Synthesis of PDA-Mediated Magnetic Bimetallic Nanozyme and Its Application in Immunochromatographic Assay

Immunochromatographic assay (ICA) is widely applied in various fields. However, severe matrix interference and weak signal output present major challenges in achieving accurate and ultrasensitive detection in ICA. Here, a polydopamine (PDA)-mediated magnetic bimetallic nanozyme (Fe₃O₄@PDA@Pd/Pt) with peroxidase-like activity was synthesized and used as a probe in ICA. The magnetic property of Fe₃O₄@PDA@Pd/Pt enabled effective magnetic enrichment of targets, thereby reducing the matrix interference in the sample. PDA coating on the magnetic bimetallic nanozyme was employed as a mediator and a stabilizer. It improved the catalytic ability and stability of the magnetic bimetallic nanozyme by providing more coordination sites for Pd/Pt growth and functional groups (-NH and -OH). In addition, the Pd/Pt bimetallic synergistic effect could further enhance the catalytic ability of the nanozyme. A method was developed by integrating Fe₃O₄, PDA, and Pd/Pt into Fe₃O₄@PDA@Pd/Pt as a probe in ICA. With the proposed method, human chorionic gonadotropin and Escherichia coli O157:H7 were successfully detected to be as low as 0.0094 mIU/mL in human blood serum and 9 × 10¹ CFU/mL in the milk sample, respectively. This method may be readily adapted for accurate and ultrasensitive detection of other biomolecules in various fields.

Identification of Nanobodies Blocking Intimate Adherence of Shiga Toxin-Producing Escherichia coli to Epithelial Cells

Therapeutic antibodies (Abs) inhibiting bacterial adhesion to host epithelia are an attractive option to reduce the load of Shiga toxin-producing E. coli (STEC) in the intestine of the patient and also in the bovine reservoir, thereby minimizing the risk of STEC contamination in the food chain. Of particular interest are recombinant single-domain Ab fragments called nanobodies (Nbs) derived from the variable domain of camelid heavy chain-only antibodies (VHH). The outer membrane adhesin intimin and the translocated intimin receptor (Tir) are essential for the attachment of STEC to host epithelia. In addition, EspA filaments of the bacterial type III protein secretion system are needed for Tir translocation into the host cell. Given their importance for bacterial adhesion and colonization, we developed Nbs against intimin, Tir and EspA proteins of STEC serotype O157:H7. Here, we report the screening methods used to isolate inhibitory Nbs blocking intimin-Tir protein-protein interaction, actin-pedestal formation, and intimate adhesion of STEC to epithelial cells in vitro. First, we describe how VHH gene repertoires can be produced as Nbs secreted by E. coli using the α-hemolysin (HlyA) protein secretion system. Next, we report the methods for identification of inhibitors of intimin-Tir protein-protein interaction and of STEC intimate adhesion to HeLa cells in culture. These methods can be adapted for the screening of Nbs against different adhesin-receptor complexes to block the adhesion of other pathogens to host cells.

Cattle intestinal microbiota shifts following Escherichia coli O157:H7 vaccination and colonization

Vaccination-induced Escherichia coli O157:H7-specific immune responses have been shown to reduce E. coli O157:H7 shedding in cattle. Although E. coli O157:H7 colonization is correlated with perturbations in intestinal microbial diversity, it is not yet known whether vaccination against E. coli O157:H7 could cause shifts in bovine intestinal microbiota. To understand the impact of E. coli O157:H7 vaccination and colonization on intestinal microbial diversity, cattle were vaccinated with two doses of different E. coli O157:H7 vaccine formulations. Six weeks post-vaccination, the two vaccinated groups (Vx-Ch) and one non-vaccinated group (NonVx-Ch) were orally challenged with E. coli O157:H7. Another group was neither vaccinated nor challenged (NonVx-NonCh). Fecal microbiota analysis over a 30-day period indicated a significant (FDR corrected, p <0.05) association of bacterial community structure with vaccination until E. coli O157:H7 challenge. Shannon diversity index and species richness were significantly lower in vaccinated compared to non-vaccinated groups after E. coli O157:H7 challenge (p < 0.05). The Firmicutes:Bacteroidetes ratio (p > 0.05) was not associated with vaccination but the relative abundance of Proteobacteria was significantly lower (p < 0.05) in vaccinated calves after E. coli O157:H7 challenge. Similarly, Vx-Ch calves had higher relative abundance of Paeniclostridium spp. and Christenellaceae R7 group while Campylobacter spp., and Sutterella spp. were more abundant in NonVx-Ch group post-E. coli O157:H7 challenge. Only Vx-Ch calves had significantly higher (p < 0.001) E. coli O157:H7-specific serum IgG but no detectable E. coli O157:H7-specific IgA. However, E. coli O157:H7-specific IL-10-producing T cells were detected in vaccinated animals prior to challenge, but IFN-γ-producing T cells were not detected. Neither E. coli O157:H7-specific IgG nor IgA were detected in blood or feces, respectively, of NonVx-Ch and NonVx-NonCh groups prior to or post vaccinations. Both Vx-Ch and NonVx-Ch animals shed detectable levels of challenge strain during the course of the study. Despite the lack of protection with the vaccine formulations there were detectable shifts in the microbiota of vaccinated animals before and after challenge with E. coli O157:H7.

Validity of a single antibody-based lateral flow immunoassay depending on graphene oxide for highly sensitive determination of E. coli O157:H7 in minced beef and river water

Considering the health risks of E. coli O157:H7 presence in food and water, an affordable and highly sensitive detection method is crucial. Herein, we report the first use of a single antibody-based fluorescent lateral flow immunoassay (FLFIA) depending on non-radiative energy transfer between graphene oxide and quantum dots for determination of E. coli O157:H7 in beef and river water. FLFIA showed a high sensitivity rate thousand-fold better than the conventional lateral flow (LF). In inoculated minced beef and river water samples, the limits of detection were 178 and 133 CFU g^-1 or mL^-1, respectively. Besides, it presented a high selectivity in the presence of other possible interfering bacteria. The single antibody approach reduced the assay cost to 60% less than the conventional LF. Alongside, the results could be read by portable LF readers or smartphones. These advantages offer FLFIA as a promising technology for pathogen detection in food and water.

Universal and reusable hapten/antibody-mediated portable optofluidic immunosensing platform for rapid on-site detection of pathogens

A universal and reusable hapten-antibody-mediated portable optofluidic immunosensing platform (OIP) was developed for rapid on-site detection of pathogens. By using Escherichia coli O157:H7 (E. coli O157:H7) and bisphenol A-Bovine serum albumin (BPA-BSA)/anti-BPA antibody as a model pathogen and a mediated hapten-antibody, respectively, a novel immunoassay mechanism was proposed to detect pathogens. The BPA-BSA-modified immunosensor and E. coli O157:H7 were initially saturated with anti-BPA antibodies (mouse IgG) and anti-E. coli O157:H7 antibodies (mouse IgG), respectively. Then, the fluorescence-labeled secondary antibodies (goat anti-mouse IgG antibody) were incubated with E. coli O157:H7 with their antibodies. Next, the mixture was introduced into the immunosensor surface bound to the anti-BPA antibodies. A high concentration of E. coli O157:H7 in the sample reduced the number of fluorescence-labeled secondary antibodies bound to the immunosensor surface, thus resulting in the detection of low fluorescence signals. Under optimized conditions, the hapten-antibody-mediated OIP system exhibited a detection limit of 8 cfu/mL E. coli O157:H7 after concentrating 100 times by using centrifugation, and a test cycle, including prereaction, detection, and regeneration, was less than 1 h. The robustness of the hapten-carrier protein-modified immunosensor surface allowed multiple pathogen immunoassays. The proposed strategy demonstrated good recovery, precision, and accuracy through the evaluation of the spiked water samples. We expect that the new platform can be readily used for the detection of other pathogens in a variety of application fields ranging from environmental monitoring and food safety to medical diagnosis.

Survival and interaction of Escherichia coli O104:H4 on Arabidopsis thaliana and lettuce (Lactuca sativa) in comparison to E. coli O157:H7: Influence of plant defense response and bacterial capsular polysaccharide

Shiga toxin-producing Escherichia coli (STEC) has been associated with illnesses and outbreaks linked to fresh vegetables, prompting a growing public health concern. Most studies regarding interactions of STEC on fresh produce focused on E. coli O157:H7. Limited information is available about survival or fitness of E. coli O104:H4, non-O157 pathogen that was linked to one of the largest outbreaks of hemolytic uremic syndrome in 2011. In this study, survival of E. coli O104:H4 was evaluated on Arabidopsis thaliana plant and lettuce for 5 days compared with E. coli O157:H7, and expression of pathogenesis-realted gene (PR1; induction of plant defense response) was examined by reverse transcription quantitative PCR, and potential influence of capsular polysaccharide (CPS) on the bacterial fitness on plant was investigated. Populations of E. coli O104:H4 strains (RG1, C3493, and LpfA) on Arabidopsis and lettuce were significantly (P < 0.05) greater than those of E. coli O157:H7 strains (7386 and sakai) at day 5 post-inoculation, indicating E. coli O104:H4 may have better survival ability on the plants. In addition, the E. coli O104:H4 strains produced significantly (P < 0.05) higher amounts of CPS compared with the E. coli O157:H7 strains. RG1 strain (1.5-fold) initiated significantly (P < 0.05) lower expression of PR1 gene indicating induction of plant defense response compared with E. coli O157:H7 strains 7386 (2.9-fold) and sakai (2.7-fold). Collectively, the results in this study suggests that different level of CPS production and plant defense response initiated by each STEC strain might influence the bacterial survival or persistence on plants. The present study provides better understanding of survival behavior of STEC, particularly E. coli O104:H4, using a model plant and vegetable under pre-harvest conditions with plant defense response.

