Detection of norovirus capsid proteins in faecal and food samples by a real time immuno-PCR method

Improving the Detection and Understanding of Infectious Human Norovirus in Food and Water Matrices: A Review of Methods and Emerging Models

Human norovirus (HuNoV) is a leading global cause of viral gastroenteritis, contributing to numerous outbreaks and illnesses annually. However, conventional cell culture systems cannot support the cultivation of infectious HuNoV, making its detection and study in food and water matrices particularly challenging. Recent advancements in HuNoV research, including the emergence of models such as human intestinal enteroids (HIEs) and zebrafish larvae/embryo, have significantly enhanced our understanding of HuNoV pathogenesis. This review provides an overview of current methods employed for HuNoV detection in food and water, along with their associated limitations. Furthermore, it explores the potential applications of the HIE and zebrafish larvae/embryo models in detecting infectious HuNoV within food and water matrices. Finally, this review also highlights the need for further optimization and exploration of these models and detection methods to improve our understanding of HuNoV and its presence in different matrices, ultimately contributing to improved intervention strategies and public health outcomes.

Electrochemical peptide nucleic acid functionalized α-Fe2O3/Fe3O4 nanosheets for detection of CYP2C19*2 gene

The CYP2C19*2 gene carriers and non-carriers are closely related to the dosage of clopidogrel. To correctly guide the use of clopidogrel and promote individualized therapy, an ultra-sensitive electrochemical biosensor was developed for the detection of CYP2C19*2 gene. The heterogeneous α-Fe₂O₃/Fe₃O₄ nanosheets were prepared via the hydrothermal-calcination process, and the preparation parameters were optimized. The average diameter and thickness of the nanosheets were approximately 150 nm and 53 nm, respectively; and the saturation magnetization was 80.2 emu/g. The α-Fe₂O₃/Fe₃O₄@Au nanosheets were prepared by sodium borohydride reduction method, and self-assembled to the electrode surface with magnetic field. Ultra-sensitive detection of CYP2C19*2 gene was realized through the recognition ability of strong single base mismatching of peptide nucleic acid and signal amplification effect of magnetic α-Fe₂O₃/Fe₃O₄@Au nanosheets. Under optimal detection conditions, the current had a good linear correlation with the negative logarithm of CYP2C19*2 gene concentration in the range 1 pM-1 nM, and the detection limit was 0.64 pM (S/N = 3). Meanwhile, the electrochemical signals of target DNA and incomplete complementary DNA were detected. The constructed biosensor exhibited good selectivity, reproducibility, and stability, providing a promising strategy for the detection of other gene mutations by electrochemical biosensors.

Immuno-PCR technology for detection of natural human antibodies against Lec disaccharide

The development of an immuno-PCR assay for quantitation of low amounts of anti-glycan human antibodies is described. The sensitivity of the assay for determination of low-affinity anti-Le^C IgM has been found to be 4 ng/ml (~100 pg per sample), thus being two orders of magnitude higher compared to the conventional ELISA with the same antigen.

Highly sensitive ligand-binding assays in pre-clinical and clinical applications: immuno-PCR and other emerging techniques

Recombinant DNA technology and corresponding innovations in molecular biology, chemistry and medicine have led to novel therapeutic biomacromolecules as lead candidates in the pharmaceutical drug development pipelines. While monoclonal antibodies and other proteins provide therapeutic potential beyond the possibilities of small molecule drugs, the concomitant demand for supportive bioanalytical sample testing creates multiple novel challenges. For example, intact macromolecules can usually not be quantified by mass-spectrometry without enzymatic digestion and isotopically labeled internal standards are costly and/or difficult to prepare. Classical ELISA-type immunoassays, on the other hand, often lack the sensitivity required to obtain pharmacokinetics of low dosed drugs or pharmacodynamics of suitable biomarkers. Here we summarize emerging state-of-the-art ligand-binding assay technologies for pharmaceutical sample testing, which reveal enhanced analytical sensitivity over classical ELISA formats. We focus on immuno-PCR, which combines antibody specificity with the extremely sensitive detection of a tethered DNA marker by quantitative PCR, and alternative nucleic acid-based technologies as well as methods based on electrochemiluminescence or single-molecule counting. Using case studies, we discuss advantages and drawbacks of these methods for preclinical and clinical sample testing.

