Detection of single-nucleotide polymorphisms in Plasmodium falciparum by PCR primer extension and lateral flow immunoassay

The Revolution of Lateral Flow Assay in the Field of AMR Detection

The global spread of antimicrobial resistant (AMR) bacteria represents a considerable public health concern, yet their detection and identification of their resistance mechanisms remain challenging. Optimal diagnostic tests should provide rapid results at low cost to enable implementation in any microbiology laboratory. Lateral flow assays (LFA) meet these requirements and have become essential tools to combat AMR. This review presents the versatility of LFA developed for the AMR detection field, with particular attention to those directly triggering β-lactamases, their performances, and specific limitations. It considers how LFA can be modified by detecting not only the enzyme, but also its β-lactamase activity for a broader clinical sensitivity. Moreover, although LFA allow a short time-to-result, they are generally only implemented after fastidious and time-consuming techniques. We present a sample processing device that shortens and simplifies the handling of clinical samples before the use of LFA. Finally, the capacity of LFA to detect amplified genetic determinants of AMR by isothermal PCR will be discussed. LFA are inexpensive, rapid, and efficient tools that are easy to implement in the routine workflow of laboratories as new first-line tests against AMR with bacterial colonies, and in the near future directly with biological media.

Hapten-labeled fusion-polymerase chain reaction of multiple marker genes for the application of immunochromatographic test

A variety of methods have been reported using polymerase chain reaction (PCR)-based nucleic acid testing (NAT) because of its potential to be used in highly sensitive inspection systems. Among these NATs, fusion-PCR (also called as overlap-extension-PCR) has been focused on this study and adopted to generate the fused amplicon composed of plural marker gene fragments for detection. Generally, conventional agarose gel electrophoresis followed by gel staining is employed to check the PCR results. However, these are time-consuming processes that use specific equipment. To overcome these disadvantages, the immunochromatographic test (ICT) for the detection of PCR amplicons with hapten-labels that were generated by PCR using hapten-labeled primers was also adopted in this study. Based on these concepts, we constructed the systems of hapten-labeled fusion-PCR (HL-FuPCR) followed by ICT (HL-FuPCR-ICT) for the two and three marker genes derived from pathogenic microbe. As a result, we successfully developed a two marker genes system for the pathogenic influenza A virus and a three marker genes system for the penicillin-resistant Streptococcus pneumoniae. These detection systems of HL-FuPCR-ICT are characterized by simple handling and rapid detection within few minutes, and also showed the results as clear lines. Thus, the HL-FuPCR-ICT system introduced in this study has potential for use as a user-friendly inspection tool with the advantages especially in the detection of specific strains or groups expressing the characteristic phenotype(s) such as antibiotic resistance and/or high pathogenicity even in the same species.

Diagnosing the drug resistance signature in Plasmodium falciparum: a review from contemporary methods to novel approaches

The genome sequence project of the human malaria parasite Plasmodium falciparum reveal variations in the parasite DNA sequence. Most of these variations are single nucleotide polymorphism (SNP). A high frequency of single nucleotide polymorphism (SNP) in the Plasmodium falciparum population is usually a benchmark for anti-malarial resistance which allows parasites to be elusive to the chemotherapeutic agents, vaccine and vector control strategies, resulting in the leading cause of morbidity and mortality globally. The high density of drug resistance signature markers such as pfcrt,pfmdr1, pfdhps, pfdhfr, pfkelch13, pfatpase6 and pfmrp1 in the genome opens up a scope for the study of the genetic basis of this elusive parasite. The precise and prompt diagnosis of resistance strains of parasite plays vital role in malaria elimination program.This review probably shed light on contemporary SNP diagnostic tools used in molecular surveillance of Plasmodium falciparum drug resistance in terms of mechanism, reaction modalities, and development with their virtues and shortcomings.

Loop-Primer Endonuclease Cleavage-Loop-Mediated Isothermal Amplification Technology for Multiplex Pathogen Detection and Single-Nucleotide Polymorphism Identification