Genetic variation in humoral response to an Escherichia coli O157:H7 vaccine in beef cattle

Individuals often respond differently to the same vaccine; some of this variation may be caused by genetic differences among animals. Our objective was to estimate heritability and identify genomic regions associated with humoral response to an Escherichia coli O157:H7 vaccine in beef cattle. Crossbred beef cattle (n = 651) were vaccinated with a commercially available E. coli O157:H7 vaccine. Serum was collected at time of initial vaccination (d 0), booster (d 21), and d 56 after initial vaccination. Total antibodies specific to siderophore receptor and porin proteins in the vaccine were quantified by enzyme-linked immunosorbent assay. Genomic DNA was isolated from whole blood and genotyped with the bovine GeneSeek Genomic Profiler-High Density 78K or 26K Single Nucleotide Polymorphism BeadChip and imputed to 777,000 SNP genotypes. Heritability was estimated by restricted maximum likelihood (REML) using both 1) pedigree and 2) genomic relationships among individuals. Fixed effects were contemporary group, calf age, sex, principal components from SNP genotype data, and pedigree-derived heterozygosity effects. Additive and dominance effects of SNPs were estimated individually while accounting for contemporary group, sex, and the top 20 principal components calculated from the genomic relationship matrix. Heritability of initial response to vaccination (d 21 –d 0) was 0.10 ± 0.175 using pedigree relationships and 0.14 ± 0.149 using genomic relationships, but neither estimate was statistically different from zero. Heritability of booster (d 56 –d 21) and overall (d 56 –d 0) responses were low and not statistically significant from zero. There were no clusters of linked SNP associated with vaccine response, but eight regionally isolated SNPs were significantly associated with initial or overall response to vaccination. Regional genetic variation for initial response to an E. coli O157:H7 vaccine was observed, although overall heritability of this response was not statistically significant from zero.

Influence of surface polysaccharides of Escherichia coli O157:H7 on plant defense response and survival of the human enteric pathogen on Arabidopsis thaliana and lettuce (Lactuca sativa)

This study aimed to determine the influence of bacterial surface polysaccharides (cellulose, colanic acid, and lipopolysaccharide; LPS) on the colonization or survival of Escherichia coli O157:H7 on plants and the plant defense response. Survival of E. coli O157:H7 were evaluated on Arabidopsis thaliana and romaine lettuce as a model plant and an edible crop (leafy vegetable), respectively. The population of the wild-type strain of E. coli O157:H7 on Arabidopsis plants and lettuce was significantly (P < 0.05) greater compared with the colanic acid-deficient and LPS-truncated mutants on day 1 and day 5 post-inoculation. This result indicates that colanic acid and LPS structures may contribute to the ability of bacterial survival or persistence on plants. The wild-type strain of E. coli O157:H7 produced approximately twice the amount (P < 0.05) of capsular polysaccharide (CPS) than the colanic acid and LPS-truncated mutants. The significantly lower production of CPS was associated with significantly greater (2-fold) expression of pathogenesis-related gene (PR1) compared with the wild-type and cellulose-deficient mutant (P < 0.05). Collectively, the results of this study may suggest that specific surface polysaccharides of E. coli O157:H7 differentially induce the plant defense response, consequently affecting the survival of the human pathogen on plants. The survival and persistence of E. coli O157:H7 was similar on Arabidopsis and lettuce regardless of day post-inoculation.

A recombinant O-polysaccharide-protein conjugate approach to develop highly specific monoclonal antibodies to Shiga toxin-producing Escherichia coli O157 and O145 serogroups

Shiga toxin-producing Escherichia coli (STEC) is the major etiologic agent of hemolytic-uremic syndrome (HUS). The high rate of HUS emphasizes the urgency for the implementation of primary prevention strategies to reduce its public health impact. Argentina shows the highest rate of HUS worldwide, being E. coli O157 the predominant STEC-associated HUS serogroup (>70%), followed by E. coli O145 (>9%). To specifically detect these serogroups we aimed at developing highly specific monoclonal antibodies (mAbs) against the O-polysaccharide (O-PS) section of the lipopolysaccharide (LPS) of the dominant STEC-associated HUS serogroups in Argentina. The development of hybridomas secreting mAbs against O157 or O145 was carried out through a combined immunization strategy, involving adjuvated-bacterial immunizations followed by immunizations with recombinant O-PS-protein conjugates. We selected hybridoma clones that specifically recognized the engineered O-PS-protein conjugates of O157 or O145 serogroups. Indirect ELISA of heat-killed bacteria showed specific binding to O157 or O145 serogroups, respectively, while no cross-reactivity with other epidemiological important STEC strains, Brucella abortus, Salmonella group N or Yersinia enterocolitica O9 was observed. Western blot analysis showed specific recognition of the sought O-PS section of the LPS by all mAbs. Finally, the ability of the developed mAbs to bind the surface of whole bacteria cells was confirmed by flow cytometry, confocal microscopy and agglutination assays, indicating that these mAbs present an exceptional degree of specificity and relative affinity in the detection and identification of E. coli O157 and O145 serogroups. These mAbs may be of significant value for clinical diagnosis and food quality control applications. Thus, engineered O-PS specific moieties contained in the recombinant glycoconjugates used for combined immunization and hybridoma selection are an invaluable resource for the development of highly specific mAbs.

A Plant-Produced Candidate Subunit Vaccine Reduces Shedding of Enterohemorrhagic Escherichia coli in Ruminants

Enterohemorrhagic Escherichia coli (EHEC) are commonly present in the gastrointestinal tract of cattle and cause serious infectious disease in humans. Immunizing cattle against EHEC is a promising strategy to decrease the risk of food contamination; however, veterinary vaccines against EHEC such as Econiche have not been widely adopted by the agricultural industry, and have been discontinued, prompting the need for more cost-effective EHEC vaccines. The objective of this project is to develop a platform to produce plant-made antigens for oral vaccination of ruminants against EHEC. Five recombinant proteins were designed as vaccine candidates and expressed transiently in Nicotiana benthamiana and transplastomically in Nicotiana tabacum. Three of these EHEC proteins, NleA, Stx2b, and a fusion of EspA accumulated when transiently expressed. Transient protein accumulation was the highest when EHEC proteins were fused to an elastin-like polypeptide (ELP) tag. In the transplastomic lines, EspA accumulated up to 479 mg kg-1 in lyophilized leaf material. Sheep that were administered leaf tissue containing recombinant EspA shed less E. coli O157:H7 when challenged, as compared to control animals. These results suggest that plant-made, transgenic EspA has the potential to reduce EHEC shedding in ruminants.

Nano-encapsulation of chicken immunoglobulin (IgY) in sodium alginate nanoparticles: In vitro characterization

Controlled delivery of therapeutic agents by alginate nanoparticles became an attractive issue in the gastric organ. Some therapeutic agents such as proteins could not tolerate in severe condition in the gastrointestinal tract. In the present study, four concentrations of a specific IgY as a prophylactic agent against E. coli O157: H7 was entrapped in 0.2% w/v sodium alginate nanoparticles by ionic gelation method. Depending on the IgY concentration entrapment efficacy was 28.31-99.84%. The physicochemical and structural characteristics of free and IgY-loaded Alg NPs revealed that the individual particles exhibited a spherical shape with a diameter of 45-85 nm, and a negatively charged surface with a zeta potential value of 26-36 mV. In vitro release study showed a high significant difference of released amounts of IgY at 10% and 99.84% in simulated gastric fluid (pH 1.2) and simulated intestine fluid (pH 6.8), respectively. Also, the quality and activity of released IgY from Alg NPs not changed. The cytotoxicity of different concentrations of Alg NPs on the Vero cells was measured. Our results indicated that Alg NPs prepared from 0.2%w/v stock solution could be appropriate candidates for efficient and safe delivery of IgY through the gastrointestinal tract.

