SYTO dyes and EvaGreen outperform SYBR Green in real-time PCR

Real-time fluorescence loop-mediated isothermal amplification assays for detection of zoonotic malaria Plasmodium parasites

BACKGROUND

Natural human infections by Plasmodium cynomolgi and P. inui have been reported recently and gain the substantial attention from Southeast Asian countries. Zoonotic transmission of non-human malaria parasites to humans from macaque monkeys occurred through the bites of the infected mosquitoes. The objective of this study is to establish real-time fluorescence loop-mediated isothermal amplification (LAMP) assays for the detection of zoonotic malaria parasites by combining real-time fluorescent technology with the isothermal amplification technique.

METHODS

By using 18S rRNA as the target gene, the primers for P. cynomolgi, P. coatneyi and P. inui were newly designed in the present study. Four novel real-time fluorescence LAMP assays were developed for the detection of P. cynomolgi, P. coatneyi, P. inui and P. knowlesi. The entire amplification process was completed in 60 min, with the assays performed at 65 °C. By using SYTO-9 as the nucleic acid intercalating dye, the reaction was monitored via real-time fluorescence signal.

RESULTS

There was no observed cross-reactivity among the primers from different species. All 70 field-collected monkey samples were successfully amplified by real-time fluorescence LAMP assays. The detection limit for P. cynomolgi, P. coatneyi and P. knowlesi was 5 × 109 copies/µL. Meanwhile, the detection limit of P. inui was 5 × 1010 copies/µL.

CONCLUSION

This is the first report of the detection of four zoonotic malaria parasites by real-time fluorescence LAMP approaches. It is an effective, rapid and simple-to-use technique. This presented platform exhibits considerable potential as an alternative detection for zoonotic malaria parasites.

Evaluation of A Simple DNA Extraction Method and Its Combination with Loop-Mediated Isothermal Amplification Assays for Rapid Plasmodium knowlesi Diagnosis

The initial and vital stage in the diagnosis of malaria involves extracting DNA. The efficiency of malaria testing is restricted by the multiple steps involved in commercial DNA extraction kits. We attempted to improve an existing loop-mediated isothermal amplification (LAMP) for the detection of Plasmodium knowlesi by using a simple DNA extraction approach, making it a feasible option for mass screening. We utilized a simple nucleic acid extraction method directly from whole blood for the detection of P. knowlesi, taking only 5 min to complete. The extracted DNA was evaluated by two fluorescent-based LAMP and one colorimetric-based LAMP assay. The detection limit for both SYTO-LAMP and SYBR green-LAMP was 0.00001% and 0.0001% parasitemia, respectively. Meanwhile, neutral red-LAMP had a detection limit of 0.01% parasitemia. Combining this simple and inexpensive DNA extraction method, SYTO-LAMP could serve as an alternative molecular diagnosis for the detection of P. knowlesi and other human Plasmodium spp.

Binding, brightness, or noise? Extracting temperature-dependent properties of dye bound to DNA

We present a method for extracting temperature-dependent thermodynamic and photophysical properties of SYTO-13 dye bound to DNA from fluorescence measurements. Together, mathematical modeling, control experiments, and numerical optimization enable dye binding strength, dye brightness, and experimental noise (or error) to be discriminated from one another. By focusing on the low-dye-coverage regime, the model avoids bias and can simplify quantification. Utilizing the temperature-cycling capabilities and multi-reaction chambers of a real-time PCR machine increases throughput. Significant well-to-well and plate-to-plate variation is quantified by using total least squares to account for error in both fluorescence and nominal dye concentration. Properties computed independently for single-stranded DNA and double-stranded DNA by numerical optimization are consistent with intuition and explain the advantageous performance of SYTO-13 in high-resolution melting and real-time PCR assays. Distinguishing between binding, brightness, and noise also clarifies the mechanism for the increased fluorescence of dye in a solution of double-stranded DNA compared to single-stranded DNA; in fact, the explanation changes with temperature.

Identification of extremely GC-rich micro RNAs for RT-qPCR data normalization in human plasma

We aimed at extending the repertoire of high-quality miRNA normalizers for reverse transcription-quantitative PCR (RT-qPCR) of human plasma with special emphasis on the extremely guanine-cytosine-rich portion of the miRNome. For high-throughput selection of stable candidates, microarray technology was preferred over small-RNA sequencing (sRNA-seq) since the latter underrepresented miRNAs with a guanine-cytosine (GC) content of at least 75% (p = 0.0002, n = 2). miRNA abundances measured on the microarray were ranked for consistency and uniformity using nine normalization approaches. The eleven most stable sequences included miRNAs of moderate, but also extreme GC content (45%-65%: miR-320d, miR-425-5p, miR-185-5p, miR-486-5p; 80%-95%: miR-1915-3p, miR-3656-5p, miR-3665-5p, miR-3960-5p, miR-4488-5p, miR-4497 and miR-4787-5p). In contrast, the seven extremely GC-rich miRNAs were not found in the two plasma miRNomes screened by sRNA-seq. Stem-loop RT-qPCR was employed for stability verification in 32 plasma samples of healthy male Caucasians (age range: 18-55 years). In general, inter-individual variance of miRNA abundance was low or very low as indicated by coefficient of variation (CV) values of 0.6%-8.2%. miR-3665 and miR-1915-3p outperformed in this analysis (CVs: 0.6 and 2.4%, respectively). The eight most stable sequences included four extremely GC-rich miRNAs (miR-1915-3p, miR-3665, miR-4787-5p and miR-4497). The best-performing duo normalization factor (NF) for the condition of human plasma, miR-320d and miR-4787-5p, also included a GC-extreme miRNA. In summary, the identification of extremely guanine-cytosine-rich plasma normalizers will help to increase accuracy of PCR-based miRNA quantification, thus raise the potential that miRNAs become markers for psychological stress reactions or early and precise diagnosis of clinical phenotypes. The novel miRNAs might also be useful for orthologous contexts considering their conservation in related animal genomes.

Two Leishmania species separation targeting the ITS-rDNA and Cyt b genes by developing and evaluating HRM- qPCR

BACKGROUND

Incidence of Cutaneous Leishmaniasis as an infectious and neglected disease is increasing, for the diagnosis of which several traditional methods and conventional PCR techniques have been developed, employing different genes for species identification.

