Single-use, electricity-free amplification device for detection of HIV-1

Multiplexing LAMP Assays: A Methodological Review and Diagnostic Application

The loop-mediated isothermal amplification (LAMP) technique is a great alternative to PCR-based methods, as it is fast, easy to use and works with high sensitivity and specificity without the need for expensive instruments. However, one of the limitations of LAMP is difficulty in achieving the simultaneous detection of several targets in a single tube, as the methodologies that allow this rely on fluorogenic probes containing specific target sequences, complicating their adaptation and the optimization of assays. Here, we summarize different methods for the development of multiplex LAMP assays based on sequence-specific detection, illustrated with a schematic representation of the technique, and evaluate their practical application based on the real-time detection and quantification of results, the possibility to visualize the results at a glance, the prior stabilization of reaction components, promoting the point-of-care use, the maximum number of specific targets amplified, and the validation of the technique in clinical samples. The various LAMP multiplexing methodologies differ in their operating conditions and mechanism. Each methodology has its advantages and disadvantages, and the choice among them will depend on specific application interests.

A Diagnostic Chip for the Colorimetric Detection of Legionella pneumophila in Less than 3 h at the Point of Need

Legionella pneumophila has been pinpointed by the World Health Organization as the highest health burden of all waterborne pathogens in the European Union and is responsible for many disease outbreaks around the globe. Today, standard analysis methods (based on bacteria culturing onto agar plates) need several days (~12) in specialized analytical laboratories to yield results, not allowing for timely actions to prevent outbreaks. Over the last decades, great efforts have been made to develop more efficient waterborne pathogen diagnostics and faster analysis methods, requiring further advancement of microfluidics and sensors for simple, rapid, accurate, inexpensive, real-time, and on-site methods. Herein, a lab-on-a-chip device integrating sample preparation by accommodating bacteria capture, lysis, and DNA isothermal amplification with fast (less than 3 h) and highly sensitive, colorimetric end-point detection of L. pneumophila in water samples is presented, for use at the point of need. The method is based on the selective capture of viable bacteria on on-chip-immobilized and -lyophilized antibodies, lysis, the loop-mediated amplification (LAMP) of DNA, and end-point detection by a color change, observable by the naked eye and semiquantified by computational image analysis. Competitive advantages are demonstrated, such as low reagent consumption, portability and disposability, color change, storage at RT, and compliance with current legislation.

Compact Point-of-Care Device for Self-Administered HIV Viral Load Tests from Whole Blood

Human immunodeficiency virus (HIV) is a significant problem to consider as it can lead to acquired immune deficiency syndrome (AIDS). Fortunately, AIDS is manageable through antiretroviral therapy (ART). However, frequent viral load monitoring is needed to monitor the effectiveness of the therapy. The current reverse transcription-polymerase chain reaction (RT-PCR) viral load monitoring is highly effective, but is challenged by being resource-intensive and inaccessible, and its turnaround time does not meet demand. An unmet need exists for an affordable, rapid, and user-friendly point-of-care device that could revolutionize and ensure therapeutic effectiveness, particularly in resource-limited settings. In this work, we explored a point-of-care HIV viral load device to address this need. This device can perform streamlined plasma separation, viral RNA extraction, and real-time reverse transcription loop-mediated isothermal amplification (RT-LAMP) semiquantitative testing in an ultracompact device. We developed an absorption-based membrane plasma separation method suitable for finger-prick blood samples, achieving an efficiency of 80%. We also designed a syringe-based RNA extraction method for on-site plasma processing with a viral recovery efficiency of 86%. We created a portable device with a smartphone interface for real-time semiquantitative RT-LAMP, which is useful for monitoring viral load. The device uses lyophilized reagents, processed with our lyophilization method, which remain stable for 16 weeks. The device can accurately categorize viral load into low, medium, and high categories with 95% accuracy. We believe this point-of-care HIV self-test device, offering convenience and long-term storage, could aid patients in home-based ART treatment monitoring.