Development of a real-time immuno-PCR assay for the quantification of 17β-estradiol in water

A competitive real-time (RT) immuno-polymerase chain reaction (iPCR) (RT-iPCR) assay was developed for the sensitive quantification of 17β-estradiol in water. Using a universal iPCR method and polyclonal antibodies, 17β-estradiol was accurately quantified at concentrations ranging from 1 pg mL(-1) to 10 µg mL(-1). The RT-iPCR assay's limit of detection was 0.7 pg mL(-1). The RT-iPCR assay provided an 800-fold increase in sensitivity as well as an expanded working range compared with the corresponding enzyme-linked immunosorbent assay. Assay cross-reactivity to estrone and estriol, two structurally related estrogens, was below 8%. Water samples spiked with 17β-estradiol were analyzed by RT-iPCR to determine the assay's potential as a rapid screen for the monitoring of manure-borne estrogens in the environment. The assay showed recoveries of 82, 102 and 103% for Milli-Q, tap, and irrigation water, respectively, without requiring sample extraction or concentration prior to analysis.

Detection of small amounts of human adenoviruses in stools: comparison of a new immuno real-time PCR assay with classical tools

The detection of low virus concentrations in biological matrices, especially stool samples, is facing significant limitations as far as common diagnostic methods (enzyme-linked-immunosorbent assay (ELISA) or quantitative real-time PCR (qPCR)) are considered. Here the development of a new immuno real-time PCR (iPCR) is described and its performance in the detection of human adenoviruses (HAdVs) in spiked stools is compared with those of ELISA and qPCR assays. For the iPCR, detection of the sandwich formed by the complexation of capture antibody-antigen-detection antibody was performed by qPCR thanks to the substitution of peroxydase by a chimeric DNA. This modification increased the detection sensitivity 200-fold compared to ELISA. The direct qPCR results revealed that only 0.3–9.5% of the spiked HAdV were detectable, resulting from important losses of DNA occurring at the extraction step. This step was not necessary in the iPCR workflow, avoiding this drawback. The losses of viral particles occurred at the elution step from the stool only. The recovery rate of the iPCR was thus better and ranged between 21 and 54%. As a result, iPCR enabled the detection of lower virus concentrations in stool samples compared to those detected by ELISA and qPCR. The iPCR could be considered as a ‘hyper sensitive ELISA’ for early detection of HAdV infections, especially in the case of immunocompromised patients after haematopoietic stem cell transplant.

Detection of potential microbial antigens by immuno-PCR (PCR-amplified immunoassay)

Immuno-PCR (PCR-amplified immunoassay; I-PCR) is a novel ultrasensitive method combining the versatility of ELISA with the sensitivity of nucleic acid amplification of PCR. The enormous exponential amplification power of PCR in an I-PCR assay leads to at least a 10(2)-10(4)-fold increase in sensitivity compared with an analogous ELISA. I-PCR has been used to detect many biological molecules such as proto-oncogenes, toxins, cytokines, hormones, and biomarkers for autoimmune and Alzheimer's diseases, as well as microbial antigens and antibodies, and it can be adapted as a novel diagnostic tool for various infectious and non-infectious diseases. Quantitative real-time I-PCR has the potential to become the most analytically sensitive method for the detection of proteins. The sensitivity and specificity of a real-time I-PCR assay can be enhanced further with the use of magnetic beads and nanoparticles. This review is primarily focused on the detection of potential viral, bacterial and parasitic antigens by I-PCR assay, thus enabling their application for immunological research and for early diagnosis of infectious diseases.

Investigating norovirus removal by microfiltration, ultrafiltration, and precoagulation-microfiltration processes using recombinant norovirus virus-like particles and real-time immuno-PCR

The removal of microorganisms by drinking water treatment processes has been widely investigated in laboratory-scale experiments using artificially propagated microorganisms. However, this approach cannot be applied to norovirus removal, because this virus does not grow in cell or organ culture, and this fact has hampered our ability to investigate its behavior during drinking water treatment. To overcome this difficulty, our research group previously used recombinant norovirus virus-like particles (rNV-VLPs), which consist of an artificially expressed norovirus capsid protein, in laboratory-scale drinking water treatment experiments. However, the enzyme-linked immunosorbent assay (ELISA) method generally used to detect rNV-VLPs is not sensitive enough to evaluate high removal ratios such as those obtained by ultrafiltration (UF). We therefore developed and applied a real-time immuno-polymerase chain reaction (iPCR) assay for rNV-VLP quantification to investigate norovirus removal by microfiltration (MF), UF, and hybrid precoagulation-MF processes. The rNV-VLP detection limit with the developed iPCR assay was improved at least 1000-fold compared with ELISA. Whereas MF with a nominal pore size of 0.1 μm could not eliminate NV-VLPs, a 4-log reduction was achieved by UF with a molecular weight cutoff of 1 kDa. When MF was combined with precoagulation (≥10 μmol-Fe/L for ferric chloride; ≥20 μmol-Al/L for polyaluminum chloride; ≥40 μmol-Al/L for alum), the performance of the hybrid process in eliminating rNV-VLPs was greater than that achieved by the 1 kDa UF. For all processes, the removal ratios of the bacteriophages MS2 and Qβ were greater than the rNV-VLP removal ratios by 1-2 logs, so neither bacteriophage can be recommended as a possible conservative surrogate for predicting the behavior of native NV during these processes.