METHODS

Leishmania parasites were sampled, DNA was extracted, and new specific and sensitive primers were designed. Two ITS-rDNA and Cyt b genes were targeted by qPCR using the High- Resolution Melting method to identify Leishmania parasites. The standard curves were drawn, compared, and identified by high-resolution melting curve analysis.

RESULTS

Melting temperature and Cycle of Threshold of ITS-rDNA was higher than Cyt b but Cyt b was more sensitive than ITS-rDNA when Leishmania major and Leishmania tropica were analyzed and evaluated. By aligning melt curves, normalizing fluorescence curves, and difference plotting melt curves, each Leishmania species was distinguished easily. L. major and L. tropica were separated at 83.6 °C and 84.7 °C, respectively, with less than 0.9 °C of temperature difference. Developing sensitivity and specificity of real-time PCR based on EvaGreen could detect DNA concentration to less than one pmol.

CONCLUSIONS

Precise identification of Leishmania parasites is crucial for strategies of disease control. Real-time PCR using EvaGreen provides rapid, highly sensitive, and specific detection of parasite's DNA. The modified High-Resolution Melting could determine unique curves and was able to detect single nucleotide polymorphisms according to small differences in the nucleotide content of Leishmania parasites.

Recent Advances in Digital Biosensing Technology

Digital biosensing assays demonstrate remarkable advantages over conventional biosensing systems because of their ability to achieve single-molecule detection and absolute quantification. Unlike traditional low-abundance biomarking screening, digital-based biosensing systems reduce sample volumes significantly to the fL-nL level, which vastly reduces overall reagent consumption, improves reaction time and throughput, and enables high sensitivity and single target detection. This review presents the current technology for compartmentalizing reactions and their applications in detecting proteins and nucleic acids. We also analyze existing challenges and future opportunities associated with digital biosensing and research opportunities for developing integrated digital biosensing systems.

Development of Droplet Digital PCR Assay for Detection of Seed-Borne Burkholderia glumae and B. gladioli Causing Bacterial Panicle Blight Disease of Rice

Bacterial panicle blight of rice or bacterial grain rot of rice is a worldwide rice disease. Burkholderia glumae and B. gladioli are the causal agents. The early and accurate detection of seed-borne B. glumae and B. gladioli is critical for domestic and international quarantine and effective control of the disease. Here, genomic analyses revealed that B. gladioli contains five phylogroups and the BG1 primer pair designed to target the 3’-end sequence of a gene encoding a Rhs family protein is specific to B. glumae and two phylogroups within B. gladioli. Using the BG1 primer pair, a 138-bp DNA fragment was amplified only from the tested panicle blight pathogens B. glumae and B. gladioli. An EvaGreen droplet digital PCR (dPCR) assay on detection and quantification of the two pathogens was developed from a SYBR Green real-time quantitative PCR (qPCR). The detection limits of the EvaGreen droplet dPCR on the two pathogens were identical at 2 × 10³ colony forming units (CFU)∙mL⁻¹ from bacterial suspensions and 2 × 10² CFU∙seed⁻¹ from rice seeds. The EvaGreen droplet dPCR assay showed 10-fold detection sensitivity of the SYBR Green qPCR and could detect a single copy of the target gene in a 20-μL assay. Together, the SYBR Green qPCR assay allows for routine high-throughput detection of the panicle blight pathogens and the EvaGreen droplet dPCR assay provides a high-sensitive and high-accurate diagnostic method for quarantine of the pathogens.

Toward a next-generation diagnostic tool: A review on emerging isothermal nucleic acid amplification techniques for the detection of SARS-CoV-2 and other infectious viruses

As the COVID-19 pandemic continues to affect human health across the globe rapid, simple, point-of-care (POC) diagnosis of infectious viruses such as SARS-CoV-2 remains challenging. Polymerase chain reaction (PCR)-based diagnosis has risen to meet these demands and despite its high-throughput and accuracy, it has failed to gain traction in the rapid, low-cost, point-of-test settings. In contrast, different emerging isothermal amplification-based detection methods show promise in the rapid point-of-test market. In this comprehensive study of the literature, several promising isothermal amplification methods for the detection of SARS-CoV-2 are critically reviewed that can also be applied to other infectious viruses detection. Starting with a brief discussion on the SARS-CoV-2 structure, its genomic features, and the epidemiology of the current pandemic, this review focuses on different emerging isothermal methods and their advancement. The potential of isothermal amplification combined with the revolutionary CRISPR/Cas system for a more powerful detection tool is also critically reviewed. Additionally, the commercial success of several isothermal methods in the pandemic are highlighted. Different variants of SARS-CoV-2 and their implication on isothermal amplifications are also discussed. Furthermore, three most crucial aspects in achieving a simple, fast, and multiplexable platform are addressed.

Development of a high resolution melting method based on a novel molecular target for discrimination between Bacillus cereus and Bacillus thuringiensis

Delimitation within the Bacillus cereus group is confusing due to the highly similar genetic background of its constituent bacteria. This study aimed to develop a rapid and efficient method for the identification of Bacillus cereus and Bacillus thuringiensis, two closely related species within the B. cereus group. Using average nucleotide identity analysis (ANI) and ribosomal multilocus sequence typing (rMLST), the authenticity of the genomes of B. cereus and B. thuringiensis was determined. Emetic B. cereus and Bacillus bombysepticus were also included to provide novel genomic insights into the boundaries within the B. cereus group. Using pan-genome analysis, ispD, a novel core and single-copy molecular target, was identified for the differentiation between B. cereus and B. thuringiensis. Based on the single nucleotide polymorphism within ispD, a high resolution melting (HRM) method for the determination of B. cereus and B. thuringiensis was developed. This method can not only distinguish B. cereus and B. thuringiensis, but can also separate B. cereus from other foodborne pathogenic bacteria. The detection limit of this method could reach 1 pg of pure genomic DNA and 3.7 × 10² cfu/mL of pure culture. Moreover, this new method could effectively differentiate B. cereus and B. thuringiensis in spiked, mixed, and real food samples. Collectively, the established HRM method can provide a new reference paradigm for the sensitive and specific nucleic acid detection of pathogens with identical genomes.