Molecular point-of-care devices for the diagnosis of infectious diseases in resource-limited settings - A review of the current landscape, technical challenges, and clinical impact

Molecular point-of-care (POC) tests offer high sensitivity, rapid turnaround times, relative ease of use, and the convenience of laboratory-grade testing in the absence of formal laboratory spaces and equipment, making them appealing options for infectious disease diagnosis in resource-limited settings. In this review, we discuss the role and potential of molecular POC tests in resource-limited settings and their associated logistical challenges. We discuss U.S. Food and Drug Administration approval, Clinical Laboratory Improvement Amendments complexity levels, and the REASSURED criteria as a starting point for assessing options currently available inside and outside of the United States. We then present POC tests currently in research and development phases that have potential for commercialization and implementation in limited-resource settings. Finally, we review published studies that have assessed the clinical impact of molecular POC testing in limited- and moderate-resource settings.

Current and Future Advances in the Detection and Surveillance of Biosecurity-Relevant Equine Bacterial Diseases Using Loop-Mediated Isothermal Amplification (LAMP)

Horses play an important role throughout the world, whether for work, culture, or leisure, providing an ever-growing significant contribution to the economy. The increase in importation and movement of horses, both nationally and internationally, has inevitably allowed for the global equine industry to grow. Subsequently, however, the potential for transmission of fatal equine bacterial diseases has also escalated, and devasting outbreaks continue to occur. To prevent such events, disease surveillance and diagnosis must be heightened throughout the industry. Current common, or "gold-standard" techniques, have shown to be inadequate at times, thus requiring newer technology to impede outbreaks. Loop-mediated isothermal amplification (LAMP) has proven to be a reliable, rapid, and accessible tool in both diagnostics and surveillance. This review will discuss equine bacterial diseases of biosecurity relevance and their current diagnostic approaches, as well as their respective LAMP assay developments. Additionally, we will provide insight regarding newer technology and advancements associated with this technique and their potential use for the outlined diseases.

Microfluidic Devices for HIV Diagnosis and Monitoring at Point-of-Care (POC) Settings

Human immunodeficiency virus (HIV) is a global epidemic; however, many individuals are able to obtain treatment and manage their condition. Progression to acquired immunodeficiency syndrome (AIDS) occurs during late-stage HIV infection, which compromises the immune system, making it susceptible to infections. While there is no cure, antiretroviral therapy can be used provided that detection occurs, preferably during the early phase. However, the detection of HIV is expensive and resource-intensive when tested with conventional methods, such as flow cytometry, polymerase chain reaction (PCR), or enzyme-linked immunosorbent assays (ELISA). Improving disease detection in resource-constrained areas requires equipment that is affordable, portable, and can deliver rapid results. Microfluidic devices have transformed many benchtop techniques to on-chip detection for portable and rapid point-of-care (POC) testing. These devices are cost-effective, sensitive, and rapid and can be used in areas lacking resources. Moreover, their functionality can rival their benchtop counterparts, making them efficient for disease detection. In this review, we discuss the limitations of currently used conventional HIV diagnostic assays and provide an overview of potential microfluidic technologies that can improve HIV testing in POC settings.

Fingerpick Blood-Based Nucleic Acid Testing on A USB Interfaced Device towards HIV self-testing

