expression of EspA allowing improved sensitivity of detection compared with standard Dulbecco's modified Eagle's medium. Together these reagents form the basis of robust, informative tests for EPEC for use especially in developing countries but also for routine screening in any clinical laboratory.

Development of a rapid agglutination latex test for diagnosis of enteropathogenic and enterohemorrhagic Escherichia coli infection in developing world: defining the biomarker, antibody and method

Background

Enteropathogenic and enterohemorrhagic Escherichia coli (EPEC/EHEC) are human intestinal pathogens responsible for diarrhea in both developing and industrialized countries. In research laboratories, EPEC and EHEC are defined on the basis of their pathogenic features; nevertheless, their identification in routine laboratories is expensive and laborious. Therefore, the aim of the present work was to develop a rapid and simple assay for EPEC/EHEC detection. Accordingly, the EPEC/EHEC-secreted proteins EspA and EspB were chosen as target antigens.

Methodology

First, we investigated the ideal conditions for EspA/EspB production/secretion by ELISA in a collection of EPEC/EHEC strains after cultivating bacterial isolates in Dulbecco’s modified Eagle’s medium (DMEM) or DMEM containing 1% tryptone or HEp-2 cells-preconditioned DMEM, employing either anti-EspA/anti-EspB polyclonal or monoclonal antibodies developed and characterized herein. Subsequently, a rapid agglutination latex test (RALT) was developed and tested with the same collection of bacterial isolates.

Principal findings

EspB was defined as a biomarker and its corresponding monoclonal antibody as the tool for EPEC/EHEC diagnosis; the production of EspB was better in DMEM medium. RALT assay has the sensitivity and specificity required for high-impact diagnosis of neglected diseases in the developing world.

Conclusion

RALT assay described herein can be considered an alternative assay for diarrhea diagnosis in low-income countries since it achieved 97% sensitivity, 98% specificity and 97% efficiency.

A rapid and low-cost diagnosis for EPEC/EHEC infections is extremely required considering their global prevalence, the severity of the diseases associated with them, and the fact that the use of antibiotics to treat EHEC infections can be harmful. For EHEC, the detection of Stx toxins has already been developed, but for EPEC, an internationally recognized standard diagnostic test is lacking. Thus, the approach for their rapid detection in this study was the use of the secreted proteins EspA and/or EspB, since they are the major secreted proteins in both pathogens. EspB was defined as a biomarker and its corresponding monoclonal antibody as the tool for EPEC/EHEC diagnosis using a latex agglutination assay, which can be employed in less equipped laboratories in developing countries.

Development and application of lateral flow test strip technology for detection of infectious agents and chemical contaminants: a review

Recent progress in the laboratory has been a result of improvements in rapid analytical techniques. An update of the applications of lateral flow tests (also called immunochromatographic assay or test strip) is presented in this review manuscript. We emphasized the description of this technology in the detection of a variety of biological agents and chemical contaminants (e.g. veterinary drugs, toxins and pesticides). It includes outstanding data, such as sample treatment, sensitivity, specificity, accuracy and reproducibility. Lateral flow tests provide advantages in simplicity and rapidity when compared to the conventional detection methods.

Bovine colostrum contains immunoglobulin G antibodies against intimin, EspA, and EspB and inhibits hemolytic activity mediated by the type three secretion system of attaching and effacing Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC) is the main cause of hemolytic-uremic syndrome, an endemic disease in Argentina which had an incidence in 2005 of 13.9 cases per 100,000 children younger than 5 years old. Cattle appear to be a major reservoir of EHEC, and a serological response to EHEC antigens has been demonstrated in natural and experimental infections. In the current study, antibodies against proteins implicated in EHEC's ability to form attaching and effacing lesions, some of which are exported to the host cell via a type three secretion system (TTSS), were identified in bovine colostrum by Western blot analysis. Twenty-seven (77.0%) of the 35 samples examined contained immunoglobulin G (IgG) antibodies against the three proteins assayed in this study: EspA, EspB, and the carboxy-terminal 280 amino acids of gamma-intimin, an intimin subtype associated mainly with O157:H7 and O145:H- serotypes. Every colostrum sample was able to inhibit, in a range between 45.9 and 96.7%, the TTSS-mediated hemolytic activity of attaching and effacing E. coli. The inhibitory effect was partially mediated by IgG and lactoferrin. In conclusion, we found that early colostrum from cows contains antibodies, lactoferrin, and other unidentified substances that impair TTSS function in attaching and effacing E. coli strains. Bovine colostrum might act by reducing EHEC colonization in newborn calves and could be used as a prophylactic measure to protect non-breast-fed children against EHEC infection in an area of endemicity.

Development of a rapid immunochromatographic test to identify enteropathogenic and enterohemorrhagic Escherichia coli by detecting EspB

A rapid immunochromatographic (IC) test to identify enteropathogenic and enterohemorrhagic Escherichia coli (EPEC and EHEC, respectively) was developed to detect EspB secreted by the type III secretion system of these bacteria. The detection limit of the test system was 4 ng/mL. All 33 of 34 strains harboring the eae gene encoding intimin were positive in the IC test, and all 40 of the eae-negative strains were negative. The results showed that the sensitivity was 96.9% and specificity was 100%. The IC test also detected EspB in a stool sample artificially supplemented with 60 ng EspB/mL. The IC test for the detection of EspB may be a practical method to define EPEC or EHEC both in clinical laboratories and the field.

Detection of PCR amplicons from bacterial pathogens using microsphere agglutination

For rapid and inexpensive detection of polymerase chain reaction (PCR) amplicons, a novel microsphere agglutination assay has been developed. PCR is carried out using biotinylated forward and reverse primers, and the amplified DNA fragments are able to agglutinate streptavidin-coated microspheres (5.7 microm in diameter). Purification of PCR amplicons is unnecessary when initial primer concentrations are 250 nM. Agglutination can be identified visually within 2 min without any additional equipment or reagents. Using listeriolysin (lisA)-specific biotinylated primers, we have successfully detected and identified Listeria monocytogenes lisA+ cells among Salmonella typhimurium, Staphylococcus aureus, Campylobacter jejuni and Escherichia coli O157:H7 cells. The simplicity of this protocol considerably reduces the time and cost of diagnostic PCR experiments. This procedure is potentially useful for various studies and field applications.

Multiplex PCR assay for identification of human diarrheagenic Escherichia coli

A multiplex PCR assay for the identification of human diarrheagenic Escherichia coli was developed. The targets selected for each category were eae for enteropathogenic E. coli, stx for Shiga toxin-producing E. coli, elt and est for enterotoxigenic E. coli, ipaH for enteroinvasive E. coli, and aggR for enteroaggregative E. coli. This assay allowed the categorization of a diarrheagenic E. coli strain in a single reaction tube.