A cost-effective and efficient approach for generating and assembling reagents for conducting real-time PCR

Real-time PCR is a widely used technique for quantification of gene expression. However, commercially available kits for real-time PCR are very expensive. The ongoing coronavirus pandemic has severely hampered the economy in a number of developing countries, resulting in a reduction in available research funding. The fallout of this will result in limiting educational institutes and small enterprises from using cutting edge biological techniques such as real-time PCR. Here, we report a cost-effective approach for preparing and assembling cDNA synthesis and real-time PCR mastermixes with similar efficiencies as commercially available kits. Our results thus demonstrate an alternative to commercially available kits.

Homebrew reagents for low-cost RT-LAMP

Reverse transcription-loop-mediated isothermal amplification (RT-LAMP) has gained popularity for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The high specificity, sensitivity, simple protocols, and potential to deliver results without the use of expensive equipment has made it an attractive alternative to RT-PCR. However, the high cost per reaction, the centralized manufacturing of required reagents, and their distribution under cold chain shipping limit RT-LAMP's applicability in low-income settings. The preparation of assays using homebrew enzymes and buffers has emerged worldwide as a response to these limitations and potential shortages. Here, we describe the production of Moloney murine leukemia virus reverse transcriptase and BstLF DNA polymerase for the local implementation of RT-LAMP reactions at low cost. These reagents compared favorably to commercial kits, and optimum concentrations were defined in order to reduce time to threshold, increase ON/OFF range, and minimize enzyme quantities per reaction. As a validation, we tested the performance of these reagents in the detection of SARS-CoV-2 from RNA extracted from clinical nasopharyngeal samples, obtaining high agreement between RT-LAMP and RT-PCR clinical results. The in-house preparation of these reactions results in an order of magnitude reduction in costs; thus, we provide protocols and DNA to enable the replication of these tests at other locations. These results contribute to the global effort of developing open and low-cost diagnostics that enable technological autonomy and distributed capacities in viral surveillance.

Toxoplasma gondii in mollusks and cold-blooded animals: a systematic review

Toxoplasma gondii (T. gondii) is known for its ability to infect warm-blooded vertebrates. Although T. gondii does not appear to parasitize cold-blooded animals, the occurrence of T. gondii infection in marine mammals raises concerns that cold-blooded animals (frogs, toad, turtles, crocodiles, snakes, and fish) and shellfish are potential sources of T. gondii. Therefore, this systematic review aimed to determine the prevalence of T. gondii in mollusks and cold-blooded animals worldwide. We searched PubMed, ScienceDirect, ProQuest, Scopus, and Web of Science from inception to 1 August 2020 for eligible papers in the English language and identified 26 articles that reported the prevalence of T. gondii in mollusks and cold-blooded animals. These articles were subsequently reviewed and data extracted using a standard form. In total, 26 studies [involving 9 cross-sectional studies including 2988 samples of cold-blooded animals (129 positive cases for T. gondii) and 18 cross-sectional studies entailing 13 447 samples of shellfish (692 positive cases for T. gondii)] were included in this study. Although this study showed that shellfish and cold-blooded animals could be potential sources of T. gondii for humans and other hosts that feed on them, further investigations are recommended to determine the prevalence of T. gondii in shellfish and cold-blooded animals.

High-throughput methods for measuring DNA thermodynamics

Understanding the thermodynamics of DNA motifs is important for prediction and design of probes and primers, but melt curve analyses are low-throughput and produce inaccurate results for motifs such as bulges and mismatches. Here, we developed a new, accurate and high-throughput method for measuring DNA motif thermodynamics called TEEM (Toehold Exchange Energy Measurement). It is a refined framework of comparing two toehold exchange reactions, which are competitive strand displacement between oligonucleotides. In a single experiment, TEEM can measure over 1000 ΔG° values with standard error of roughly 0.05 kcal/mol.

A quantitative loop-mediated isothermal amplification assay for detecting a novel goose astrovirus

In November 2017, a severe infectious disease that devastated the major goose-producing regions in China was found to be caused by a novel goose astrovirus (N-AstV). The objective of this study was to develop a quantitative loop-mediated isothermal amplification (qLAMP) assay for the rapid diagnosis of N-AstV characterized with gout, hemorrhage, and swellings of the kidneys. A set of 4 specific primers, 2 inner and 2 outer primers, targeting the ORF1a gene of N-AstV were designed for the assay which could be completed within 60 min at 65°C in a water bath or on a real-time PCR instrument for quantitative analysis. The qLAMP assay showed a high sensitivity with a detection limit of 1 × 10¹ copies of the target DNA/μL. There were no cross-reactions with other viruses, and the reproducibility of the assay was confirmed in intrasensitivity and intersensitivity assay tests with variability ranging from 0.61 to 2.21%. The results indicated that the qLAMP assay for N-AstV was a simple, accurate, rapid, sensitive, and specific, especially useful for field detection.

A novel 5-Plex qPCR-HRM assay detecting human diarrheal parasites

Background

Intestinal parasitic diseases occur worldwide, and their diagnosis poses considerable challenges. Cryptosporidium spp., Entamoeba histolytica, Giardia intestinalis, (and, arguably, Dientamoeba fragilis and Blastocystis spp.) are among the most important and common parasitic protozoans causing diarrhea. Several multiplex real-time PCR assays have been developed for the synchronous detection of these parasites. However, most assays include the use of hydrolysis probes, increasing the cost of stool examination. In this study, we designed and evaluated a real-time PCR protocol, based on high-resolution melting (HRM) curve analysis, to simultaneously detect and differentiate five gastrointestinal parasites.

Results

Using a blinded panel of 143 clinical samples with laboratory diagnostic data to evaluate the method, we obtained a 95.8% concordance with conventional methods. Moreover, 4.2% of the samples were positive for D. fragilis and 2.8% additional Cryptosporidium infections were found with our multiplex assay. Our method is sensitive and specific for the selected parasites with the additional possibility of being run in single-plex as a backup control for mixed infections.