HIV self-testing is an emerging innovative approach that allows individuals who want to know their HIV status to collect their own specimen, perform a test, and interpret the results privately. Existing HIV self-testing methods rely on rapid diagnostic tests (RDTs) to detect the presence of HIV-1/2 antibodies, which could miss a significant portion of asymptomatic carriers during the window period. In this work, we present a fully integrated nucleic acid testing (NAT) device towards streamlined HIV self-testing using 100 μL finger-prick whole blood. The device consists of a ready-to-use microfluidic reagent cartridge and an ultra-compact NAT-on-USB analyzer. The test requires simple steps from the user to drop the finger-prick blood sample into a collection tube with lysis buffer and load the lysate onto the microfluidic cartridge, and the testing result can be easily read out by a custom-built graphical user interface (GUI). The microfluidic cartridge and the analyzer automatically handle the complexity of sample preparation, purification, and real-time reverse-transcription loop-mediated isothermal amplification (RT-LAMP). With a turnaround time of ∼60 min, we achieved a limit of detection (LoD) of 214 viral RNA copies/mL of whole blood at a 95% confidence level. Due to its ease of use and high sensitivity, we anticipate the HIV NAT-on-USB device would be particularly useful for the high-risk populations seeking private self-testing at the early stages of exposure.

An HFman probe-based reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay for HIV-1 detection

Loop-mediated isothermal amplification (LAMP) is suitable for the development of a rapid and cost-effective nucleic acid technique for point of care (POC) applications. However, LAMP methods often generate non-specific amplification, therefore inevitably resulting in false positive results especially when sequence-independent dyes are used to indirectly reflect the results. In this study, we established and optimized a reverse transcription LAMP (RT-LAMP) assay with a high-fidelity DNA polymerase-mediated fluorescent probe (HFman probe) for human immunodeficiency virus-1 (HIV-1) detection. The assay showed high sensitivity and specificity. Using 101 plasma samples with different HIV-1 viral load, we demonstrated that our assay can detect the major HIV-1 subtypes circulating in China, including CRF01_AE, CRF07_BC, CRF08_BC, CRF55_01B, and unique recombinant forms (URFs). We also compared our assay with an approved commercial real-time quantitative polymerase chain reaction (RT-qPCR) kit and found the sensitivity, specificity and consistency was 88.8%, 100% and 89.1%, respectively. The HFman probe-based RT-LAMP assay is a high specific detection method that is rapid, variant-tolerant and simple to operate, and thus is of great significance for timely disclosure of HIV status and rapid POC diagnosis.

Bridging the gap between development of point-of-care nucleic acid testing and patient care for sexually transmitted infections

The incidence rates of sexually transmitted infections (STIs), including the four major curable STIs - chlamydia, gonorrhea, trichomoniasis and, syphilis - continue to increase globally, causing medical cost burden and morbidity especially in low and middle-income countries (LMIC). There have seen significant advances in diagnostic testing, but commercial antigen-based point-of-care tests (POCTs) are often insufficiently sensitive and specific, while near-point-of-care (POC) instruments that can perform sensitive and specific nucleic acid amplification tests (NAATs) are technically complex and expensive, especially for LMIC. Thus, there remains a critical need for NAAT-based STI POCTs that can improve diagnosis and curb the ongoing epidemic. Unfortunately, the development of such POCTs has been challenging due to the gap between researchers developing new technologies and healthcare providers using these technologies. This review aims to bridge this gap. We first present a short introduction of the four major STIs, followed by a discussion on the current landscape of commercial near-POC instruments for the detection of these STIs. We present relevant research toward addressing the gaps in developing NAAT-based STI POCT technologies and supplement this discussion with technologies for HIV and other infectious diseases, which may be adapted for STIs. Additionally, as case studies, we highlight the developmental trajectory of two different POCT technologies, including one approved by the United States Food and Drug Administration (FDA). Finally, we offer our perspectives on future development of NAAT-based STI POCT technologies.