Loop-mediated isothermal amplification (LAMP) provides effective diagnostic technology for infectious disease pathogen identification and is compatible with inexpensive instrumentation for use in disease-prevalent developing regions. However, simultaneous multiple-target detection and single-nucleotide polymorphism (SNP) identification, essential properties of nucleic acid diagnostics, are difficult to achieve using LAMP. This study introduces loop-primer endonuclease cleavage (LEC)-LAMP, a singleplex or multiplex LAMP technology with single-base specificity for variable SNP identification. We developed a singleplex LEC-LAMP Neisseria meningitidis assay that demonstrated complete analytical specificity and a limit of detection of 3.1 genome copies per reaction. Small-scale clinical testing of this assay demonstrated 100% diagnostic specificity and sensitivity when assessed with anonymized DNA extracts from confirmed cases of bacterial meningitis infection. The single-base specificity of this assay indicated effective SNP identification properties when challenged with DNA templates containing SNPs located within a specific six-base region. This assay was modified to generate an allele-specific LEC-LAMP N. meningitidis assay that successfully demonstrated single-tube differentiation of wild-type and mutant allele templates. The singleplex assay was further modified to generate a multiplex LEC-LAMP assay that successfully demonstrated simultaneous multiple-target detection of three bacterial targets, N. meningitidis, Streptococcus pneumonia, and Hemophilus influenzae. LEC-LAMP is the first report of single-tube, real-time, singleplex or multiplex LAMP technology with single-base specificity for variable SNP identification.

Current methods for the detection of antimalarial drug resistance in Plasmodium parasites infecting humans

Malaria is the world's deadliest parasitic disease. Great progress has been made in the fight against malaria over the past two decades, but this has recently begun to plateau, in part due to the global development of antimalarial drug resistance. The ability to track drug resistance is necessary to achieve progress in treatment, disease surveillance and epidemiology, which has prompted the development of advanced diagnostic methods. These new methods provide unprecedented access to information that can help to guide public health policies. Development of new technologies increases the potential for high throughput and reduced costs of diagnostic tests; improving the accessibility of tools to investigate the forces driving disease dynamics and, ultimately, clinical outcomes for malaria patients and public health. This literature review provides a summary of the methods currently available for the detection of antimalarial drug resistance from the examination of patients' blood samples. While no single method is perfect for every application, many of the newly developed methods give promise for more reliable and efficient characterisation of Plasmodium resistance in a range of settings. By exploiting the strengths of the tools available, we can develop a deeper understanding of the evolutionary and spatiotemporal dynamics of this disease. This will translate into more effective disease control, better-informed policy, and more timely and successful treatment for malaria patients.

Six decades of lateral flow immunoassay: from determining metabolic markers to diagnosing COVID-19

Technologies based on lateral flow immunoassay (LFIA), known in some countries of the world as immunochromatographic tests, have been successfully used for the last six decades in diagnostics of many diseases and conditions as they allow rapid detection of molecular ligands in biosubstrates. The popularity of these diagnostic platforms is constantly increasing in healthcare facilities, particularly those facing limited budgets and time, as well as in household use for individual health monitoring. The advantages of these low-cost devices over modern laboratory-based analyzers come from their availability, opportunity of rapid detection, and ease of use. The attractiveness of these portable diagnostic tools is associated primarily with their high analytical sensitivity and specificity, as well as with the easy visual readout of results. These qualities explain the growing popularity of LFIA in developing countries, when applied at small hospitals, in emergency situations where screening and monitoring health condition is crucially important, and as well as for self-testing of patients. These tools have passed the test of time, and now LFIA test systems are fully consistent with the world's modern concept of ‘point-of-care testing’, finding a wide range of applications not only in human medicine, but also in ecology, veterinary medicine, and agriculture. The extensive opportunities provided by LFIA contribute to the continuous development and improvement of this technology and to the creation of new-generation formats. This review will highlight the modern principles of design of the most widely used formats of test-systems for clinical laboratory diagnostics, summarize the main advantages and disadvantages of the method, as well as the current achievements and prospects of the LFIA technology. The latest innovations are aimed at improving the analytical performance of LFIA platforms for the diagnosis of bacterial and viral infections, including COVID-19.

Detecting sequence variants in clinically important protozoan parasites

Second and third generation sequencing methods are crucial for population genetic studies, and variant detection is a popular approach for exploiting this sequence data. While mini- and microsatellites are historically useful markers for studying important Protozoa such as Toxoplasma and Plasmodium spp., detecting non-repetitive variants such as those found in genes can be fundamental to investigating a pathogen's biology. These variants, namely single nucleotide polymorphisms and insertions and deletions, can help elucidate the genetic basis of an organism's pathogenicity, identify selective pressures, and resolve phylogenetic relationships. They also have the added benefit of possessing a comparatively low mutation rate, which contributes to their stability. However, there is a plethora of variant analysis tools with nuanced pipelines and conflicting recommendations for best practise, which can be confounding. This lack of standardisation means that variant analysis requires careful parameter optimisation, an understanding of its limitations, and the availability of high quality data. This review explores the value of variant detection when applied to non-model organisms such as clinically important protozoan pathogens. The limitations of current methods are discussed, including special considerations that require the end-users' attention to ensure that the results generated are reproducible, and the biological conclusions drawn are valid.