Conclusions

The assay is a convenient and cost-effective method that could contribute to a quicker and accurate diagnosis as well as to more targeted therapies of parasite-derived diarrhea. Finally, this new multiplex PCR assay could also be instrumental in epidemiology studies on these parasites.

PCR inhibition in qPCR, dPCR and MPS-mechanisms and solutions

DNA analysis has seen an incredible development in terms of instrumentation, assays and applications over the last years. Massively parallel sequencing (MPS) and digital PCR are now broadly applied in research and diagnostics, and quantitative PCR is used for more and more practises. All these techniques are based on in vitro DNA polymerization and fluorescence measurements. A major limitation for successful analysis is the various sample-related substances that interfere with the analysis, i.e. PCR inhibitors. PCR inhibition affects library preparation in MPS analysis and skews quantification in qPCR, and some inhibitors have been found to quench the fluorescence of the applied fluorophores. Here, we provide a deeper understanding of mechanisms of specific PCR inhibitors and how these impact specific analytical techniques. This background knowledge is necessary in order to take full advantage of modern DNA analysis techniques, specifically for analysis of samples with low amounts of template and high amounts of background material. The classical solution to handle PCR inhibition is to purify or dilute DNA extracts, which leads to DNA loss. Applying inhibitor-tolerant DNA polymerases, either single enzymes or blends, provides a more straightforward and powerful solution. This review includes mechanisms of specific PCR inhibitors as well as solutions to the inhibition problem in relation to cutting-edge DNA analysis.

Pneumocystis jirovecii colonization and its association with pulmonary diseases: a multicenter study based on a modified loop-mediated isothermal amplification assay

Background

Pneumocystis jirovecii (P. jirovecii) is an opportunistic fungal pathogen and the role of its colonization in pulmonary diseases has become a popular focus in recent years. The aim of this study was to develop a modified loop-mediated isothermal amplification (LAMP) assay for detection of Pneumocystis jirovecii (P. jirovecii) DNA amongst non-HIV patients with various pulmonary diseases and use it to examine the prevalence and assess the association of P. jirovecii colonization with clinical characteristics of these diseases.

Methods

We modified the previously reported LAMP assay for P. jirovecii by adding real-time detection. This method was used to detect P. jirovecii colonization in pulmonary samples collected from 403 non-HIV patients with various pulmonary diseases enrolled from 5 hospitals in China. We determined the prevalence of P. jirovecii colonization in 7 types of pulmonary diseases and assessed the association of P. jirovecii colonization with clinical characteristics of these diseases.

Results

The modified LAMP assay showed no cross-reactivity with other common pulmonary microbes and was 1000 times more sensitive than that of conventional PCR. Using the modified LAMP assay, we detected P. jirovecii colonization in 281 (69.7%) of the 403 patients enrolled. P. jirovecii colonization was more common in interstitial lung diseases than in chronic obstructive pulmonary disease (COPD) (84.6% vs 64.5%, P < 0.05). Patients with acute exacerbation of COPD had a higher prevalence of P. jirovecii colonization compared to patients with stabilized COPD (67.4% vs 43.3%, P < 0.05). P. jirovecii colonization was associated with decreased pulmonary function, increased levels of 1,3-β-D-glucan and C-reactive protein, and decreased levels of CD4+ T-cell counts (P < 0.05 for each). Approximately 70% of P. jirovecii colonized patients had confections with other fungi or bacteria.

Conclusions

We developed a modified LAMP assay for detecting P. jirovecii. Our multi-center study of 403 patients supports that P. jirovecii colonization is a risk factor for the development of pulmonary diseases and highlights the need to further study the pathogenesis and transmission of P. jirovecii colonization in pulmonary diseases.

Single-molecule analysis of nucleic acid biomarkers - A review

Nucleic acids are important biomarkers for disease detection, monitoring, and treatment. Advances in technologies for nucleic acid analysis have enabled discovery and clinical implementation of nucleic acid biomarkers. However, challenges remain with technologies for nucleic acid analysis, thereby limiting the use of nucleic acid biomarkers in certain contexts. Here, we review single-molecule technologies for nucleic acid analysis that can be used to overcome these challenges. We first discuss the various types of nucleic acid biomarkers important for clinical applications and conventional technologies for nucleic acid analysis. We then discuss technologies for single-molecule in vitro and in situ analysis of nucleic acid biomarkers. Finally, we discuss other ultra-sensitive techniques for nucleic acid biomarker detection.

Development of high-resolution melting curve analysis in rapid detection of vanA gene, Enterococcus faecalis, and Enterococcus faecium from clinical isolates

Background

High-resolution melting analysis (HRMA) is a novel molecular technique based on the real-time PCR that can be used to detect vancomycin resistance Enterococcus (VRE). The purpose of this study was to identify VRE species with HRMA in clinical isolates.

Results

Out of 49 Enterococcus isolates, 11 (22.44%) E. faecium isolates and 19 (38.77%) E. faecalis isolates were detected. Average melting temperatures for divIVA in E.faecalis, alanine racemase in E.faecium, and vanA in VRE strains were obtained as 79.9 ± 0.5 °C, 85.4 ± 0.5 °C, and 82.99 ± 0.5 °C, respectively. Furthermore, the data showed that the HRMA method was sensitive to detect 10⁰ CFU/ml for the divIVA, alanine racemase, and vanA genes. Also, out of 49 Enterococcus spp., which were isolated by HRMA assay, 8 isolates (16.32%) of E. faecium and 18 isolates (36.73%) of E. faecalis were detected. The vanA gene was reported in 2 isolates (25%) of E. faecium and 9 isolates (50%) of E. faecalis.

Conclusions

This study demonstrated that using the HRMA method, we can detect E. faecium, E. faecalis, and the vanA gene with high sensitivity and specificity.