Quercetin suppresses NLRP3 inflammasome activation in epithelial cells triggered by Escherichia coli O157:H7

Inflammatory responses elicited by LRR and PYD domains-containing protein 3 (NLRP3) inflammasome is induced by a wide variety of stress signals including infectious agents and cellular disorders. E. coli O157:H7 causes serious gastrointestinal diseases that results in severe inflammation and oxidative stress, causing host cell damage. In this study, we found that E. coli O157:H7 infection induced NLRP3 assembly, caspase-1 activation and interleukin (IL)-1β and IL-18 release in Caco-2 cells. Infection also resulted in mitochondrial dysfunction with disrupted mitochondrial potential and mitochondrial complex-I activity, as well as the cytosolic release of cytochrome c and altered mitochondrial respiratory chain. The damage of mitochondria led to increased production of reactive oxygen species (ROS) and cytosolic release of mitochondrial DNA. Moreover, ROS was required for E. coli O157:H7 induced NLRP3 assembly as inhibiting mitochondrial ROS release by ROS scavengers Mito-TEMPO and N-acetylcysteine abrogated NLRP3 inflammasome activation in Caco-2 cells in response to E. coli O157:H7. Quercetin, one of the most important flavonoids in plant origin foods, had a protective role in inhibiting NLRP3 activation upon E. coli O157:H7 infection by protecting mitochondrial integrity and inhibiting mitochondrial ROS release. In addition, E. coli O157:H7 infection inhibited the host autophagy while quercetin treatment augmented autophagy activation, which further blocked ROS generation and IL-1β and IL-18 release. In summary, E. coli O157:H7 infection induced mitochondrial ROS release and NLRP3 assembly in host cells, while quercetin exerted a preventive role in host cells upon E. coli O157:H7 infection partially due to prevention of ROS production and activation of autophagy.

Efficacy of Urtoxazumab (TMA-15 Humanized Monoclonal Antibody Specific for Shiga Toxin 2) Against Post-Diarrheal Neurological Sequelae Caused by Escherichia coli O157:H7 Infection in the Neonatal Gnotobiotic Piglet Model

Enterohemorrhagic Escherichia coli (EHEC) is the most common cause of hemorrhagic colitis and hemolytic uremic syndrome in human patients, with brain damage and dysfunction the main cause of acute death. We evaluated the efficacy of urtoxazumab (TMA-15, Teijin Pharma Limited), a humanized monoclonal antibody against Shiga toxin (Stx) 2 for the prevention of brain damage, dysfunction, and death in a piglet EHEC infection model. Forty-five neonatal gnotobiotic piglets were inoculated orally with 3 × 10⁹ colony-forming units of EHEC O157:H7 strain EDL933 (Stx1⁺, Stx2⁺) when 22–24 h old. At 24 h post-inoculation, piglets were intraperitoneally administered placebo or TMA-15 (0.3, 1.0 or 3.0 mg/kg body weight). Compared to placebo (n = 10), TMA-15 (n = 35) yielded a significantly greater probability of survival, length of survival, and weight gain (p <0.05). The efficacy of TMA-15 against brain lesions and death was 62.9% (p = 0.0004) and 71.4% (p = 0.0004), respectively. These results suggest that TMA-15 may potentially prevent or reduce vascular necrosis and infarction of the brain attributable to Stx2 in human patients acutely infected with EHEC. However, we do not infer that TMA-15 treatment will completely protect human patients infected with EHEC O157:H7 strains that produce both Stx1 and Stx2.

Potential immunosuppressive effects of Escherichia coli O157:H7 experimental infection on the bovine host

BACKGROUND

Enterohaemorrhagic Escherichia coli (EHEC), like E. coli O157:H7 are frequently detected in bovine faecal samples at slaughter. Cattle do not show clinical symptoms upon infection, but for humans the consequences after consuming contaminated beef can be severe. The immune response against EHEC in cattle cannot always clear the infection as persistent colonization and shedding in infected animals over a period of months often occurs. In previous infection trials, we observed a primary immune response after infection which was unable to protect cattle from re-infection. These results may reflect a suppression of certain immune pathways, making cattle more prone to persistent colonization after re-infection. To test this, RNA-Seq was used for transcriptome analysis of recto-anal junction tissue and ileal Peyer's patches in nine Holstein-Friesian calves in response to a primary and secondary Escherichia coli O157:H7 infection with the Shiga toxin (Stx) negative NCTC12900 strain. Non-infected calves served as controls.

RESULTS

In tissue of the recto-anal junction, only 15 genes were found to be significantly affected by a first infection compared to 1159 genes in the ileal Peyer's patches. Whereas, re-infection significantly changed the expression of 10 and 17 genes in the recto-anal junction tissue and the Peyer's patches, respectively. A significant downregulation of 69 immunostimulatory genes and a significant upregulation of seven immune suppressing genes was observed.

CONCLUSIONS

Although the recto-anal junction is a major site of colonization, this area does not seem to be modulated upon infection to the same extent as ileal Peyer's patches as the changes in gene expression were remarkably higher in the ileal Peyer's patches than in the recto-anal junction during a primary but not a secondary infection. We can conclude that the main effect on the transcriptome was immunosuppression by E. coli O157:H7 (Stx-) due to an upregulation of immune suppressive effects (7/12 genes) or a downregulation of immunostimulatory effects (69/94 genes) in the ileal Peyer's patches. These data might indicate that a primary infection promotes a re-infection with EHEC by suppressing the immune function.

Development of a Sandwich ELISA for EHEC O157:H7 Intimin γ1

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a zoonotic pathogen of worldwide importance that causes foodborne infections in humans. Intimin gamma 1 (intimin γ1) is one of the most important outer membrane proteins required for EHEC’s intimate adhesion to epithelial cells. Here, we generated a polyclonal antibody (pAb) and a monoclonal antibody (mAb) against intimin γ1 to develop a double antibody sandwich ELISA (DAS-ELISA) with increased sensitivity and specificity for measuring EHEC O157:H7. To achieve this goal, a rabbit pAb was used as a capture antibody, and a mouse mAb was a detection antibody. No cross-reactivity was observed with the other genera of pathogenic bacteria tested with the DAS-ELISA, which included Salmonella enteritidis, Shigella flexneri type 2, Listeria monocytogenes, Streptococcus suis type 2, and other 18 serotype E. coli. Detection limits of the DAS-ELISA were 1 × 10³ CFU/mL for EHEC O157:H7 cultures, 1 × 10⁴ CFU/g before enrichment, and 1 × 10² CFU/g after enrichment of contaminated samples. Field samples (n = 498) were tested using a previously established duplex-PCR method and compared to our DAS-ELISA. The DAS-ELISA had a specificity of 94.4%, a sensitivity of 91.5% and accuracy of 94.0% compared with duplex-PCR. The DAS-ELISA developed here can be applied to EHEC O157:H7 quantification in food, animal, and environmental samples.

Effects of Rhodomyrtus tomentosa Extract on Killing Activity of Human Neutrophils and Membrane Integrity of Enterohaemorrhagic Escherichia coli O157:H7

Enterohaemorrhagic Escherichia coli (E. coli) O157:H7 is one of the most virulent causative agents of foodborne disease. Use of antibiotics for the treatment against E. coli O157:H7 infection leads to hemolytic uremic syndrome. The present study evaluated the potential of ethanolic leaf extract of a medicinal plant, Rhodomyrtus tomentosa in enhancing the killing activity of human neutrophils against E. coli O157:H7. In addition, the effects of the extract on membrane permeability of the organisms were studied. In the killing assay, percentage survival of the bacterial cells after being exposed to human neutrophils in the presence of various concentrations of the extract were determined. At 45 min, percentage survival of E. coli O157:H7 and E. coli ATCC 25922 after treated with neutrophils in the presence of the extract at 125-250 µg/mL was 58.48%-50.28% and 69.13%-35.35%, respectively. Furthermore, upon treatment with R. tomentosa at 250 µg/mL uptake of crystal violet by E. coli O157:H7 and E. coli ATCC 25922 was increased to 40.07% and 36.16%, respectively. Therefore, it is suggested that the extract exhibited dual effects as immunostimulant and membrane permeabilizing agent perhaps resulted in enhancing the killing activity of neutrophils against the organisms.

Rapid Detection of Escherichia coli O157 and Shiga Toxins by Lateral Flow Immunoassays

Shiga toxin-producing Escherichia coli O157:H7 (STEC) cause food-borne illness that may be fatal. STEC strains enumerate two types of potent Shiga toxins (Stx1 and Stx2) that are responsible for causing diseases. It is important to detect the E. coli O157 and Shiga toxins in food to prevent outbreak of diseases. We describe the development of two multi-analyte antibody-based lateral flow immunoassays (LFIA); one for the detection of Stx1 and Stx2 and one for the detection of E. coli O157 that may be used simultaneously to detect pathogenic E. coli O157:H7. The LFIA strips were developed by conjugating nano colloidal gold particles with monoclonal antibodies against Stx1 and Stx2 and anti-lipid A antibodies to capture Shiga toxins and O157 antigen, respectively. Our results indicate that the LFIA for Stx is highly specific and detected Stx1 and Stx2 within three hours of induction of STEC with ciprofloxacin at 37 °C. The limit of detection for E. coli O157 LFIA was found to be 10⁵ CFU/mL in ground beef spiked with the pathogen. The LFIAs are rapid, accurate and easy to use and do not require sophisticated equipment or trained personnel. Following the assay, colored bands on the membrane develop for end-point detection. The LFIAs may be used for screening STEC in food and the environment.