Molecular assays for antimalarial drug resistance surveillance: A target product profile

Antimalarial drug resistance is a major constraint for malaria control and elimination efforts. Artemisinin-based combination therapy is now the mainstay for malaria treatment. However, delayed parasite clearance following treatment with artemisinin derivatives has now spread in the Greater Mekong Sub region and may emerge or spread to other malaria endemic regions. This spread is of great concern for malaria control programmes, as no alternatives to artemisinin-based combination therapies are expected to be available in the near future. There is a need to strengthen surveillance systems for early detection and response to the antimalarial drug resistance threat. Current surveillance is mainly done through therapeutic efficacy studies; however these studies are complex and both time- and resource-intensive. For multiple common antimalarials, parasite drug resistance has been correlated with specific genetic mutations, and the molecular markers associated with antimalarial drug resistance offer a simple and powerful tool to monitor the emergence and spread of resistant parasites. Different techniques to analyse molecular markers associated with antimalarial drug resistance are available, each with advantages and disadvantages. However, procedures are not adequately harmonized to facilitate comparisons between sites. Here we describe the target product profiles for tests to analyse molecular markers associated with antimalarial drug resistance, discuss how use of current techniques can be standardised, and identify the requirements for an ideal product that would allow malaria endemic countries to provide useful spatial and temporal information on the spread of resistance.

Tools for surveillance of anti-malarial drug resistance: an assessment of the current landscape

To limit the spread and impact of anti-malarial drug resistance and react accordingly, surveillance systems able to detect and track in real-time its emergence and spread need to be strengthened or in some places established. Currently, surveillance of anti-malarial drug resistance is done by any of three approaches: (1) in vivo studies to assess the efficacy of drugs in patients; (2) in vitro/ex vivo studies to evaluate parasite susceptibility to the drugs; and/or (3) molecular assays to detect validated gene mutations and/or gene copy number changes that are associated with drug resistance. These methods are complementary, as they evaluate different aspects of resistance; however, standardization of methods, especially for in vitro/ex vivo and molecular techniques, is lacking. The World Health Organization has developed a standard protocol for evaluating the efficacy of anti-malarial drugs, which is used by National Malaria Control Programmes to conduct their therapeutic efficacy studies. Regional networks, such as the East African Network for Monitoring Antimalarial Treatment and the Amazon Network for the Surveillance of Antimalarial Drug Resistance, have been set up to strengthen regional capacities for monitoring anti-malarial drug resistance. The Worldwide Antimalarial Resistance Network has been established to collate and provide global spatial and temporal trends information on the efficacy of anti-malarial drugs and resistance. While exchange of information across endemic countries is essential for monitoring anti-malarial resistance, sustainable funding for the surveillance and networking activities remains challenging. The technology landscape for molecular assays is progressing quite rapidly, and easy-to-use and affordable new techniques are becoming available. They also offer the advantage of high throughput analysis from a simple blood spots obtained from a finger prick. New technologies combined with the strengthening of national reference laboratories in malaria-endemic countries through standardized protocols and training plus the availability of a proficiency testing programme, would contribute to the improvement and sustainability of anti-malarial resistance surveillance networks worldwide.

Development of a dry-reagent-based nucleic acid-sensing platform by coupling thermostabilised LATE-PCR assay to an oligonucleotide-modified lateral flow biosensor

In this study, we report for the first time the development of a dry-reagent-based nucleic acid-sensing platform by combining a thermostabilised linear-after-the-exponential (LATE)-PCR assay with a one-step, hybridisation-based nucleic acid lateral flow biosensor. The nucleic acid-sensing platform was designed to overcome the need for stringent temperature control during transportation or storage of reagents and reduces the dependency on skilled personnel by decreasing the overall assay complexity and hands-on time. The platform was developed using toxigenic Vibrio cholerae as the model organism due to the bacterium's propensity to cause epidemic and pandemic cholera. The biosensor generates result which can be visualised with the naked eyes and the limit of detection was found to be 1pg of pure genomic DNA and 10CFU/ml of toxigenic V. cholerae. The dry-reagent-based nucleic acid-sensing platform was challenged with 95 toxigenic V. cholerae, 7 non-toxigenic V. cholerae and 66 other bacterial strains in spiked stool sample and complete agreement was observed when the results were compared to that of monosialoganglioside (GM1)-ELISA. Heat-stability of the thermostabilised LATE-PCR reaction mixes at different storage temperatures (4-56°C) was investigated for up to 90days. The dry-reagent-based genosensing platform with ready-to-use assay components provides an alternative method for sequence-specific detection of nucleic acid without any cold chain restriction that is associated with conventional molecular amplification techniques.