Detection of extended-spectrum beta-lactamase cefotaxime resistance and virulence genes in Escherichia coli by duplex quantitative real-time PCR and melt curve analysis

Emerging virulent and antibiotic-resistant pathogens present a global public health risk. Routine monitoring of prevalence within the clinical, environmental and food production setting is vital. Quantitative real-time PCR (qPCR) coupled with melting curve analysis can rapidly and accurately characterize pathogens. We evaluated commercial qPCR mixes based on SYBR Green l and EvaGreen for developing an assay for simultaneously detecting antibiotic resistance (extended-spectrum beta-lactamase, ESBL and bla_CTX-M ) and virulence (stx1, stx2 and eae) genes in Escherichia coli (n = 12) isolated from irrigation water and irrigated vegetables. SYBR Green and EvaGreen detected two amplicons (stx1 and bla_CTX-M ) and (stx2 and eae) in a single reaction. A higher mean melting temperature (T_m ) separation between targeted amplicons and smoother melting curves were observed with the EvaGreen suggesting better performance when targeting multiple amplicons. Through simple stepwise optimization of DNA, cycling, primers, reaction volume and melting curve scanning rate, we adopted a conventional PCR assay for detection of large amplicons (375-1580 bp) for qPCR. This may facilitate development of cost-effective tailor-made assays for rapid and accurate monitoring of emerging foodborne and environmental pathogens in resource constrained regions.

Quantitative and rapid Plasmodium falciparum malaria diagnosis and artemisinin-resistance detection using a CMOS Lab-on-Chip platform

Early and accurate diagnosis of malaria and drug-resistance is essential to effective disease management. Available rapid malaria diagnostic tests present limitations in analytical sensitivity, drug-resistance testing and/or quantification. Conversely, diagnostic methods based on nucleic acid amplification stepped forwards owing to their high sensitivity, specificity and robustness. Nevertheless, these methods commonly rely on optical measurements and complex instrumentation which limit their applicability in resource-poor, point-of-care settings. This paper reports the specific, quantitative and fully-electronic detection of Plasmodium falciparum, the predominant malaria-causing parasite worldwide, using a Lab-on-Chip platform developed in-house. Furthermore, we demonstrate on-chip detection of C580Y, the most prevalent single-nucleotide polymorphism associated to artemisinin-resistant malaria. Real-time non-optical DNA sensing is facilitated using Ion-Sensitive Field-Effect Transistors, fabricated in unmodified complementary metal-oxide-semiconductor (CMOS) technology, coupled with loop-mediated isothermal amplification. This work holds significant potential for the development of a fully portable and quantitative malaria diagnostic that can be used as a rapid point-of-care test.

Development of an EvaGreen based real-time RT-PCR assay for rapid detection, quantitation and diagnosis of goose calicivirus

An unclassified calicivirus (CV) detected in geese was recently reported and proposed as a new member of the family Caliciviridae. There is limited information about the epidemiology, etiology and detection method of goose-origin CV (GCV) to date. In this study, an EvaGreen based fluorescence quantitative real-time RT-PCR assay was developed and optimized for the detection of GCVs. The assay sensitively detected GCV RNA template with a good linear standard curve. We also demonstrated the specificity and reproducibility of the detection method for GCVs. Thus, the method developed in this study will benefit the investigation of possible sporadic outbreaks of CV infections in geese, as well as epidemiological and etiological studies of GCVs.

Employing DNA binding dye to improve detection of Enterocytozoon hepatopenaei in real-time LAMP

Enterocytozoon hepatopenaei (EHP) is a pathogen in the pancreatic tissue of prawn, as reported in recent years. Enterosporidiosis caused by EHP in Penaeus genus is spreading widely, which seriously threatens the sustainable development of shrimp aquaculture in the world. Empolying the DNA binding dye of SYTO-16, a real-time quantitative loop-mediated isothermal amplification (LAMP) method has been established herein to detect EHP. The primer sequences used in the LAMP reaction were according to the SSU rRNA gene. The LAMP assay has reached a sensitivity of 10¹ copies/µL and no cross-reaction with other aquatic pathogens. Compared with normal PCR, the efficiency of the LAMP technique is more sensitive, which has a shorter detection time. The use of fluorescent nucleic acid dye (SYTO-16) reveals a more satisfactory performance relative to calcein. The quantitative LAMP assay can be considered as a valid tool for rapid detection of microsporidian in prawns. Our study provides a scientific basis to follow the effect of the pathogen infection on growth of cultured penaeid shrimp.

Development of an EvaGreen-based real-time PCR assay for detection of Aleutian mink disease virus

The objective of this study was to develop a rapid, sensitive and specific EvaGreen (EG)-based real-time PCR assay capable of detecting Aleutian mink disease virus (AMDV) and to evaluate the reliability of the assay for analysis of blood or tissue samples. For this assay, a pair of primers was designed based on a nonstructural protein (NS)-encoding gene of AMDV, and the identity of PCR products was identified based on a melting temperature of 82.8°C. The EG-based real-time PCR assay did not detect canine distemper virus or mink enteritis virus, and the assay could be used to detect Chinese and American AMDV strains, in contrast to a commercial TaqMan kit that could only detect American AMDV strains. The amplification efficiencies of the EG assay were 104.8% for the Chinese strain and 94.4% for the American strain, and the detection limit was 1 copy/μL of AMDV plasmid or 3 pg/μL of viral DNA (Chinese strain). The intra- and inter-assay variation coefficients of melting temperature were all lower than 0.15%, confirming the high reproducibility of the assay. Forty-five clinical blood samples were simultaneously analyzed using the EG real-time PCR, TaqMan kit and conventional PCR, and the detection rates were 91.1%, 0.0% and 86.7%, respectively. Serum samples were also collected from the corresponding blood samples and tested using the counterimmunoelectrophoresis (CIEP) assay, where positive samples accounted for 24.4% of the 45 samples. In conclusion, EG-based real-time PCR is a rapid, sensitive, universal assay that can be effectively utilized as a reliable and specific tool for detection and quantitation of AMDV.

Self-heating tilted fiber Bragg grating device for melt curve analysis of solid-phase DNA hybridization and thermal cycling

We demonstrate a DNA-based optical fiber device that uses an in-fiber grating, a light absorbing coating with surface anchored DNA, and a built-in optical thermometer. This device is used for precisely thermal cycling surface DNA spots bound by a simple UV cross-linking technique. Near-infrared light of wavelengths near 1550 nm and guided power near 300 mW is coupled out of the fiber core by a tilted fiber Bragg grating inscribed in the fiber and absorbed by the coating to increase its temperature to more than 95 °C. A co-propagating broadband light signal (also in the near-infrared region) is used to measure the reflection spectrum of the grating and thus the temperature from the wavelength shifts of the reflection peaks. The device is capable of sensitive DNA melt analysis and can be used for DNA amplification. Graphical abstract.