Comparative Transcriptomic Analysis of Rectal Tissue from Beef Steers Revealed Reduced Host Immunity in Escherichia coli O157:H7 Super-Shedders

Super-shedder cattle are a major disseminator of E. coli O157:H7 into the environment, and the terminal rectum has been proposed as the primary E. coli O157:H7 colonization site. This study aimed to identify host factors that are associated with the super-shedding process by comparing transcriptomic profiles in rectal tissue collected from 5 super-shedder cattle and 4 non-shedder cattle using RNA-Seq. In total, 17,859 ± 354 genes and 399 ± 16 miRNAs were detected, and 11,773 genes were expressed in all animals. Fifty-eight differentially expressed (DE) genes (false discovery rate < 0.05) including 11 up-regulated and 47 down-regulated (log 2 (fold change) ranged from -5.5 to 4.2), and 2 up-regulated DE miRNAs (log 2 (fold change) = 2.1 and 2.5, respectively) were identified in super-shedders compared to non-shedders. Functional analysis of DE genes revealed that 31 down-regulated genes were potentially associated with reduced innate and adaptive immune functions in super-shedders, including 13 lymphocytes membrane receptors, 3 transcription factors and 5 cytokines, suggesting the decreased key host immune functions in the rectal tissue of super-shedders, including decreased quantity and migration of immune cells such as lymphocytes, neutrophils and dendritic cells. The up-regulation of bta-miR-29d-3p and the down regulation of its predicted target gene, regulator of G-protein signaling 13, suggested a potential regulatory role of this miRNA in decreased migration of lymphocytes in super-shedders. Based on these findings, the rectal tissue of super-shedders may inherently exhibit less effective innate and adaptive immune protection. Further study is required to confirm if such effect on host immunity is due to the nature of the host itself or due to actions mediated by E. coli O157:H7.

Fecal diagnostics in combination with serology: best test to establish STEC-HUS

BACKGROUND

In the majority of pediatric patients, the hemolytic-uremic syndrome (HUS) is caused by an infection with Shiga toxin-producing Escherichia coli (STEC), mostly serotype O157. It is important to discriminate between HUS caused by STEC and complement-mediated HUS (atypical HUS) due to differences in treatment and outcome. As STEC and its toxins can only be detected in the patient's stool for a short period of time after disease onset, the infectious agent may go undetected using only fecal diagnostic tests. Serum antibodies to lipopolysaccharide (LPS) of STEC persist for several weeks and may therefore be of added value in the diagnosis of STEC.

METHODS

All patients with clinical STEC-HUS who were treated at Radboud University Medical Center between 1990 and 2014 were included in this retrospective single-center study. Clinical and diagnostic microbiological data were collected. Immunoglobulin M (IgM) antibodies against LPS of STEC serotype O157 were detected by a serological assay (ELISA).

RESULTS

Data from 65 patients weres available for analysis. Fecal diagnostic testing found evidence of an STEC infection in 34/63 patients (54 %). Serological evidence of STEC O157 was obtained in an additional 16 patients. This is an added value of 23 % (p < 0.0001) when the serological antibody assay is used in addition to standard fecal diagnostic tests to confirm the diagnosis STEC-HUS. This added value becomes especially apparent when the tests are performed more than 7 days after the initial manifestation of the gastrointestinal symptoms.

CONCLUSIONS

The serological anti-O157 LPS assay clearly makes a positive contribution when used in combination with standard fecal diagnostic tests to diagnose STEC-HUS and should be incorporated in clinical practice.

Antibody Microarray for E. coli O157:H7 and Shiga Toxin in Microtiter Plates

Antibody microarray is a powerful analytical technique because of its inherent ability to simultaneously discriminate and measure numerous analytes, therefore making the technique conducive to both the multiplexed detection and identification of bacterial analytes (i.e., whole cells, as well as associated metabolites and/or toxins). We developed a sandwich fluorescent immunoassay combined with a high-throughput, multiwell plate microarray detection format. Inexpensive polystyrene plates were employed containing passively adsorbed, array-printed capture antibodies. During sample reaction, centrifugation was the only strategy found to significantly improve capture, and hence detection, of bacteria (pathogenic Escherichia coli O157:H7) to planar capture surfaces containing printed antibodies. Whereas several other sample incubation techniques (e.g., static vs. agitation) had minimal effect. Immobilized bacteria were labeled with a red-orange-fluorescent dye (Alexa Fluor 555) conjugated antibody to allow for quantitative detection of the captured bacteria with a laser scanner. Shiga toxin 1 (Stx1) could be simultaneously detected along with the cells, but none of the agitation techniques employed during incubation improved detection of the relatively small biomolecule. Under optimal conditions, the assay had demonstrated limits of detection of ~5.8 × 10⁵ cells/mL and 110 ng/mL for E. coli O157:H7 and Stx1, respectively, in a ~75 min total assay time.

Immune-stimulating properties of 80% methanolic extract of Ludwigia octovalvis against Shiga toxin-producing E. coli O157:H7 in Balb/c mice following experimental infection

ETHNOPHARMACOLOGICAL RELEVANCE

Ludwigia octovalvis is an aquatic plant widely distributed throughout the tropical and sub-tropical regions. It is commonly consumed as a health drink and traditionally used for treating various ailments such as dysentery, diarrhea, diabetes, nephritisn and headache. No information is available on its in vivo antibacterial activity against an important foodborne pathogen, Shiga toxin producing Escherichia coli O157:H7.

MATERIALS AND METHODS

Male Balb/c mice were orally administered with the extract at doses of 200 or 400mg/kg body weight for one week before the infection with E. coli O157:H7 and continued for 14 consecutive days after infection. Serum antibody (IgA, IgG and IgM) levels were quantified at days 7 and 14 post-challenge by an ADVIA(®) 2400 Clinical Chemistry Auto Analyzer. Nitroblue tetrazolium (NBT) and Ceruloplasmin, as nonspecific immune parameters, were determined enzymatically.

RESULTS

A significant increase (p<0.05) in IgA serum level was indicated on the 7th day post-challenge with the pathogen in the experimental group received 400mg/kg of the extract in comparison with other groups. Total IgA serum levels on day 7 post-challenge in groups of PBS negative control, E. coli O157:H7 positive control, E. coli O157:H7+200mg/kg extract group and E. coli O157:H7+400mg/kg extract group were 709.4 ± 149.6, 1655.8 ± 139.7, 1728.6 ± 64.3 and 1971.4 ± 135.6 µg/ml, respectively. Serum IgG and IgM did not significantly change among different groups. The extract administered orally to infected Balb/c mice did not affect the NBT as well as ceruloplasmin levels.

CONCLUSIONS

The extract of L. octovalvis contains biologically active principles which increased systemic immune response to E. coli O157:H7 via potentiating the synthesis of IgA antibodies.

Electrochemical Impedance Immunosensor Based on Self-Assembled Monolayers for Rapid Detection of Escherichia coli O157:H7 with Signal Amplification Using Lectin

Escherichia coli O157:H7 is a predominant foodborne pathogen with severe pathogenicity, leading to increasing attention given to rapid and sensitive detection. Herein, we propose an impedance biosensor using new kinds of screen-printed interdigitated microelectrodes (SPIMs) and wheat germ agglutinin (WGA) for signal amplification to detect E. coli O157:H7 with high sensitivity and time-efficiency. The SPIMs integrate the high sensitivity and short response time of the interdigitated electrodes and the low cost of the screen-printed electrodes. Self-assembling of bi-functional 3-dithiobis-(sulfosuccinimidyl-propionate) (DTSP) on the SPIMs was investigated and was proved to be able to improve adsorption quantity and stability of biomaterials. WGA was further adopted to enhance the signal taking advantage of the abundant lectin-binding sites on the bacteria surface. The immunosensor exhibited a detection limit of 10² cfu·mL⁻¹, with a linear detection range from 10² to 10⁷ cfu·mL⁻¹ (r² = 0.98). The total detection time was less than 1 h, showing its comparable sensitivity and rapid response. Furthermore, the low cost of one SPIM significantly reduced the detection cost of the biosensor. The biosensor may have great promise in food safety analysis and lead to a portable biosensing system for routine monitoring of foodborne pathogens.

The Escherichia coli O157:H7 cattle immunoproteome includes outer membrane protein A (OmpA), a modulator of adherence to bovine rectoanal junction squamous epithelial (RSE) cells

Building on previous studies, we defined the repertoire of proteins comprising the immunoproteome (IP) of Escherichia coli O157:H7 (O157) cultured in DMEM supplemented with norepinephrine (O157 IP), a β-adrenergic hormone that regulates E. coli O157 gene expression in the gastrointestinal tract, using a variation of a novel proteomics-based platform proteome mining tool for antigen discovery, called "proteomics-based expression library screening" (PELS; Kudva et al., 2006). The E. coli O157 IP (O157-IP) comprised 91 proteins, and included those identified previously using proteomics-based expression library screening, and also proteins comprising DMEM and bovine rumen fluid proteomes. Outer membrane protein A (OmpA), a common component of the above proteomes, and reportedly a contributor to E. coli O157 adherence to cultured HEp-2 epithelial cells, was interestingly found to be a modulator rather than a contributor to E. coli O157 adherence to bovine rectoanal junction squamous epithelial cells. Our results point to a role for yet to be identified members of the O157-IP in E. coli O157 adherence to rectoanal junction squamous epithelial cells, and additionally implicate a possible role for the outer membrane protein A regulator, TdcA, in the expression of such adhesins. Our observations have implications for the development of efficacious vaccines for preventing E. coli O157 colonization of the bovine gastrointestinal tract.

