Protein array consisting of sol–gel bioactive platform for detection of E. coli O157:H7☆

Flexible Electronics for Monitoring in vivo Electrophysiology and Metabolite Signals

Numerous efforts have been made to develop efficient biosensors for detecting analytes in the human body. However, biosensors are often developed on rigid materials, which limits their application on skin, organs, and other tissues in the human body where good flexibility is required. Developing flexible materials for biosensors that can be used on soft and irregularly shaped surfaces would significantly expand the clinical application of biosensors. In this review, we will provide a selective overview of recently developed flexible electronic devices and their applications for monitoring in vivo metabolite and electrophysiology signals. The article provides guidelines for the development of an in vivo signal monitoring system and emphasizes research from various disciplines for the further development of flexible electronics that can be used in more biomedical applications in the future.

Anti-Adhesive Activity of Cranberry Phenolic Compounds and Their Microbial-Derived Metabolites against Uropathogenic Escherichia coli in Bladder Epithelial Cell Cultures

Cranberry consumption has shown prophylactic effects against urinary tract infections (UTI), although the mechanisms involved are not completely understood. In this paper, cranberry phenolic compounds and their potential microbial-derived metabolites (such as simple phenols and benzoic, phenylacetic and phenylpropionic acids) were tested for their capacity to inhibit the adherence of uropathogenic Escherichia coli (UPEC) ATCC^®53503™ to T24 epithelial bladder cells. Catechol, benzoic acid, vanillic acid, phenylacetic acid and 3,4-dihydroxyphenylacetic acid showed anti-adhesive activity against UPEC in a concentration-dependent manner from 100–500 µM, whereas procyanidin A2, widely reported as an inhibitor of UPEC adherence on uroepithelium, was only statistically significant (p < 0.05) at 500 µM (51.3% inhibition). The results proved for the first time the anti-adhesive activity of some cranberry-derived phenolic metabolites against UPEC in vitro, suggesting that their presence in the urine could reduce bacterial colonization and progression of UTI.

Antiadhesion as a functional concept for protection against uropathogenic Escherichia coli: in vitro studies with traditionally used plants with antiadhesive activity against uropathognic Escherichia coli

ETHNOPHARMACOLOGICAL RELEVANCE

Investigation of medicinal plant extracts traditionally used against uncomplicated urinary tract infections (UTI) and identification of antiadhesive effects under in vitro conditions against binding of uropathogenic Escherichia coli (UPEC) on bladder cell surface.

MATERIALS AND METHODS

Literature search on traditionally used medicinal plants for UTI was performed by online data bases and standard herbal monographs. For further identification shortlisting was done by intensive evaluation of results by plausibility and phytochemical aspects. Plant material with documented antibacterial effects was not considered for further investigations. Direct cytotoxicity of EtOH-water (1:1; v/v) extracts of the shortlisted plants was investigated against UPEC strain 2980 and bladder cell line T24. Inhibition of UPEC adhesion to T24 cells was monitored either after pretreatment of bacteria or eukaryotic cells by flow cytometry.

RESULTS

Literature search on traditionally used medicinal plants for UTI resulted in 275 plant species, from which 20 were shortlisted by a validated selection process for experimental testing. While direct cytotoxicity of the extracts (1-2000 μg/mL) against UPEC and T24 cells was excluded significant antiadhesive effects were monitored for five plant extracts. Two of them, prepared from the rhizome of Agropyron repens L. and the stigmata of Zea mays L. decreased bacterial adhesion (IC(25) 630 μg/mL, IC(50) 1040 μg/mL, resp.) by interacting with bacterial outer membrane proteins, which was shown by pretreatment of UPEC. Preparations of three plant extracts from the leaves of Betula spp. (according to European pharmacopoeia 7.0), Orthosiphon stamineus BENTH. and Urtica spp. showed antiadhesive effects by interacting with T24 cells (IC(50) 415, 1330 μg/mL, resp. IC(25) 580 μg/mL). Combination of two extracts, one interacting with the bacterial surface (Zea mays L., Agropyron repens L.) and one with the eukaryotic target (Orthosiphon stamineus BENTH.) revealed synergistic effects, as shown by strongly decreased IC(50) values (131 μg/mL, 511 μg/mL, resp.).