Immuno-polymerase chain reaction as a unique molecular tool for detection of infectious agents

Theoretically, the immuno-polymerase chain reaction (IPCR) method is the most sensitive technique for the detection of proteins and gains its uniqueness through the exponential amplification of a signal-generating nucleic acid intermediate attached to a protein target. This method is similar to PCR for the detection of nucleic acid targets, and has now been shown to offer the ability to detect infectious agents where nucleic acids are not present. Although the technical development of IPCR has taken a torturous path down a winding avenue of encouraging advances, the method remains rarely utilized by the scientific community and completely unused as a clinical diagnostic test approved by a national accrediting agency. Although the use of real-time instrumentation has enhanced the performance of IPCR to higher levels of statistical accuracy and reproducibility, as compared with the conventional method, its application remains limited by the high standards required for clinical diagnoses of infectious diseases. This review summarizes experimental data published to date describing the utilization of the IPCR method as it relates to the detection and diagnosis of human infectious disease, and examines the progressive development of this method, as well as the factors impeding its universal application as a clinical diagnostic tool. With further standardization and validation, the IPCR method has the potential to become the most analytically sensitive method available for the detection of target proteins of infectious diseases.

Enhanced detection of host response antibodies to Borrelia burgdorferi using immuno-PCR

Lyme disease is the fastest-growing zoonotic disease in North America. Current methods for detection of Borrelia burgdorferi infection are challenged by analysis subjectivity and standardization of antigen source. In the present study, we developed an immuno-PCR (iPCR)-based approach employing recombinant in vivo-expressed B. burgdorferi antigens for objective detection of a host immune response to B. burgdorferi infection. iPCR is a liquid-phase protein detection method that combines the sensitivity of PCR with the specificity and versatility of immunoassay-based protocols. Use of magnetic beads coated with intact spirochetes provided effective antigen presentation and allowed detection of host-generated antibodies in experimentally infected mice at day 11 postinoculation, whereas host-generated antibodies were detected at day 14 by enzyme-linked immunosorbent assay (ELISA) and day 21 by immunoblotting. Furthermore, magnetic beads coated with recombinant B. burgdorferi in vivo-expressed antigen OspC or BmpA demonstrated positive detection of host-generated antibodies in mice at day 7 postinoculation with markedly increased iPCR signals above the background, with the quantification cycle (C(q)) value for each sample minus the mean background C(q) plus 3 standard deviations (ΔC(q)) being 4 to 10, whereas ΔC(q) was 2.5 for intact spirochete-coated beads. iPCR demonstrated a strong correlation (Spearman rank correlation = 0.895, P < 0.0001) with a commercial ELISA for detection of host antibodies in human Lyme disease patient sera using the B. burgdorferi VlsE C6 peptide. In addition, iPCR showed potential applicability for direct detection of spirochetes in blood. The results presented here indicate that our iPCR assay has the potential to provide an objective format that can be used for sensitive detection of multiple host response antibodies and isotypes to B. burgdorferi infection.

Nanobiotechnologies for the detection and reduction of pathogens

Advances in the manipulation of nanomaterials has permitted the development of nanobiotechnology with enhanced sensitivities and improved response times. Low levels of infection of the major pathogens require the need for sensitive detection platforms and the properties of nanomaterials make them suitable for the development of assays with enhanced sensitivity, improved response time and increased portability. Nanobiotechnologies focusing on the key requirements of signal amplification and pre-concentration for the development of sensitive assays for food-borne pathogen detection in food matrices will be described and evaluated. The potential that exists for the use of nanomaterials as antimicrobial agents will also be examined.

Viral contaminants of molluscan shellfish: detection and characterisation

Environmental virology started with the detection of poliovirus in water. Since then other enteric viruses responsible for gastroenteritis and hepatitis have replaced enteroviruses as the main target for detection. Most shellfish-borne viral outbreaks are restricted to norovirus and hepatitis A virus, making them the main targets for bivalve virological analysis. The inclusion of virus analysis in regulatory standards for viruses in molluscan bivalve samples must overcome several shortcomings such as the technical difficulties and high costs of virus monitoring, the lack of harmonised and standardised assays and the challenge posed by the ever-changing nature of viruses. Nowadays methods are available to detect, quantify and characterise viral pathogens in molluscan shellfish to reduce the risks of shellfish-borne virus diseases.