Optimizing the Protection of Cattle against Escherichia coli O157:H7 Colonization through Immunization with Different Combinations of H7 Flagellin, Tir, Intimin-531 or EspA

Enterohemorrhagic Escherichia coli (EHEC) are important human pathogens, causing hemorrhagic colitis and hemolytic uraemic syndrome in humans. E. coli O157:H7 is the most common serotype associated with EHEC infections worldwide, although other non-O157 serotypes cause life-threatening infections. Cattle are a main reservoir of EHEC and intervention strategies aimed at limiting EHEC excretion from cattle are predicted to lower the risk of human infection. We have previously shown that immunization of calves with recombinant versions of the type III secretion system (T3SS)-associated proteins EspA, intimin and Tir from EHEC O157:H7 significantly reduced shedding of EHEC O157 from experimentally-colonized calves, and that protection could be augmented by the addition of H7 flagellin to the vaccine formulation. The main aim of the present study was to optimize our current EHEC O157 subunit vaccine formulations by identifying the key combinations of these antigens required for protection. A secondary aim was to determine if vaccine-induced antibody responses exhibited cross-reactive potential with antigens from other EHEC serotypes. Immunization with EspA, intimin and Tir resulted in a reduction in mean EHEC O157 shedding following challenge, but not the mean proportion of calves colonized. Removal of Tir resulted in more prolonged shedding compared with all other groups, whereas replacement of Tir with H7 flagellin resulted in the highest levels of protection, both in terms of reducing both mean EHEC O157 shedding and the proportion of colonized calves. Immunization of calves with recombinant EHEC O157 EspA, intimin and Tir resulted in the generation of antibodies capable of cross-reacting with antigens from non-O157 EHEC serotypes, suggesting that immunization with these antigens may provide a degree of cross-protection against other EHEC serotypes. Further studies are now required to test the efficacy of these vaccines in the field, and to formally test the cross-protective potential of the vaccines against other non-O157 EHEC.

Hierarchical Flowerlike Gold Nanoparticles Labeled Immunochromatography Test Strip for Highly Sensitive Detection of Escherichia coli O157:H7

Gold nanoparticles (AuNPs) labeled lateral-flow test strip immunoassay (LFTS) has been widely used in biomedical, feed/food, and environmental analysis fields. Conventional ILFS assay usually uses spherical AuNPs as labeled probes and shows low detection sensitivity, which further limits its widespread practical application. Unlike spherical AuNP used as labeled probe in conventional ILFS, in our present study, a hierarchical flowerlike AuNP specific probe was designed for LFTS and further used to detect Escherichia coli O157:H7 (E. coli O157:H7). Three types of hierarchical flowerlike AuNPs, such as tipped flowerlike, popcornlike, and large-sized flowerlike AuNPs were synthesized in a one-step method. Compared with other two kinds of Au particles, tipped flowerlike AuNPs probes for LFTS particularly exhibited highly sensitive detection of E. coli O157:H7. The remarkable improvement of detection sensitivity of tipped flowerlike AuNPs probes can be achieved even as low as 10(3) colony-forming units (CFU)/mL by taking advantages of its appropriate size and hierarchical structures, which is superior over the detection performance of conventional LFTS. Using this novel tipped flower AuNPs probes, quantitative detection of E. coli O157:H7 can be obtained partially in a wide concentration range with good repeatability. This hierarchical tipped flower-shaped AuNPs probe for LFTS is promising for the practical applications in widespread analysis fields.

Clinical Studies of Escherichia coli O157:H7 Conjugate Vaccines in Adults and Young Children

Pediatric immunization has been the most effective measure to prevent and reduce the burden of infectious diseases in children. The recent inclusion of pneumococcal and meningococcal polysaccharide conjugates in infant immunization further reinforces their importance. Currently there is no human vaccine against enterohemorrhagic Escherichia coli (EHEC) infections. This review focuses on the human EHEC vaccine that has been studied clinically, in particular, the polysaccharide conjugate against E. coli O157. The surface polysaccharide antigen, O-specific polysaccharide, was linked to rEPA, recombinant exotoxin A of Pseudomonas aeruginosa. In adults and children 2 to 5 years old, O157-rEPA conjugates, shown to be safe, induced high levels of antilipopolysaccharide immunoglobulin G with bactericidal activities against E. coli O157, a functional bioassay that mimics the killing of inoculum in vivo. A similar construct using the B subunit of Shiga toxin (Stx) 1 as the carrier protein elicited both bactericidal and toxin-neutralizing antibodies in mice. So far there is no clinical study of Stx-based human vaccine. Passive immunization of Stx-specific antibodies with humanized, chimeric, or human monoclonal antibodies, produced in transgenic mice, showed promising data in animal models and offered high prospects. Demonstrations of their safety and effectiveness in treating hemolytic-uremic syndrome or patients with EHEC infections are under way, and results are much anticipated. For future development, other virulence factors such as the nontoxic Stx B subunit or intimin should be included, either as carrier protein in conjugates or as independent components. The additional antigens from O157 may provide broader coverage to non-O157 Stx-producing E. coli and facilitate both preventive and therapeutic treatment.

Glycoconjugate vaccine containing Escherichia coli O157:H7 O-antigen linked with maltose-binding protein elicits humoral and cellular responses

Glycoconjugate is one of the most efficacious and safest vaccines against bacterial pathogens. Previous studies of glycoconjugates against pathogen E. coli O157:H7 focused more on the humoral responses they elicited. However, little was known about their cellular responses. In this study, we exploited a novel approach based on bacterial protein N-linked glycosylation system to produce glycoconjugate containing Escherichia coli O157:H7 O-antigen linked with maltose-binding protein and examined its humoral and cellular responses in BALB/c mice. The transfer of E. coli O157:H7 O-antigen to MBP was confirmed by western blot and MALDI-TOF MS. Mice injected with glycoconjugate O-Ag-MBP elicited serum bactericidal antibodies including anti-E. coli O157:H7 O-antigen IgG and IgM. Interestingly, O-Ag-MBP also stimulated the secretion of anti-E. coli O157:H7 O-antigen IgA in intestine. In addition, O-Ag-MBP stimulated cellular responses by recruiting Th1-biased CD4+ T cells, CD8+ T cells. Meanwhile, O-Ag-MBP induced the upregulation of Th1-related IFN-γ and downregulation of Th2-related IL-4, and the upregulation of IFN-γ was stimulated by MBP in a dose-dependent manner. MBP showed TLR4 agonist-like properties to activate Th1 cells as carrier protein of O-Ag-MBP. Thus, glycoconjugate vaccine E. coli O157:H7-specific O-Ag-MBP produced by bacterial protein N-linked glycosylation system was able to elicit both humoral and Th1-biased cellular responses.

Protection from hemolytic uremic syndrome by eyedrop vaccination with modified enterohemorrhagic E. coli outer membrane vesicles

We investigated whether eyedrop vaccination using modified outer membrane vesicles (mOMVs) is effective for protecting against hemolytic uremic syndrome (HUS) caused by enterohemorrhagic E. coli (EHEC) O157:H7 infection. Modified OMVs and waaJ-mOMVs were prepared from cultures of MsbB- and Shiga toxin A subunit (STxA)-deficient EHEC O157:H7 bacteria with or without an additional waaJ mutation. BALB/c mice were immunized by eyedrop mOMVs, waaJ-mOMVs, and mOMVs plus polymyxin B (PMB). Mice were boosted at 2 weeks, and challenged peritoneally with wild-type OMVs (wtOMVs) at 4 weeks. As parameters for evaluation of the OMV-mediated immune protection, serum and mucosal immunoglobulins, body weight change and blood urea nitrogen (BUN)/Creatinin (Cr) were tested, as well as histopathology of renal tissue. In order to confirm the safety of mOMVs for eyedrop use, body weight and ocular histopathological changes were monitored in mice. Modified OMVs having penta-acylated lipid A moiety did not contain STxA subunit proteins but retained non-toxic Shiga toxin B (STxB) subunit. Removal of the polymeric O-antigen of O157 LPS was confirmed in waaJ-mOMVs. The mice group vaccinated with mOMVs elicited greater humoral and mucosal immune responses than did the waaJ-mOMVs and PBS-treated groups. Eyedrop vaccination of mOMVs plus PMB reduced the level of humoral and mucosal immune responses, suggesting that intact O157 LPS antigen can be a critical component for enhancing the immunogenicity of the mOMVs. After challenge, mice vaccinated with mOMVs were protected from a lethal dose of wtOMVs administered intraperitoneally, conversely mice in the PBS control group were not. Collectively, for the first time, EHEC O157-derived mOMV eyedrop vaccine was experimentally evaluated as an efficient and safe means of vaccine development against EHEC O157:H7 infection-associated HUS.