An Ultracompact Real-Time Fluorescence Loop-Mediated Isothermal Amplification (LAMP) Analyzer

Low-cost access to the highly sensitive and specific detection of the pathogen in the field is a crucial attribute for the next generation point-of-care (POC) platforms. In this work, we developed a real-time fluorescence nucleic acid testing device with automated and scalable sample preparation capability for field malaria diagnosis. The palm-sized battery-powered analyzer equipped with a disposable microfluidic reagent compact disc described in the companion Chap. 16 which facilitates four isothermal nucleic acid tests in parallel from raw blood samples to answer. The platform has a user-friendly interface such as touchscreen LCD and smartphone data connectivity for on-site and remote healthcare delivery, respectively. The chapter mainly focuses on describing integration procedures of the real-time fluorescence LAMP analyzer and the validation of its subsystems. The device cost is significantly reduced compared to the commercial benchtop real-time machine and other existing POC platforms. As a platform technology, self-sustainable, portable, low-cost, and easy-to-use analyzer design should create a new paradigm of molecular diagnosis toward a variety of infectious diseases at the point of need.

Portable Molecular Diagnostics Device for Identification of Asini Corii Colla by Loop-Mediated Isothermal Amplification

Asini Corii Colla (ACC; donkey-hide glue) is one of the most valuable tonic traditional Chinese medicines. Because of the large demand for gelatinous Chinese medicines, bovine or swine skin was sometimes used to make adulterated gelatine in recent decades. Food chemicals can greatly harm people’s health, and detecting chemicals in foods is extremely important. A loop-mediated isothermal amplification (LAMP) device with smartphone detection is demonstrated in this study for detecting the DNA of Asini Corii Colla. The complete system is composed of a hand-held box equipped with a smartphone, a cartridge heater, an ultraviolet LED, a disposable reaction tube, and a homemade thermal module. All the processes are powered by a set of rechargeable batteries. Comprehensive experiments of measuring temperature profiles are presented, which showed the accuracy of temperature under thermal control is less than 0.5 °C. By implementing one heating module with an ATmega328p-au microcontroller in the device, the DNA mixture is heated directly up to the reaction temperature within 5 min. Next, a DNA segment of Asini Corii Colla is utilized to evaluate the sensitivity of the DNA amplification in the portable device. A limit of detection to a concentration of 10−4 ng/μL is achieved. Real-time detection of Asini Corii Colla by a smartphone camera can be achieved using this portable device. The unique architecture utilized in this device is ideal for a low-cost DNA analysis system.

A point-of-care rapid HIV-1 test using an isothermal recombinase-aided amplification and CRISPR Cas12a-mediated detection

Human immunodeficiency virus type one (HIV-1) infection is one of the major public health problems worldwide. Effective control of HIV-1 epidemic relies on early diagnosis of HIV-1 infection by using simple, rapid point-of-care test (POCT). An integrated assay was developed and evaluated in this study to combine a real-time isothermal reverse-transcription recombinase-aided amplification (rRT-RAA) and CRISPR Cas12a-mediated detection for HIV-1. The testing results could be directly observed with naked eye using a blue light imager, making it a suitable on-site testing assay. Our preliminary data indicated that the assay was capable of detecting 20 copies of purified HIV-1 DNA or RNA per reaction or as low as 123 copies/ml of HIV-1 viral load in clinical samples. When screening 155 clinical samples with or without HIV-1 infection, the sensitivity and specificity of the rRT-RAA assay were 98.95% (94/95) and 100% (60/60), respectively. The coefficient value was 0.986 when compared with the Chinese FDA approved HIV-1 RT-qPCR assay. Furthermore, the newly developed HIV-1 rRT-RAA assay could detect the major HIV-1 genotypes CRF01_AE, CRF07_BC, CRF08_BC, CRF08_BC and subtype B in China. Our preliminary results indicated that the rRT-RAA assay or its combination with CRISPR Cas12a-mediated detection could serve as a rapid, convenient, and robust assay for HIV-1 detection.