Two-log increase in sensitivity for detection of norovirus in complex samples by concentration with porcine gastric mucin conjugated to magnetic beads

Human histo-blood group antigens (HBGA) have been identified previously as candidate receptors for human norovirus (NOR). Type A, type H1, and Lewis HBGA in humans have been identified as major HBGA for NOR binding. We have found that pig stomach (gastric) mucin (PGM) contains blood group A, H1, and Lewis b HBGA and binds to multiple strains of NOR more broadly than do specific antibodies to NOR. Both genogroup I (GGI) and GGII NOR strains were recovered by PGM-conjugated magnetic beads. A fecal sample containing GGII NOR was detected at a dilution of 1:1,000,000 by the standard RNA extraction procedure, whereas NOR in a 1:100,000,000 dilution could be concentrated by PGM-conjugated magnetic beads and NOR in spiked food samples (e.g., oyster extract, strawberry, raspberry, and lettuce) was captured by PGM, thus minimizing the reverse transcription-PCR inhibitors in food and increasing sensitivity.

Sensitivity by combination: immuno-PCR and related technologies

The versatility of immunoassays for the detection of antigens can be combined with the signal amplification power of nucleic acid amplification techniques in a broad range of innovative detection strategies. This review summarizes the spectrum of both, DNA-modification techniques used for assay enhancement and the resulting key applications. In particular, it focuses on the highly sensitive immuno-PCR (IPCR) method. This technique is based on chimeric conjugates of specific antibodies and nucleic acid molecules, the latter of which are used as markers to be amplified by PCR or related techniques for signal generation and read-out. Various strategies for the combination of antigen detection and nucleic acid amplification are discussed with regard to their laboratory analytic performance, including novel approaches to the conjugation of antibodies with DNA, and alternative pathways for signal amplification and detection. A critical assessment of advantages and drawbacks of these methods for a number of applications in clinical diagnostics and research is conducted. The examples include the detection of viral and bacterial antigens, tumor markers, toxins, pathogens, cytokines and other targets in different biological sample materials.

Ultrasensitive assays for proteins

Proteins are essential components of organisms and are involved in a wide range of biological functions. There are increasing demands for ultra-sensitive protein detection, because many important protein biomarkers are present at ultra-low levels, especially during the early stages of disease. Measuring proteins at low levels is also crucial for investigations of the protein synthesis and functions in biological systems. In this review, we summarize the recent developments of novel technology enabling ultrasensitive protein detection. We focus on two groups of techniques that involve either polymerase amplification of affinity DNA probes or signal amplification by the use of nano-/micro-materials. The polymerase-based amplification of affinity DNA probes indirectly improves the sensitivity of protein detection by increasing the number of detection molecules. The use of nano-/micro-materials conjugated to affinity probes enhances the measurement signals by using the unique electrical, optical, and catalytic properties of these novel materials. This review describes the basic principles, performances, applications, merits, and limitations of these techniques.

Procedure for rapid concentration and detection of enteric viruses from berries and vegetables

Several hepatitis A virus (HAV) and norovirus (NV) outbreaks due to consumption of berries and vegetables have been reported during recent years. To facilitate the detection of enteric viruses that may be present on different fresh and frozen products, we developed a rapid and sensitive detection method for HAV, NV, and rotavirus (RV). Initial experiments focused on optimizing the composition of the elution buffer, improving the viral concentration method, and evaluating the performance of various extraction kits. Viruses were extracted from the food surface by a direct elution method in a glycine-Tris (pH 9.5) buffer containing 1% beef extract and concentrated by ultrafiltration. Occasionally, PCR inhibitors were present in the processed berry samples, which gave relatively poor detection limits. However, this problem was overcome by adding a pectinase treatment in the protocol, which markedly improved the sensitivity of the method. After optimization, this concentration method was applied in combination with real-time reverse transcription-PCR (RT-PCR) using specific primers in various types of berries and vegetables. The average detection limits were 1 50% tissue culture infective dose (TCID(50)), 54 RT-PCR units, and 0.02 TCID(50) per 15 g of food for HAV, NV, and RV, respectively. Based on our results, it is concluded that this procedure is suitable to detect and quantify enteric viruses within 6 h and can be applied for surveillance of enteric viruses in fresh and frozen products.