Sharp transition in the immunoimmobilization of E. coli O157:H7

This work focuses on immobilization of living enterohemorrhagic Escherichia coli O157:H7 on a gold surface as a function of the concentration of antibody tethered to the surface in the physiological environment of the organisms. Experiments are conducted using antibodies raised against bacterial surface lipopolysaccharides (LPS) tethered to gold-coated silicon wafers at surface concentrations spanning a range from submonolayers of antibodies to full coverage, an estimated 1 antibody per ∼100 nm(2). A careful optimization of surface chemistry is conducted to obtain the most efficient tethering of the antibodies to the surface. The mechanism of immobilizing the bacteria is antibody-antigen interactions between the tethered antibodies on the surface and the bacterial surface LPS firmly attached to the bacteria. This type of attachment is known as immunoimmobilization. The experiments suggest no noticeable bacterial attachment until the surface antibody concentration reaches ∼70% of a full monolayer of coverage. Above this critical antibody density, a sharp increase in immunoimmobilized bacteria is observed as they populate nearly 80% to 100% of the available surface area, reaching ∼1.2 cells/10 μm(2). This sharp increase in population is tentatively explained in terms of the minimum number of antibody-antigen interactions required per bacterium to immobilize the cell. This critical number is estimated to be ∼6000-8000 antibodies per bacterium (having a 1 μm(2) footprint on the surface) under the assumption that a full monolayer of antibodies is about 1 antibody per ∼100 nm(2). However, the large majority of the 6000-8000 antibodies are not expected to participate in antibody-antigen interactions, in that the loose LPS in solution will saturate many of these antibodies before bacteria have a chance to interact with them. Furthermore, the geometric considerations will further restrict the majority of the active antibodies from interacting with the surface antigens of the cell, reducing its effective contact area with the antibodies considerably.

Homologous and Heterologous Antibody Responses to Lipopolysaccharide after EnterohemorrhagicEscherichia coliInfection

To evaluate antibody responses against lipopolysaccharide (LPS: O157, O26, and O111) in enterohemorrhagic Escherichia coli(EHEC) infection, sera of 24 schoolchildren associated with the Morioka outbreak in 1997 and of 74 sporadic patients suspected of having EHEC infection were examined. Using a positive standard serum, quantitative evaluation of LPS antibodies by an enzyme-linked immunosorbent assay (ELISA) was established. High levels of specific IgM and IgA antibodies against homologous E. coli LPS were present in the acute period and are characteristic of EHEC. This could be used for the serological diagnosis of EHEC infection, except for early infants and the elderly. In addition to the specific homologous response, multiple antibody responses against different serotypes other than those isolated were demonstrated in many cases by qualitative analysis using Western blotting.

A one-step homogeneous sandwich immunosensor for Salmonella detection based on magnetic nanoparticles (MNPs) and quantum Dots (QDs)

Simple immuno-magnetic separation tandem fluorescent probes based on quantum dots-antibody (QDs-Ab) were developed to detect Salmonella with sensitivity of 500 cfu mL-1. With two monoclonal antibodies, which recognize different antigenic determinant on the surface of Salmonella, we prepared antibody-coated magnetic nanoparticles (MNPs) and conjugates of QDs-Ab. The immune-magnetic beads were verified with high enrichment efficiency for Salmonella (90%). A sandwich structure formed if the Salmonella solution was mixed together with immune-beads and QDs-Ab, and the fluorescent single from QDs was related to the amount of Salmonella. A linear response between fluorescence intensity and various concentrations of Salmonella (2.5 × 103 to 1.95 × 108 cfu mL-1) were observed with this proposed method. The total assay time for Salmonella was 30 min, and no cross-reaction to other microbial strains, such as Staphylococcus aureus, Escherichia coli (E. coli) and Escherichia coli O157:H7 (E. coli O157:H7), were found using this detection system. All our results showed that the simple homogeneous immunoassay could be applied in Salmonella screening without time-consuming extra-enrichment of bacteria.

Quantum dot enabled detection of Escherichia coli using a cell-phone

We report a cell-phone based Escherichia coli (E. coli) detection platform for screening of liquid samples. In this compact and cost-effective design attached to a cell-phone, we utilize anti-E. coli O157:H7 antibody functionalized glass capillaries as solid substrates to perform a quantum dot based sandwich assay for specific detection of E. coli O157:H7 in liquid samples. Using battery-powered inexpensive light-emitting-diodes (LEDs) we excite/pump these labelled E. coli particles captured on the capillary surface, where the emission from the quantum dots is then imaged using the cell-phone camera unit through an additional lens that is inserted between the capillary and the cell-phone. By quantifying the fluorescent light emission from each capillary tube, the concentration of E. coli in the sample is determined. We experimentally confirmed the detection limit of this cell-phone based fluorescent imaging and sensing platform as ∼5 to 10 cfu mL(-1) in buffer solution. We also tested the specificity of this E. coli detection platform by spiking samples with different species (e.g., Salmonella) to confirm that non-specific binding/detection is negligible. We further demonstrated the proof-of-concept of our approach in a complex food matrix, e.g., fat-free milk, where a similar detection limit of ∼5 to 10 cfu mL(-1) was achieved despite challenges associated with the density of proteins that exist in milk. Our results reveal the promising potential of this cell-phone enabled field-portable and cost-effective E. coli detection platform for e.g., screening of water and food samples even in resource limited environments. The presented platform can also be applicable to other pathogens of interest through the use of different antibodies.

pH effect on protein G orientation on gold surfaces and characterization of adsorption thermodynamics

The pH effect on adsorbed antibody-binding protein (protein G) orientation on gold (Au) and its adsorption thermodynamic characteristics were investigated using quartz crystal microbalance (QCM) and X-ray photoelectron spectroscopy (XPS). The adsorbed protein G orientation was measured by binding response of two antibody-antigen systems: the model bovine serum albumin (BSA) and the foodborne pathogen E. coli O157:H7. Surface coverage was not significantly affected by pH, but its orientation was. The most properly oriented protein G for antibody binding was achieved at near-neutral pH. Adsorption was verified by XPS measurements using nitrogen (N) 1s, oxygen (O) 1s, and Au 4p peak heights. Adsorption energetics were determined by van't Hoff and Langmuir kinetic analyses of adsorption data obtained at 296, 303, and 308 K. Large characteristic entropy change of protein adsorption was observed (ΔS° = 0.52 ± 0.01 kcal/mol·K). The adsorption process was not classical physisorption but exhibited chemisorption characteristics based on significant enthalpy change (ΔH° = -25 ± 6 kcal/mol).

Identifying mechanisms by which Escherichia coli O157:H7 subverts interferon-γ mediated signal transducer and activator of transcription-1 activation

Enterohemorrhagic Escherichia coli serotype O157:H7 is a food borne enteric bacterial pathogen that causes significant morbidity and mortality in both developing and industrialized nations. E. coli O157:H7 infection of host epithelial cells inhibits the interferon gamma pro-inflammatory signaling pathway, which is important for host defense against microbial pathogens, through the inhibition of Stat-1 tyrosine phosphorylation. The aim of this study was to determine which bacterial factors are involved in the inhibition of Stat-1 tyrosine phosphorylation. Human epithelial cells were challenged with either live bacteria or bacterial-derived culture supernatants, stimulated with interferon-gamma, and epithelial cell protein extracts were then analyzed by immunoblotting. The results show that Stat-1 tyrosine phosphorylation was inhibited by E. coli O157:H7 secreted proteins. Using sequential anion exchange and size exclusion chromatography, YodA was identified, but not confirmed to mediate subversion of the Stat-1 signaling pathway using isogenic mutants. We conclude that E. coli O157:H7 subverts Stat-1 tyrosine phosphorylation in response to interferon-gamma through a still as yet unidentified secreted bacterial protein.

Wide distribution of O157-antigen biosynthesis gene clusters in Escherichia coli

Most Escherichia coli O157-serogroup strains are classified as enterohemorrhagic E. coli (EHEC), which is known as an important food-borne pathogen for humans. They usually produce Shiga toxin (Stx) 1 and/or Stx2, and express H7-flagella antigen (or nonmotile). However, O157 strains that do not produce Stxs and express H antigens different from H7 are sometimes isolated from clinical and other sources. Multilocus sequence analysis revealed that these 21 O157:non-H7 strains tested in this study belong to multiple evolutionary lineages different from that of EHEC O157:H7 strains, suggesting a wide distribution of the gene set encoding the O157-antigen biosynthesis in multiple lineages. To gain insight into the gene organization and the sequence similarity of the O157-antigen biosynthesis gene clusters, we conducted genomic comparisons of the chromosomal regions (about 59 kb in each strain) covering the O-antigen gene cluster and its flanking regions between six O157:H7/non-H7 strains. Gene organization of the O157-antigen gene cluster was identical among O157:H7/non-H7 strains, but was divided into two distinct types at the nucleotide sequence level. Interestingly, distribution of the two types did not clearly follow the evolutionary lineages of the strains, suggesting that horizontal gene transfer of both types of O157-antigen gene clusters has occurred independently among E. coli strains. Additionally, detailed sequence comparison revealed that some positions of the repetitive extragenic palindromic (REP) sequences in the regions flanking the O-antigen gene clusters were coincident with possible recombination points. From these results, we conclude that the horizontal transfer of the O157-antigen gene clusters induced the emergence of multiple O157 lineages within E. coli and speculate that REP sequences may involve one of the driving forces for exchange and evolution of O-antigen loci.