Extraction of Plant DNA by Microneedle Patch for Rapid Detection of Plant Diseases

In-field molecular diagnosis of plant diseases via nucleic acid amplification is currently limited by cumbersome protocols for extracting and isolating pathogenic DNA from plant tissues. To address this challenge, a rapid plant DNA extraction method was developed using a disposable polymeric microneedle (MN) patch. By applying MN patches on plant leaves, amplification-assay-ready DNA can be extracted within a minute from different plant species. MN-extracted DNA was used for direct polymerase chain reaction amplification of plant plastid DNA without purification. Furthermore, using this patch device, extraction of plant pathogen DNA ( Phytophthora infestans) from both laboratory-inoculated and field-infected leaf samples was performed for detection of late blight disease in tomato. MN extraction achieved 100% detection rate of late blight infections for samples after 3 days of inoculation when compared to the conventional gold standard cetyltrimethylammonium bromide (CTAB)-based DNA extraction method and 100% detection rate for all blind field samples tested. This simple, cell-lysis-free, and purification-free DNA extraction method could be a transformative approach to facilitate rapid sample preparation for molecular diagnosis of various plant diseases directly in the field.

Simultaneous detection of five pig viruses associated with enteric disease in pigs using EvaGreen real-time PCR combined with melting curve analysis

In recent years, a series of porcine diarrhea viruses such as porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), rotaviruses of group A (RVA), rotaviruses of group C (RVC), and porcine circovirus 2 (PCV2) caused enormous economic losses all over the world. While any of these viruses is capable to cause disease alone, there is often concurrent infection with more than one virus on pig farms. In this study, a multiplex real-time PCR method based on EvaGreen fluorescent dye and melting curve analysis was established to simultaneously detect these five viruses in a single closed tube. Five distinct melt peaks were obtained with different melting temperature (Tm) value corresponding to each of the five viruses. This method was highly sensitive to detect and distinguish TGEV, RVA, RVC, PEDV and PCV2 with the limits of detection ranging from 5 to 50 copies/μL. The intra-assay and inter-assay reproducibility were good with coefficient of variation of Tm and cycle threshold values less than 0.32% and 2.86%, respectively. Testing of 90 field samples by the single and multiplex real-time PCR assays demonstrated a concordance of 91.1%. Thus, the EvaGreen multiplex real-time PCR is a rapid, sensitive and low-cost diagnostic tool for differential detection and routine surveillance of TGEV, RVA, RVC, PEDV and PCV2 in pigs.

Optimised LAMP allows single copy detection of 35Sp and NOSt in transgenic maize using Bioluminescent Assay in Real Time (BART)

Loop-mediated amplification (LAMP) has been widely used to amplify and hence detect nucleic acid target sequences from various pathogens, viruses and genetic modifications. Two distinct types of primer are required for LAMP; hairpin-forming LAMP and displacement. High specificity arises from this use of multiple primers, but without optimal conditions for LAMP, sensitivity can be poor. We confirm here the importance of LAMP primer design, concentrations and ratios for efficient LAMP amplification. We further show that displacement primers are non-essential to the LAMP reaction at certain concentrations providing accelerating loop primers are present. We investigate various methods to quantify DNA extracts from GM maize certified reference materials to calculate the target copy numbers of template presented to the LAMP reaction, and show that LAMP can amplify transgenic promoter/terminator sequences in DNA extracted from various maize GM events using primers designed to target the 35S promoter (35Sp) or NOS terminator (NOSt) sequences, detection with both bioluminescence in real-time (BART) and fluorescent methods. With prior denaturation and HPLC grade LAMP primers single copy detection was achieved, showing that optimised LAMP conditions can be combined with BART for single copy targets, with simple and cost efficient light detection electronics over fluorescent alternatives.

Characterization of the binding interactions between EvaGreen dye and dsDNA

Understanding the dsDNA·EG binding interaction is important because the EvaGreen (EG) dye is increasingly used in real-time quantitative polymerase chain reaction, high resolution melting analysis, and routine quantification of DNA. In this work, a binding isotherm for the interactions of EG with duplex DNA (poly-dA₁₇·poly-dT₁₇) has been determined from the absorption and fluorescence spectra of the EG and dsDNA·EG complex. The isotherm has a sigmoidal shape and can be modeled with the Hill equation, indicating positive cooperativity for the binding interaction. A Scatchard plot of the binding data yields a concave-down curve in agreement with the Hill analysis of the binding isotherm for a positive cooperative binding interaction. Analysis of the Scatchard plot with the modified McGhee and von Hippel model for a finite one-dimensional homogeneous lattice and nonspecific binding of ligands to duplex DNA yields the intrinsic binding constant, the number of lattice sites occluded by a bound ligand, and the cooperativity parameter of 3.6 × 10⁵ M^-1, 4.0, and 8.1, respectively. The occluded site size of 4 indicates that moieties of the EG intercalate into the adjacent base pairs of the duplex DNA with a gap of 1 intercalation site between EG binding sites, as expected for a bifunctional molecule. Interestingly, at high [EG]/[base pair], the intercalation is disrupted. A model is proposed based on the fluorescence spectrum where the formation of anti-parallel stacked chains of EGs bound externally to the duplex DNA occur at these high ratios.