CONCLUSIONS

Different plant extracts, traditionally used for UTI, exhibit antiadhesive effects against UPEC under in vitro conditions. Molecular targets can be different, either on the bacterial or on the host cell surface. Combination of these medicinal plants with different targets, as observed often in phytotherapy, results in synergistic effects.

Antibody detection employing sol-gel immobilized parasites

Immunofluorescence assay (IFA) and immunoperoxidase assay (IPA) are useful diagnostic techniques for specific antibody detection for different diseases. Both involve several alternatives for immobilization of cells, such as solvent or heat fixation. Non-covalent immobilization implies rigorous storage conditions at -20 degrees C to preserve the slides, and usually numerous cells are detached during the washing steps, which can lead to inconsistencies in the results. Sol-gel chemistry is usually used for coating different materials because of the mild conditions of the polymerization reaction and the ability to introduce functional groups to a wide variety of surfaces. We have developed a novel procedure for the attachment of Trypanosoma cruzi epimastigotes and Leishmania guyanensis promastigotes to a silicon oxide polymer covered glass surface. The film was prepared using standard microscope slides with tetraethoxysilane and 3-aminopropyl triethoxysilane as polymeric precursors. When acetone was used as the major coating solvent, the IFA showed the fluorescence of the attached parasites without matrix background interference. Similar results were observed when the IPA was evaluated. The sensitivity and specificity of the sol-gel immobilized parasite slides were comparable with the heat fixation technique. The performance of the coated slides was maintained for at least 2 months at 4 degrees C storage temperature. This immobilization method does not affect the molecular epitopes of the attached cells. Thus, homogeneous, ready to use, long lasting coated slides were obtained, which are appropriate for field conditions.

Sensitive reagentless electrochemical immunosensor based on an ormosil sol–gel membrane for human chorionic gonadotrophin

A new organically modified silicate (ormosil) material was synthesized as a matrix to encapsulate enzyme labeled antibody for preparation of immunosensors. The ormosil matrix was prepared by hydrolyzing tetraethyoxysilane and (3-aminopropyl)triethoxysilane in weak alkali solution. It possessed three-dimensional ordered nanoporous structure with high electrical conductivity and good mechanical stability. Its hydrophilicity provided a microenvironment for retaining the biological activity of the immobilized protein. Particularly, using horseradish peroxidase-labeled human chorionic gonadotrophin antibody (HRP-anti-hCG) as a model, the immobilized HRP showed direct electron transfer at about -35 mV with a rate constant of 15.8+/-3.8s(-1). By a simple one-step immunoreaction between human serum chorionic gonadotrophin (hCG) in sample solution and the immobilized HRP-anti-hCG, the differential pulse voltammetric peak current of HRP decreased linearly with an increasing hCG concentration from 0.5 to 50 mIU/ml with a relatively low limit of detection of 0.3 mIU/ml at 3sigma. Excellent analytical performance, fabrication reproducibility and operational stability of the proposed biosensor indicated its promising application in clinical diagnostics.

Bacteriophage-based bioluminescent bioreporter for the detection of Escherichia coli 0157:H7