Evaluation of different micro/nanobeads used as amplifiers in QCM immunosensor for more sensitive detection of E. coli O157:H7

Micro/nanobeads with different materials (magnetic, silica and polymer) and different sizes (diameters from 30nm to 970nm) were investigated for their use as amplifiers in a quartz crystal microbalance (QCM) immunosensor for more sensitive detection of Escherichia coli O157:H7. The micro/nanobeads were conjugated with anti-E. coli antibodies. E. coli O157:H7 cells were first captured by the first antibody immobilized on the electrode surface, and then micro/nanobeads labeled secondary antibodies attached to the cells, and finally the complexes of antibody-E. coli-antibody modified beads were formed. The results showed that antibody-labeled beads lead to signal amplification in both the change in frequency (ΔF) and the change in resistance (ΔR). Since the penetration depth of the oscillation-induced shear-waves for a ∼8MHz crystal is limited to 200nm, the interpretation of how the signal is amplified by the adsorbed particles was represented in terms of the coupled-oscillator theory. The amplification is not sensed in terms of increase in mass on the sensor surface. Amplification is sensed as a change in bacterial resonance frequency when the spheres adsorb to the bacteria. The change in the values of ΔF caused by different micro/nanobeads (amplifiers) attaching on target bacterial cells is indicative of the ratio between the resonance frequency of the absorbed bacterial-particle complex (ω(s)), and the resonance frequency of the crystal (ω).

Vaccination with type III secreted proteins leads to decreased shedding in calves after experimental infection with Escherichia coli O157

Escherichia coli O157:H7 remains a threat to humans via cattle-derived fecal contamination of food and water. Preharvest intervention strategies represent a means of reducing the pathogen burden before harvest. In this study, the efficacy of a commercially produced type III secreted protein (TTSP) vaccine was evaluated with the use of a commingled experimental calf infection model (30 placebo-treated animals and 30 vaccinates). The calves were vaccinated on days 0, 21, and 42 and infected with 10(9) colony-forming units (CFU) of E. coli O157 by oral-gastric intubation on day 56. Fecal shedding was monitored daily for 14 d. Serologic assessment revealed a robust immune response to vaccination; the serum titers of antibodies against EspA, Tir, and total TTSPs were significantly higher in the vaccinates than in the placebo-treated animals on days 21, 42, 56, and 70. Significantly less (P = 0.011) of the challenge organism was shed by the vaccinates than by the placebo-treated animals on days 3 to 10. Peak shedding occurred in both groups on days 3 to 6; during this period the vaccinates showed a mean log reduction of 1.4 (P = 0.002) and a mitigated fraction of 51%. The number of animals shedding was significantly lower among the vaccinates compared with the placebo group on days 3 to 6 (P ≤ 0.05), with a mean prevented fraction of 21%. No differences in the duration of shedding were observed. Owing to the low challenge shedding in both groups on days 11 to 14 (mean CFU/g < 10; median = 0), no significant differences were observed. These data indicate that TTSP vaccination had protective effects through significant reductions in the number of animals shedding and the number of challenge organisms shed per animal and provides evidence that TTSP vaccination is an effective preharvest intervention strategy against E. coli O157.

Immunogenicity of a plant-derived edible chimeric EspA, Intimin and Tir of Escherichia coli O157:H7 in mice

Transgenic plants offer the possibility to produce and deliver an oral immunogen on a large-scale with low production costs and minimal purification or enrichment. Cattles are important reservoirs of Escherichia coli O157:H7 and developing a specific immunity in animals would be invaluable. Intimin, Tir, and EspA proteins are the virulence factors expressed by LEE locus of enterohemorrhagic E. coli. We hypothesized that the chimeric recombinant forms of these effectors delivered as an edible-base vaccine would reduce colonization of bacteria in mice. A synthetic gene (eit) composed of espA (e), eae (i) and tir (t) attached by linkers was constructed. The gene was codon optimized and cloned into plant expression vectors adjacent to CaMV35S and FAE promoters for expression in tobacco and canola plants. Of total soluble protein 0.2% and 0.3% (in average) were detected in transgenic tobacco leaves and canola seeds respectively. Mice immunized either subcutaneously or orally with recombinant EIT and challenged with E. coli O157:H7 significantly exhibited reduced bacterial shedding. Application of transgenic plants containing trivalent immunogen is an effective tool for protection against E. coli O157:H7.

Subtractive inhibition assay for the detection of E. coli O157:H7 using surface plasmon resonance

A surface plasmon resonance (SPR) immunosensor was developed for the detection of E. coli O157:H7 by means of a new subtractive inhibition assay. In the subtractive inhibition assay, E. coli O157:H7 cells and goat polyclonal antibodies for E. coli O157:H7 were incubated for a short of time, and then the E. coli O157:H7 cells which bound antibodies were removed by a stepwise centrifugation process. The remaining free unbound antibodies were detected through interaction with rabbit anti-goat IgG polyclonal antibodies immobilized on the sensor chip using a BIAcore 3000 biosensor. The results showed that the signal was inversely correlated with the concentration of E. coli O157:H7 cells in a range from 3.0 × 10(4) to 3.0 × 10(8) cfu/mL with a detection limit of 3.0 × 10(4) cfu/mL. Compared with direct SPR by immobilizing antibodies on the chip surface to capture the bacterial cells and ELISA for E. coli O157:H7 (detection limit: both 3.0 × 10(5) cfu/mL in this paper), the detection limit of subtractive inhibition assay method was reduced by one order of magnitude. The method simplifies bacterial cell detection to protein-protein interaction, which has the potential for providing a practical alternative for the monitoring of E. coli O157:H7 and other pathogens.

Production and immunogenicity of recombinant ferric enterobactin protein (FepA)

OBJECTIVES

Ferric siderophore complexes are produced by most bacteria to acquire iron, a vital element. These complexes are transported across the outer membrane by receptor proteins commonly known as FepA (ferric enterobactin protein). In this study we attempted to evaluate the immunogenicity of the membrane protein FepA, aiming at inhibition of iron uptake to protect invasion of the host by the bacterium.

METHODS

The genomic fepA gene was amplified from Escherichia coli O157:H7. The PCR product was ligated into pET28a and was then expressed in E. coli BL21(DE3). The recombinant protein purified by nickel-nitrilotriacetic acid (Ni-NTA) affinity chromatography was injected into BALB/C mice to induce immunity. Antibody titer was determined by ELISA. Mouse groups were challenged with various doses of E. coli O157:H7, Shigella flexneri, Klebsiella pneumoniae, and Salmonella typhi to study immune response.

RESULTS

An 85-kDa recombinant protein was expressed and purified. Immunogenicity of the recombinant protein was determined by injecting BALB/C mice. The antibody produced therein could efficiently recognize and bind ferric enterobactin binding protein. Immunized mice challenged with higher doses of selected bacteria survived.

CONCLUSIONS

Significant recognition by the antibody of ferric enterobactin binding protein may lead to its application in the restriction of Enterobacteriaceae propagation.

Chemiluminescent detect of E. coli O157:H7 using immunological method based on magnetic nanoparticles

The system of chemiluminescent magnetic enzyme-linked immunoassay was developed. E. coli O157:H7 was sandwiched between rabbits anti-E. coli O157:H7 polyclonal antibody-coated magnetic nanoparticles (immunomagnetic nanoparticles or IMNPs) and mouse anti-E. coli O157:H7 monoclonal antibody. Commercial alkaline phosphatase conjugated horse anti-mouse immunoglobulin (ALP-Ab) was used to bind with the monoclonal antibody, finally the chemiluminescent signals were detected by adding 3-(2'-spiroadamantane)-4-methoxy-4-(3"-phosphoryloxy)phenyl-1,2-dioxetane (AMPPD) which was the substrate reagent of ALP. Different solvents of AMPPD were compared to get an optimal chemiluminescent signal. The effects of sodium borohydride and glycine on blocking the aldehyde groups of IMNPs were compared either, and the specificity and sensitivity of this system for detecting E. coli O157:H7 were researched. The results indicated that Tris buffer was the best solvent of AMPPD, sodium borohydride was better than glycine in blocking IMNPs, and this method was of good specificity when using E. coli Top 10F' and Vibrio cholera as negative controls. The detection limit was 10(3) cells mL(-1) when the antigen solution was 1 mL, and the procedure duration was about 3 h.