Electricity-free chemical heater for isothermal nucleic acid amplification with applications in COVID-19 home testing

Molecular detection of pathogenic nucleic acids from patient samples requires incubating biochemical reactions at specific temperatures to amplify DNA. This incubation is typically carried out with an electrical heater and a temperature controller. To reduce test cost, to eliminate the need for manufacturing incubators, which may require significant time, and to enable electricity-free operation, we use energetic compounds such as an Mg(Fe) alloy mixed with a phase-change material (PCM) that undergoes phase transformation at the desired incubation temperature. We dubbed this composite Energetic Phase Change Material (EPCM). When the EPCM is brought into contact with water, the magnesium alloy interacts with the water to produce heat. The EPCM heats up to its phase transition temperature. Any excess heat is absorbed as latent heat and the system is maintained at its desired incubation temperature, independent of ambient temperatures, long enough to facilitate enzymatic amplification. The EPCM together with colorimetric amplicon detection facilitates an inexpensive, disposable, point-of-need diagnostic test that does not require any electric power. We demonstrate the feasibility of our approach by detecting SARS-Cov-2 in saliva samples either without any instrumentation or with a palm-size CCD camera that enables us to follow the amplification process in real time.

SARS-CoV-2 in Mexico: Beyond Detection Methods, Scope and Limitations

The new coronavirus that was first identified in December 2019 in Wuhan China, now called SARS-CoV-2, which causes the disease called COVID-19, has spread from China to the entire world in a few months. Due to its contagious potential (R0: 5.7) and because there is still no effective treatment to stop the infection, and a vaccine for prevention it is not yet available to the general population, COVID-19 is currently considered a global health problem. The need to implement sensitive methods for the identification of individuals with COVID-19 has led to the development of different molecular and immunological tests. The importance of a timely and accurate diagnosis is essential to determine the course of the pandemic. The interpretation of the results obtained by each test as well as the factors that affect these results have not been fully described. In this review, we describe and analyze the different SARS-CoV-2 detection methods that have been performed in Mexico and are available worldwide, outlining their strengths and weaknesses. Further, a broader perspective of the correct use and interpretation of the results obtained with these diagnostic tools is proposed to improve the containment strategy and identify the true impact of the pandemic.

A critical review of point-of-care diagnostic technologies to combat viral pandemics

The COVID-19 global pandemic of 2019-2020 pointedly revealed the lack of diagnostic solutions that are able to keep pace with the rapid spread of the virus. Despite the promise of decades of lab-on-a-chip research, no commercial products were available to deliver rapid results or enable testing in the field at the onset of the pandemic. In this critical review, we assess the current state of progress on the development of point-of-care technologies for the diagnosis of viral diseases that cause pandemics. While many previous reviews have reported on progress in various lab-on-a-chip technologies, here we address the literature from the perspective of the testing needs of a rapidly expanding pandemic. First, we recommend a set of requirements to heed when designing point-of-care diagnostic technologies to address the testing needs of a pandemic. We then review the current state of assay technologies with a focus on isothermal amplification and lateral-flow immunoassays. Though there is much progress on assay development, we argue that the largest roadblock to deployment exists in sample preparation. We summarize current approaches to automate sample preparation and discuss both the progress and shortcomings of these developments. Finally, we provide our recommendations to the field of specific challenges to address in order to prepare for the next pandemic.

Simple Detection of Hepatitis B Virus in Using Loop-Mediated Isothermal Amplification Method

INTRODUCTION

US Military and civilian personnel regularly deploy to regions that are endemic for the Hepatitis B virus (HBV), including the Western Pacific, Africa, Eastern Mediterranean, Southeast Asia, and Europe. When patients have life-threatening injuries that require any blood component that is not immediately available, they are typically transfused with locally collected fresh whole blood from a walking blood bank. Currently, there is no simple and easy method for sensitively screening fresh blood in deployed theaters of conflict.

MATERIALS AND METHODS

In order to fill the gap, we have developed a loop-mediated isothermal amplification (LAMP) assay to detect the presence of HBV in blood products. The primers were designed to target the gene of the pre-Surface/Surface antigen region of HBV. The amplification reaction mixture was incubated at 60°C for 60 min. The amplicon can be detected by a handheld fluorescence tube scanner or an immune-chromatography test strip.