Recent Advances on the Multiplex Molecular Detection of Plant Viruses and Viroids

Plant viruses are still one of the main contributors to economic losses in agriculture. It has been estimated that plant viruses can cause as much as 50 billion euros loss worldwide, per year. This situation may be worsened by recent climate change events and the associated changes in disease epidemiology. Reliable and early detection methods are still one of the main and most effective actions to develop control strategies for plant viral diseases. During the last years, considerable progress has been made to develop tools with high specificity and low detection limits for use in the detection of these plant pathogens. Time and cost reductions have been some of the main objectives pursued during the last few years as these increase their feasibility for routine use. Among other strategies, these objectives can be achieved by the simultaneous detection and (or) identification of several viruses in a single assay. Nucleic acid-based detection techniques are especially suitable for this purpose. Polyvalent detection has allowed the detection of multiple plant viruses at the genus level. Multiplexing RT polymerase chain reaction (PCR) has been optimized for the simultaneous detection of more than 10 plant viruses/viroids. In this short review, we provide an update on the progress made during the last decade on techniques such as multiplex PCR, polyvalent PCR, non-isotopic molecular hybridization techniques, real-time PCR, and array technologies to allow simultaneous detection of multiple plant viruses. Also, the potential and benefits of the powerful new technique of deep sequencing/next-generation sequencing are described.

A Fast and Reliable Real-Time PCR Method for Detection of Ten Animal Species in Meat Products

Species substitution in meat products is a common problem reported worldwide. This type of food fraud is, typically, an intentional act for economic gain, using sources of low-priced meats in high-value meat products. Consequences include economic, health, and religious concerns. Highly sensitive and efficient techniques are thus required to detect meat species. This paper describes a method based on real-time PCR to detect 10 animal species (Bos taurus, Sus scrofa, Ovis aries, Capra hircus, Gallus gallus, Meleagris gallopavo, Bubalus bubalis, Equus caballus, Felis catus, and Canis familiaris) in meat product. The method combines species-specific and universal (used here as internal positive control) primers, and applies melt curve analysis for amplicon checking. Method accuracy was evaluated on 46 experimental meat mixtures and all species were correctly identified in all cases, at 1% test sensitivity. Analysis of 14 commercial meat products revealed that 6 of 14 samples had nondeclared bovine and/or chicken material. We performed an interlaboratory comparison using the reference meat mixtures and commercial samples, achieving 100% of reproducibility. The developed test proved to be effective and reliable for routine analysis of meat products.

PRACTICAL APPLICATION

This paper describes a fast and reliable method for species detection in meat products based on real-time PCR. It can be applied for analysis of in natura or processed meat. The method proposed here can play an important role in controlling the origin of meat products, ensuring their quality and safety for the entire food industry-producers to consumers.

Development of a Quantitative Loop-Mediated Isothermal Amplification Assay for the Rapid Detection of Novel Goose Parvovirus

An infectious disease characterized with short bills and protruding tongues has attacked to meat ducks in China since March 2015, which has caused ducks poor growth and enormous economic losses to duck industry of China. It was eventually proved to be caused by parvovirus after pathogen isolation and identification. As the genomic sequence analysis showed, this pathogen shared 90.8-94.6% of nucleotide identity with goose parvovirus (GPV), and it was called duck-origin novel goose parvovirus (N-GPV). In this study, a quantitative loop-mediated isothermal amplification (qLAMP) assay was developed for the rapid diagnosis of N-GPV. A set of four specific primers, two inner and two outer, were designed targeting at VP3 gene, which could be completed within 60 min at 65°C in water bath or on a real-time PCR instrument for quantitative analysis. Specificity test of LAMP assay showed that there was no cross-reactivity between N-GPV and other duck pathogens, and the detection limit of qLAMP assay was 1.0 × 10² copies/μL. The repeatability of this method was confirmed by inter-assay and intra-assay tests with variability ranging from 0.74 to 2.25%. The results have indicated that the qLAMP assay was a simple, rapid, accurate, sensitive, and specific method for detecting N-GPV, especially on field detection.

Blending DNA binding dyes to improve detection in real-time PCR

The success of real-time PCR (qPCR) analysis is partly limited by the presence of inhibitory compounds in the nucleic acid samples. For example, humic acid (HA) from soil and aqueous sediment interferes with amplification and also quenches the fluorescence of double-stranded (ds) DNA binding dyes, thus hindering amplicon detection. We aimed to counteract the HA fluorescence quenching effect by blending complementary dsDNA binding dyes, thereby elevating the dye saturation levels and increasing the fluorescence signals. A blend of the four dyes EvaGreen, ResoLight, SYBR Green and SYTO9 gave significantly higher fluorescence intensities in the presence and absence of HA, compared with the dyes applied separately and two-dye blends. We propose blending of dyes as a generally applicable means for elevating qPCR fluorescence signals and thus enabling detection in the presence of quenching substances.

Values of molecular markers in the differential diagnosis of thyroid abnormalities

INTRODUCTION

Thyroid cancer (TC), follicular adenoma (FA) and Hashimoto's thyroiditis (HT) are three of the most frequently reported abnormalities that affect the thyroid gland. A frequent co-occurrence along with similar histopathological features is observed between TC and FA as well as between TC and HT. The conventional diagnostic methods such as histochemical analysis present complications in differential diagnosis when these abnormalities occur simultaneously. Hence, the authors recognize novel methods based on screening genetic defects of thyroid abnormalities as viable diagnostic and prognostic methods that could complement the conventional methods.

METHODS

We have extensively reviewed the existing literature on TC, FA and HT and also on three genes, namely braf, nras and ret/ptc, that could be used to differentially diagnose the three abnormalities. Emphasis was also given to the screening methods available to detect the said molecular markers.

RESULTS AND CONCLUSION

It can be conferred from the analysis of the available data that the utilization of braf, nras and ret/ptc as markers for the therapeutic evaluation of FA and HT is debatable. However, molecular screening for braf, nras and ret/ptc mutations proves to be a conclusive method that could be employed to differentially diagnose TC from HT and FA in the instance of a suspected co-occurrence. Thyroid cancer patients can be highly benefited from the screening for the said genetic markers, especially the braf gene due to its diagnostic value as well as due to the availability of personalized medicine targeted specifically for braf mutants.