Kinetics and role of antibodies against intimin beta in colostrum and in serum from goat kids and longitudinal study of attaching and effacing Escherichia coli in goat kids

The presence of antibodies to the intimin beta-binding region (Int280-beta) of attaching and effacing Escherichia coli (AEEC) in serum from 20 goat kids from 2 herds, as well as in goat colostrum, was investigated by enzyme-linked immunosorbent assay. In addition, the onset and subsequent pattern of shedding of AEEC from the same goat kids over a 6-mo period was investigated. All the colostrum and serum samples tested contained antibodies against Int280-beta. The association between the antibody titer and the isolation of AEEC suggests that antibodies to intimin beta do not prevent colonization of the intestine by AEEC in goat kids. The AEEC were generally shed only transiently. Most AEEC isolated from the kids belonged to serogroup O26. Three isolates belonged to serogroup O157. These data show that goat kids may be a reservoir of AEEC that are potentially pathogenic for humans.

Fluorescent homogeneous immunosensors for detecting pathogenic bacteria

We developed a straightforward antibody-based assay for rapid homogeneous detection of bacteria. Our sensors utilize antibody recognizing cell-surface epitopes of the target cell. Two samples of the antibody are prepared, each labeled via nanometer size flexible linkers with short complementary oligonucleotides that are modified with fluorochromes that could participate in fluorescence resonance energy transfer (FRET). The length of the complementary oligonucleotide sequences was designed such that very little annealing occurred in the absence of the target cells. In the presence of the target cells the two labeled antibodies bind to the surface of the cell resulting in a large local concentration of the complementary oligonucleotides that are attached to the antibody. This in turn drives the annealing of the complementary oligonucleotides which brings the fluorescence probes to close proximity producing large FRET signals proportional to the amount of target cells. Long flexible linkers used to attach the oligonucleotides to the antibody enable target-induced oligonucleotide annealing even if the density of surface antigens is only modest. We used Escherichia coli 0157:H7 and Salmonella typhimurium to demonstrate that this design produced sensors exhibiting rapid response time, high specificity, and sensitivity in detecting the target bacteria.

[Detection of Escherichia coli O157:H7 with piezoelectric immunosensor based on enhancement with immuno-nanoparticles]

OBJECTIVE

We developed a sensitive method to detect Escherichia coli O157:H7 based on enhancement with immuno-nanoparticles.

METHOD

About 10 nm ultrafine immunomagnetic particles were prepared by a co-precipitation method, about 20 nm immuno-colloid-gold was prepared by sodium citrate reduction. The immunosensor was fabricated by using Protein A from Staphylococcus aureus (SPA) for the antibody immobilization. Two immuno-nanoparticles by two antibodies were used to amplify frequency changing.

RESULT

The most suitable immobilization concentration and time for SPA was 1.2 mg/mL and 40 min, and dose for the antibody was 1.0 mg/mL and 60 min. With the signal amplification of the two immuno-nanoparticles, the detection limit of E. coli O157:H7 was increased from 10(4) colony-forming units (cfu)/mL to 10(1) cfu/mL.

CONCLUSION

The prepared immuno-nanoparticles might be used to significantly amplify the frequency signal of the piezoelectric immunosensor and improve the detect sensitivity.

Bovine colostral antibody against verotoxin 2 derived from Escherichia coli O157:H7: resistance to proteases and effects in beagle dogs

A bovine colostral antibody against verotoxin (VT) 2 of Escherichia coli O157:H7 was administered orally to beagle dogs. The antibody remained in the dogs' small intestine for at least 2 h, whereas little serum antibody remained 1.5 h after administration. Furthermore, the antibody activity of secretory IgA did not change until 2 h after administration; however, the activity of IgG and IgM antibodies decreased by approximately 60% and 40% at 2 h after administration, respectively. Seven beagle dogs inoculated with Escherichia coli O157:H7 producing VT2 were administered bovine colostral antibody or bovine colostral whey without antibody. With administration of bovine colostral whey without antibody, the amount of VT2 in feces decreased gradually after administration and increased again at 5 d after inoculation, whereas bovine colostral antibody significantly reduced the amount of VT2 in feces on the day after administration. In addition, 9 beagle dogs were given bovine colostral antibody, bovine plasma antibody, or saline. The amount of VT2 in feces again decreased significantly more rapidly after administration of bovine colostral antibody than after administration of bovine plasma antibody or saline.

Enterohemorrhagic Escherichia coli O157:H7: case report

Enterohemorrhagic Escherichia coli (EHEC) is a significant bacterial pathogen of bloody diarrhea. Not only does it cause systemic complications, such as hemolytic uremic syndrome (HUS) (the most common cause of potentially preventable pediatric renal failure), but it also leads to large outbreaks of bloody diarrhea. Among EHEC serotypes that cause HUS, E. coli O157:H7 is the most common. Herein, we present the case of a young girl with E. coli O157:H7 infection and review the related literature.

Oxygen electrode-based single antibody amperometric biosensor for qualitative detection of E. coli and bacteria in water

Design and performance of an amperometric biosensor for E. coli O157:H7 that is based on a common dissolved oxygen probe is discussed. Anti-E. coli O157:H7 antibody was conjugated to horseradish peroxidase and immobilized on a nitrocellulose membrane that was placed over the oxygen probe membrane using a custom-fabricated polyvinyl chloride (PVC) insert. Upon bacterial cell binding, a decrease in enzyme activity resulted in a change in oxygen concentration that was detected with a Clark-type oxygen electrode probe. Validation experiments determined the effect of the outer membrane and insert on the Clarke electrode performance and linearity, and the effects of stirring on sensor response. The mechanism of enzymatic disruption is presumably steric hindrance due to binding of the bacterial cell and conformational change in antibody structure. Sampling various dilutions of heat-sterilized E. coli O157:H7 cells in water, as little as 50 bacterial cells/mL could be detected in approximately 20 minutes of sampling and processing procedures. Bacterial concentrations from 0 to 5000 cells/mL were tested, with 2.52 mg/L +/- 0.37 mg/L equivalents of oxygen produced from as few as 50 cells/mL, versus 6.26 +/- 0.64 mg/L when no cells were present in solution. Overall, the developed amperometric biosensor technology offered an efficient means of detection primarily due to its ease of use, cost-effectiveness, portability, and amenability to incorporation at existing water quality gaging stations.

Binding of nontarget microorganisms from food washes to anti-Salmonella and anti-E. coli O157 immunomagnetic beads: minimizing the errors of random sampling in extreme dilute systems

For most applications, 3-5 observations, or samplings (n), are utilized to estimate total aerobic plate count in an average population (μ) that is greater than about 50 cells, or colony forming units (CFU), per sampled volume. We have chosen to utilize a 6 × 6 drop plate method for bacterial colony selection because it offers the means to rapidly perform all requisite dilutions in a 96-well format and plate these dilutions on solid media using minimal materials. Besides traditional quantitative purposes, we also need to select colonies which are well-separated from each other for the purpose of bacterial identification. To achieve this goal using the drop plate format requires the utilization of very dilute solutions (μ < 10 CFUs per sampled drop). At such low CFU densities the sampling error becomes problematic. To address this issue we produced both observed and computer-generated colony count data and divided a large sample of individual counts randomly into N subsamples each with n = 2-24 observations (N × n = 360). From these data we calculated the average total mean-normalized (x⁻(tot), n = 360) deviation of the total standard deviation (s (tot)) from each jth subsample's estimate (s ( j )), which we call Δ. When either observed or computer-generated Δ values were analyzed as a function of x⁻(tot), a set of relationships (∞ ₋₂√ ⁻x(tot)) were generated which appeared to converge at an n of about 18 observations. This finding was verified analytically at even lower CFU concentrations (⁻x(tot) ≈ 1 − 10 CFUs per observation). Additional experiments using the drop plate format and n = 18 samplings were performed on food samples along with most probable number (MPN) analyses and it was found that the two enumeration methods did not differ significantly.

Avian- and mammalian-derived antibodies against adherence-associated proteins inhibit host cell colonization byEscherichia coliO157:H7

AIM

To evaluate the potential for polyclonal antibodies targeting enterohaemorrhagic Escherichia coli (EHEC) virulence determinants to prevent colonization of host cells by E. coli O157:H7.

METHODS AND RESULTS

Rats and laying hens were immunized with recombinant proteins from E. coli O157:H7, EspA, C-terminal intimin or EscF. Rat antisera (IgG) or chicken egg powders (IgY) were assessed for their ability to inhibit growth and colonization-associated processes of E. coli O157:H7. Mammalian antisera with antibodies to intimin, EspA or EscF effectively reduced adherence of the pathogen to HeLa cells (P<0.05) and prevented type III secretion of Tir. Similarly, HeLa cells treated with chicken egg powder containing antibodies against intimin or EspA were protected from EHEC adherence (P<0.05). Neither egg nor rat antibody preparations had any antibacterial effect on the growth of EHEC (P>0.05).

CONCLUSIONS

Antibody preparations targeting EHEC adherence-associated factors were effective at preventing adhesion and intimate colonization-associated events.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work indicates that immunotherapy with anti-adherence antibodies can reduce E. coli O157:H7 colonization of host cells. Passive immunization with specific antibodies may have the potential to reduce E. coli O157:H7 colonization in hosts such as cattle or humans.