The rapid detection of pathogenic bacteria in food and water is vital for the prevention of foodborne illness. In this study, the lux reporter genes were used in a new bioassay that allows pathogen monitoring without multiple sample manipulations or the addition of exogenous substrate. A recombinant phage specific for Escherichia coli 0157:H7 was constructed that, upon infection, catalyzes the synthesis of N-(3-oxohexanoyl)-L-homoserine lactone (OHHL). This phage PP01 derivative carries the luxI gene from Vibrio fischeri under the control of the phage promoter PL. OHHL produced by infected E. coli 0157:H7 induces bioluminescence in bioreporter cells carrying the V. fischeri lux operon. The ability of phage PP0-luxl to detect several strains of E. coli 0157:H7 was confirmed in a 96-well plate assay. In this assay, luxCDABE bioreporter cells capable of detecting OHHL were mixed with phage PPOI-luxl and E. coli 0157:H7, and luminescence was monitored. Reporter phages induced light in bioreporter cells within I h when exposed to 10(4) CFU/ml of E. coli 0157:H7 and were able to detect 10 CFU/ml in pure culture with a preincubation step (total detection time, 4 h). The detection method was also applied to contaminated apple juice and was able to detect 10(4) CFU/ml of E. coli 0157:H7 in 2 h after a 6-h preincubation.

Detection of Escherichia coli O157, Salmonella enterica serovar Typhimurium, and staphylococcal enterotoxin B in a single sample using enzymatic bio-nanotransduction

Enzymatic bio-nanotransduction is a biological detection scheme based on the production of nucleic acid nano-signals (RNA) in response to specific biological recognition events. In this study, we applied an enzymatic bio-nanotransduction system to the detection of important food-related pathogens and a toxin. Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and staphylococcal enterotoxin B (SEB) were chosen because of the implications of these targets to food safety. Primary antibodies to each of the targets were used to functionalize magnetic beads and produce biological recognition elements (antibodies) conjugated to nano-signal-producing DNA templates. Immunomagnetic capture that was followed by in vitro transcription of DNA templates bound to target molecules produced RNA nano-signals specific for every target in the sample. Discrimination of RNA nano-signals with a standard enzyme-linked oligonucleotide fluorescence assay provided a correlation between nano-signal profiles and target concentrations. The estimated limit of detection was 2.4 x 10(3) CFU/ml for E. coli O157:H7, 1.9 X 10(4) CFU/ml for S. enterica serovar Typhimurium, and 0.11 ng/ml for SEB with multianalyte detection in buffer. Low levels of one target were also detected in the presence of interference from high levels of the other targets. Finally, targets were detected in milk, and detection was improved for E. coli 0157 by heat treatment of the milk.

Bacterial outer membrane protein analysis by electrophoresis and microchip technology

Outer membrane proteins are indispensable components of bacterial cells and participate in several relevant functions of the microorganisms. Changes in the outer membrane protein composition might alter antibiotic sensitivity and pathogenicity. Furthermore, the effects of various factors on outer membrane protein expression, such as antibiotic treatment, mutation, changes in the environment, lipopolysaccharide modification and biofilm formation, have been analyzed. Traditionally, the outer membrane protein profile determination was performed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Converting this technique to capillary electrophoresis format resulted in faster separation, lower sample consumption and automation. Coupling capillary electrophoresis with mass spectrometry enabled the fast identification of bacterial proteins, while immediate quantitative analysis permitted the determination of up- and downregulation of certain outer membrane proteins. Adapting capillary electrophoresis to microchip format ensured a further ten- to 100-fold decrease in separation time. Application of different separation techniques combined with various sensitive detector systems has ensured further opportunities in the field of high-throughput bacterial protein analysis. This review provides an overview using selected examples of outer membrane proteins and the development and application of the electrophoretic and microchip technologies for the analysis of these proteins.