RESULTS

We were able to detect down to 10 copies of viral DNA by LAMP reaction for HBV DNA extracted from HBV-positive plasma. We also identified the optimal heat treatment condition (125°C for 10 min) for plasma specimens without requiring DNA extraction for the LAMP assay. The sensitivity of the assay was evaluated with polymerase chain reaction (PCR) confirmed HBV-positive samples. Using LAMP, we detected HBV in 107 out of 127 (84%) samples.

CONCLUSION

This LAMP assay has the potential to be used in resource-limited settings to improve the safety of locally collected blood in endemic regions.

Advances in HIV diagnosis and monitoring

Although highly active antiretroviral therapy (HAART) has been introduced over twenty years ago to treat Human Immunodeficiency Virus (HIV) positive patients, acquired immunodeficiency syndrome (AIDS) is still one of the deadliest diseases found worldwide. AIDS prevalence and mortality rates are usually more pronounced in resource-constrained countries than in the developed world. The lack of trained medical technicians, sophisticated diagnostic equipment, and the overall scarcity of medical infrastructures have severely impacted HIV/AIDS diagnostics, which hinders the initiation and periodic monitoring of antiretroviral therapy (ART). Currently, available HIV viral load assays are not well-suited for resource-limited settings due to their high cost and a requirement for medical/technical infrastructures. In this paper, we review current and emerging diagnostic assays for HIV detection, with a focus on point-of-care (POC) based immunoassays for viral load measurement, drug resistance, and HIV recurrence. We also discuss the limitations of the available HIV assays and highlight the technological advancements in cellphone, paper, and flexible material-based assays which have the potential to improve HIV diagnosis and monitoring, thus assisting with the management of the disease.

Development of a test kit for visual loop-mediated isothermal amplification of Salmonella in spiked ready-to-eat fruits and vegetables

The purpose of this study was to assemble two types of loop-mediated isothermal amplification (LAMP) kit that have the ability to visually detect Salmonella in ready-to-eat fruits and vegetables. The reaction results were obtained within 20-40 min after addition of DNA and can be discerned by the naked eye or an amplification plot. The stability of the LAMP wet kit was evident after multiple freezing and thawing cycles, and the one-step LAMP lyophilized kit was further evolved to allow ambient temperature transport for deployment in resource-limited settings. The cost-effective wet kit had the ability to detect minimum amounts of 1.8 CFU/ml Salmonella DNA without enrichment, while the sensitivity of the one-step LAMP lyophilized kit was only 9.8 × 10³ CFU/ml. They both have good anti-interference, as they were both able to detect 2.1 × 10² CFU/ml Salmonella mixed with 10⁶ CFU/ml four non-Salmonella strain mixture. Moreover, cucumber and lettuce that were contaminated with an initial inoculation of 1.7 CFU of Salmonella/10 g showed detection within a reaction time of 30 min after 10 h enrichment. The present research setup is a convenient and practical kit for Salmonella rapid detection that has good application prospects in food safety monitoring.

Inorganic Complexes and Metal-Based Nanomaterials for Infectious Disease Diagnostics

Infectious diseases claim millions of lives each year. Robust and accurate diagnostics are essential tools for identifying those who are at risk and in need of treatment in low-resource settings. Inorganic complexes and metal-based nanomaterials continue to drive the development of diagnostic platforms and strategies that enable infectious disease detection in low-resource settings. In this review, we highlight works from the past 20 years in which inorganic chemistry and nanotechnology were implemented in each of the core components that make up a diagnostic test. First, we present how inorganic biomarkers and their properties are leveraged for infectious disease detection. In the following section, we detail metal-based technologies that have been employed for sample preparation and biomarker isolation from sample matrices. We then describe how inorganic- and nanomaterial-based probes have been utilized in point-of-care diagnostics for signal generation. The following section discusses instrumentation for signal readout in resource-limited settings. Next, we highlight the detection of nucleic acids at the point of care as an emerging application of inorganic chemistry. Lastly, we consider the challenges that remain for translation of the aforementioned diagnostic platforms to low-resource settings.