Optimization of Diamond Nucleic Acid Dye for quantitative PCR

Here, we evaluate Diamond Nucleic Acid Dye (DD) for use in quantitative PCR (qPCR) applications. Although DD is a commercially available stain for detection of DNA separated by gel electrophoresis, its use as a detection dye in qPCR has yet to be described. To determine if DD can be used in qPCR, we investigated its inhibitory effects on qPCR at concentrations ranging 0.1–2.5×. Serial dilution of DNA was used to determine the efficiency, sensitivity, and linearity of DD-generated qPCR data in comparison to other commonly used fluorescent dyes such as SYBR Green (SG), EvaGreen (EG), and BRYT Green (BG). DD was found to be comparable with other dyes for qPCR applications, with an R2 value >0.9 and an efficiency of 0.83. Mitochondrial DNA (mtDNA) target signals were successfully produced by DD over a DNA dilution range of ∼28 ng— 0.28 pg, demonstrating comparable sensitivity to the other dyes investigated. Cq values obtained using DD were lower than those using EG by almost 7 cycles. We conclude that Diamond Nucleic Acid Dye is a cheaper, less toxic alternative for qPCR applications.

Use of the melting curve assay as a means for high-throughput quantification of Illumina sequencing libraries

Background. Multiplexed sequencing is commonly performed on massively parallel short-read sequencing platforms such as Illumina, and the efficiency of library normalisation can affect the quality of the output dataset. Although several library normalisation approaches have been established, none are ideal for highly multiplexed sequencing due to issues of cost and/or processing time.

Methods. An inexpensive and high-throughput library quantification method has been developed, based on an adaptation of the melting curve assay. Sequencing libraries were subjected to the assay using the Bio-Rad Laboratories CFX Connect^TM Real-Time PCR Detection System. The library quantity was calculated through summation of reduction of relative fluorescence units between 86 and 95 °C.

Results.PCR-enriched sequencing libraries are suitable for this quantification without pre-purification of DNA. Short DNA molecules, which ideally should be eliminated from the library for subsequent processing, were differentiated from the target DNA in a mixture on the basis of differences in melting temperature. Quantification results for long sequences targeted using the melting curve assay were correlated with those from existing methods (R² > 0.77), and that observed from MiSeq sequencing (R² = 0.82).

Discussion.The results of multiplexed sequencing suggested that the normalisation performance of the described method is equivalent to that of another recently reported high-throughput bead-based method, BeNUS. However, costs for the melting curve assay are considerably lower and processing times shorter than those of other existing methods, suggesting greater suitability for highly multiplexed sequencing applications.

Comparison of fluorescent intercalating dyes for quantitative loop-mediated isothermal amplification (qLAMP)

Real-time or quantitative loop-mediated isothermal amplification (qLAMP) is a promising technique for the accurate detection of pathogens in organisms and the environment. Here we present a comparative study of the performance of six fluorescent intercalating dyes-SYTO-9, SYTO-13, SYTO-82, SYBR Green I, SYBR Gold, EvaGreen-in three different qLAMP model systems. SYTO-9 and SYTO-82, which had the best results, were used for additional enzyme and template titration studies. SYTO-82 demonstrated the best combination of time-to-threshold (Tt) and signal-to-noise ratio (SNR).

Trends and advances in food analysis by real-time polymerase chain reaction

Analyses to ensure food safety and quality are more relevant now because of rapid changes in the quantity, diversity and mobility of food. Food-contamination must be determined to maintain health and up-hold laws, as well as for ethical and cultural concerns. Real-time polymerase chain reaction (RT-PCR), a rapid and inexpensive quantitative method to detect the presence of targeted DNA-segments in samples, helps in determining both accidental and intentional adulterations of foods by biological contaminants. This review presents recent developments in theory, techniques, and applications of RT-PCR in food analyses, RT-PCR addresses the limitations of traditional food analyses in terms of sensitivity, range of analytes, multiplexing ability, cost, time, and point-of-care applications. A range of targets, including species of plants or animals which are used as food ingredients, food-borne bacteria or viruses, genetically modified organisms, and allergens, even in highly processed foods can be identified by RT-PCR, even at very low concentrations. Microfluidic RT-PCR eliminates the separate sample-processing step to create opportunities for point-of-care analyses. We also cover the challenges related to using RT-PCR for food analyses, such as the need to further improve sample handling.

Monitoring the freshness of fish: development of a qPCR method applied to MAP chilled whiting

BACKGROUND

Monitoring of early stages of freshness decay is a major issue for the fishery industry to guarantee the best quality for this highly perishable food matrix. Numerous techniques have been developed, but most of them have the disadvantage of being reliable only either in the last stages of fish freshness or for the analysis of whole fish. This study describes the development of a qPCR method targeting the torA gene harboured by fish spoilage microorganisms. torA encodes an enzyme that leads to the production of trimethylamine responsible for the characteristic spoiled-fish odour.

RESULTS

A degenerate primer pair was designed. It amplified torA gene of both Vibrio and Photobacterium with good efficiencies on 7-log DNA dilutions. The primer pair was used during a shelf-life monitoring study achieved on modified atmosphere packed, chilled, whiting (Merlangius merlangus) fillets. The qPCR approach allows the detection of an increase of torA copies throughout the storage of fillets in correlation with the evolution of both total volatile basic nitrogen (-0.86) and trimethylamine concentrations (-0.81), known as spoilage markers.

CONCLUSION

This study described a very promising, sensitive, reliable, time-effective, technique in the field of freshness characterisation of processed fish.

MeltMan: Optimization, Evaluation, and Universal Application of a qPCR System Integrating the TaqMan qPCR and Melting Analysis into a Single Assay

In the present work, we optimised and evaluated a qPCR system integrating 6-FAM (6-carboxyfluorescein)-labelled TaqMan probes and melting analysis using the SYTO 82 (S82) DNA binding dye in a single reaction. We investigated the influence of the S82 on various TaqMan and melting analysis parameters and defined its optimal concentration. In the next step, the method was evaluated in 36 different TaqMan assays with a total of 729 paired reactions using various DNA and RNA templates, including field specimens. In addition, the melting profiles of interest were correlated with the electrophoretic patterns. We proved that the S82 is fully compatible with the FAM-TaqMan system. Further, the advantages of this approach in routine diagnostic TaqMan qPCR were illustrated with practical examples. These included solving problems with flat or other atypical amplification curves or even false negativity as a result of probe binding failure. Our data clearly show that the integration of the TaqMan qPCR and melting analysis into a single assay provides an additional control option as well as the opportunity to perform more complex analyses, get more data from the reactions, and obtain analysis results with higher confidence.