One step processing of aminofunctionalized gate oxides

A plasma discharge process has been developed that allows the growth of biosensor gate oxides with adapted surface properties for the direct application of biomolecular immobilization cascades. The process involves an accurate selection of processing conditions, mainly, low temperature evaporation of (3-aminopropyl)triethoxysilane (APTS) and dynamic power and flow conditions. Room temperature evaporation of APTS was achieved by designing a vessel with an internal capillary network. The initial high power (100 W) plasma conditions were replaced by milder molecular fragmentation (50 W, 25 W) in a pure Ar discharge. Under these conditions the thin SiO(2) layers presented graded properties with a denser layer at the Si (100) interface and a hybrid organic-inorganic structure at the surface. The chemistry of the films was analysed by Fourier transformed infrared spectroscopy (FTIR) and Rutherford backscattering spectroscopy combined with elastic recoil detection analysis (RBS, ERDA), which confirmed the presence of the SiO(2) and organic phases. Contact angle measurements indicate the higher contribution of the basic polar component to the surface free energy. Furthermore, the higher affinity of the surface towards biomolecular immobilization was confirmed by fluorescence microscopy. Finally, penetration of nitrobenzaldehyde was obtained by application of a molecular permeation method evaluated by UV-vis spectroscopy onto fused silica substrates.

Hybrid titania–aminosilane platforms evaluated with human mesenchymal stem cells

The properties of hybrid aminopropyltriethoxysilane-tetraisopropylorthotitanate (APTS-TIPT) platforms prepared by a sol-gel route have been explored, and their biocompatibility was assayed after culture of human mesenchymal stem cells (hMSCs). The organic content of this material was observed to be preferably surface-oriented as indicated by microanalytical techniques. Furthermore, the surface showed characteristic amino-silane bands when explored by Raman spectroscopy as well as indications of silane and titanate condensation. Surface activity of the amino groups was probed by ultraviolet-visible spectroscopy imine derivatization and chemical force spectroscopy, showing a pH-dependent surface charge-induced potential. hMSCs cultured onto these surfaces showed relevant differences with respect to their behavior on gelatin-coated glass plates. Even if with a lower proliferative rate than controls, the cells develop long cytosolic prolongations in osteogenic differentiation medium, thus, supporting the idea of an APTS-TIPT stimulated process.

Immunosensor for the detection of Vibrio cholerae O1 using surface plasmon resonance

An immunosensor for the detection of Vibrio cholerae O1 was developed on the basis of surface plasmon resonance (SPR). A protein G layer was fabricated by means of the chemical coupling between the free amine (-NH2) groups of protein G and the activated carboxyl groups present on a self-assembled monolayer (SAM) consisting of a mixture of 11-mercaptoundecanoic acid (MUA) and hexanethiol (molar ratio of 1:2). A monoclonal antibody, which was confirmed to be specific to V. cholera O1 by the Western blotting technique, was immobilized on the protein G layer. The formation of the SAM, the protein G layer and the sequential binding of the antibody against V. cholera O1 were investigated with SPR spectroscopy. As the number of fabricated layers increased, the minimum angle of plasmon resonance was increased accordingly. The target bacteria, V. cholera O1, was measured with the fabricated immunosensor, whose detection range was between 10(5) and 10(9) cells/mL.

Protein microarrays: a chance to study microorganisms?

Within the last 5 years, protein microarrays have been developed and applied to multiple approaches: identification of protein-protein interactions or protein-small molecule interactions, cancer profiling, detection of microorganisms and toxins, and identification of antibodies due to allergens, autoantigens, and pathogens. Protein microarrays are small size (typically in the microscopy slide format) planar analytical devices with probes arranged in high density to provide the ability to screen several hundred to thousand known substrates (e.g., proteins, peptides, antibodies) simultaneously. Due to their small size, only minute amounts of spotted probes and analytes (e.g., serum) are needed; this is a particularly important feature, for these are limited or expensive. In this review, different types of protein microarrays are reviewed: protein microarrays (PMAs), with spotted proteins or peptides; antibody microarrays (AMAs), with spotted antibodies or antibody fragments (e.g., scFv); reverse phase protein microarrays (RPMAs), a special form of PMA where crude protein mixtures (e.g., cell lysates, fractions) are spotted; and nonprotein microarrays (NPMAs) where macromolecules other than proteins and nucleic acids (e.g., carbohydrates, monosaccharides, lipopolysaccharides) are spotted. In this study, exemplary experiments for all types of protein arrays are discussed wherever applicable with regard to investigations of microorganisms.