A portable device for nucleic acid quantification powered by sunlight, a flame or electricity

A decentralized approach to diagnostics can decrease the time to treatment of infectious diseases in resource-limited settings. Yet most modern diagnostic tools require stable electricity and are not portable. Here, we describe a portable device for isothermal nucleic-acid quantification that can operate with power from electricity, sunlight or a flame, and that can store heat from intermittent energy sources, for operation when electrical power is not available or reliable. We deployed the device in two Ugandan health clinics, where it successfully operated through multiple power outages, with equivalent performance when powered via sunlight or electricity. A direct comparison between the portable device and commercial qPCR (quantitative polymerase chain reaction) machines for samples from 71 Ugandan patients (29 of which were tested in Uganda) for the presence of Kaposi’s sarcoma-associated herpesvirus DNA showed 94% agreement, with the four discordant samples having the lowest concentration of the herpesvirus DNA. The device’s flexibility in power supply provides a needed solution for on-field diagnostics.

A multiplexed RT-LAMP assay for detection of group M HIV-1 in plasma or whole blood

Isothermal nucleic acid amplification techniques, such as reverse-transcription loop-mediated isothermal amplification (RT-LAMP), exhibit characteristics that are suitable for the development of a rapid, low-cost NAT that can be used at the POC. For demonstration of utility for global use, studies are needed to validate the performance of RT-LAMP for the detection of divergent subtypes. In this study, we designed and evaluated multiplexed HIV-1 integrase RT-LAMP primers to detect subtypes within group M, along with an RNase P positive internal processing and amplification control. Using a panel of 26 viral isolates representing the major circulating subtypes, we demonstrated detection of all isolates of subtypes A1, C, D, F1, F2, G, CRF01_AE, CRF02_AG, and two unique recombinant forms (URFs). A whole blood panel created with one representative isolate of each subtype was successfully amplified with the group M HIV-1 integrase and RNase P internal control primers. The group M HIV-1 RT-LAMP assay was further evaluated on 61 plasma specimens obtained from persons from Cameroon and Uganda. The sequence-conserved group M HIV-1 RT-LAMP primers, coupled to a low-cost amplification device, may improve diagnosis of acute infection at the POC and provide timely confirmation of HIV status.

Evaluation of the stability of lyophilized loop-mediated isothermal amplification reagents for the detection of Coxiella burnetii

Coxiella burnetii, the causative pathogen for Q fever, is an obligate intracellular bacterium and designated as a biosafety level 3 agent. Detection and quantification of the bacteria with conventional culturing methods is time-consuming and poses significant health risks. Polymerase chain reaction (PCR)-based assays have been developed for detecting C. burnetii and could provide rapid diagnosis. However, they require specialized equipment, including a cold chain for PCR reagents that maintains their stability during storage and transport. These requirements limit the advantage of PCR-based methods, especially in resource-limited areas.

Previously, we had developed a lyophilized loop-mediated isothermal amplification (LAMP) assay to detect the presence of C. burnetii. To simplify and improve this assay, the reagents for the LAMP assay and the detecting reagent, SYBR green, were lyophilized together. The stability of the lyophilized reagents was evaluated by measuring changes in detection limit for plasmid DNA encoding a C. burnetii gene upon storage at 4 °C, 25 °C, or 37 °C. Our data indicate that the lyophilized reagents remain stable for 24 months when stored at 4 °C, 28 days at 25 °C, and 2 days at 37 °C. This improved LAMP assay can be easily performed in a simple water bath or heating block. The stability at ambient temperature, the simplicity of assay procedure, and the availability of low cost equipment make this method ideal for use in resource-limited settings where Q fever is endemic.