Recombinase-aided amplification-lateral flow dipstick assay-a specific and sensitive method for visual detection of avian infectious laryngotracheitis virus

Sex Identification of a Multispecies Carinatae Birds by Chicken EE0.6 Gene Using Real-Time Recombinase-Aid Amplification Assay

The difficulty in bird sex identification has made molecular sexing an important way to solve this problem. The conventional polymerase chain reaction (PCR) methods are time-consuming and dependent on laboratory equipment. Recombinase-aided amplification (RAA) is a rapid, specific, sensitive, and cost-effective isothermal nucleic acid amplification technique. Hence, a rapid birds sexing method based on real-time RAA targeting the unique conserved sequence 0.6-kb EcoRI fragment (EE0.6) gene of Carinatae birds has been established and showed good specificity at 39°C for 20 min. The limit of detection for the real-time RAA assay was determined to be 10 pg., which is 10 times more sensitive than the conventional PCR assay. For real clinical samples, the real-time RAA assay was successfully determined sex in a subset of nine bird species and was 100% consistent with the conventional PCR assay. Consequently, the present real-time RAA assay proves to be a powerful on-site detection tool that can be used for an efficient and reliable birds sexing for further studies on sex ratio and captive management.

Advances in Virus Detection Techniques Based on Recombinant Polymerase Amplification

Recombinase polymerase amplification (RPA) has emerged as a rapid, efficient, and highly sensitive method for nucleic acid amplification, thus becoming a focal point of research in the field of virus detection. This paper provides an overview of RPA, emphasizing its unique double-stranded DNA synthesis mechanism, rapid amplification efficiency, and capability to operate at room temperature, among other advantages. In addition, strategies and case studies of RPA in combination with other technologies are detailed to explore the advantages and potential of these integrated approaches for virus detection. Finally, the development prospect of RPA technology is prospected.

Duplex recombinase aided amplification-lateral flow dipstick assay for rapid distinction of Mycobacterium tuberculosis and Mycobacterium avium complex

Objectives

This study aims to develop a novel diagnostic approach using the recombinase aided amplification-lateral flow dipstick(RAA-LFD) assay for the distinction of Mycobacterium tuberculosis (MTB) and Mycobacterium avium complex (MAC), enabling rapid and convenient as well as accurate identification of them in clinical samples.

Methods

Our study established a duplex RAA-LFD assay capable of discriminating between MTB and MAC. Based on the principles of RAA primer and probe design, specific primers and probes were developed targeting the MTB IS6110 and the MAC DT1 separately. Optimization of reaction time points and temperatures was conducted, followed by an evaluation of specificity, sensitivity, and reproducibility. The established detection method was then applied to clinical samples and compared with smear microscopy, liquid culture, LAMP, and Xpert/MTB RIF in terms of diagnostic performance.

Results

The complete workflow allows for the effective amplification of the MTB IS6110 and MAC DT1 target sequences at constant 37°C within 20min, and the amplification products can be visually observed on the LFD test strip. This method exhibits high specificity, showing no cross-reactivity with nucleic acids from M. kansassi, M. abscessus, M. gordonae, M. chelonae, M. fortuitum, M. scrofulaceum, M. malmoense, M. chimaera, M. szulgai and common respiratory pathogens. It also demonstrates high sensitivity, with a detection limit as low as 102 CFU/mL. Additionally, the method's Coefficient of Variation (CV) is less than 5%, ensuring excellent repeatability and reliability. Furthermore, clinical performance evaluations, using Xpert/MTB RIF as the gold standard, demonstrated that the duplex RAA-LFD assay achieves a sensitivity of 92.86% and a specificity of 93.75%. It is also noteworthy that the assay exhibits considerable diagnostic efficacy in smear-negative patients.

Conclusions

Our study introduces a rapid, specific, and sensitive duplex RAA-LFD assay for the discriminatory diagnosis of MTB and MAC. This method represents a significant advancement in the field of infectious disease diagnostics, offering a valuable tool for rapid detection and management of MTB and MAC infections. The implementation of this approach in point-of-care settings could greatly enhance TB control and prevention efforts, especially in resource-limited environments.

Portable detection of Salmonella in food of animal origin via Cas12a-RAA combined with an LFS/PGM dual-signaling readout biosensor

A highly specific and sensitive rapid two-signal assay was developed for the detection of Salmonella typhimurium in foods of animal origin. The invA gene of Salmonella was used as the biorecognition element and recombinase-assisted amplification (RAA) technology for signal amplification. By utilizing the specific recognition and efficient trans-cleavage activity of CRISPR/Cas12a, point-of-care testing (POCT) for S. typhimurium was achieved via lateral flow strips (LFS) and personal glucometer (PGM) biosensors as dual signal readout systems, with sensitivities of 33 CFU/mL and 20 CFU/mL, respectively. Users can select the appropriate test system on the basis of specific application requirements: LFSs are ideal for rapid onsite screening, whereas glucometer biosensors offer precise quantitative determination. This approach simplifies the use of large instruments and overcomes site constraints, demonstrating good accuracy and applicability in animal-derived samples, with significant potential for the detection of other pathogens and for use in restricted environments.

Meat Authenticity Made Easy: DNA Extraction-Free Rapid Onsite Detection of Duck and Pork Ingredients in Beef and Lamb Using Dual-Recombinase-Aided Amplification and Multiplex Lateral Flow Strips

Meat adulteration is a major global concern that poses a threat to public health and consumer rights. However, current detection techniques, such as quantitative polymerase chain reaction (qPCR) and gas chromatography-mass spectrometry, are time-consuming and require sophisticated equipment. In this study, we developed a rapid onsite identification method for animal-derived ingredients by utilizing a fast nucleic acid lysis buffer to expedite the release of sample nucleic acids and combined it with dual-recombinase-aided amplification (dual-RAA) technology and visual multiplex lateral flow strips (MLFSs). Our method successfully detected duck- and bovine-derived, porcine- and bovine-derived, duck- and ovine-derived, and porcine- and ovine-derived meat in a rapid 20 min onsite detection assay, with a detection limit of 101 copies/50 μL reaction system for target genes. Moreover, our method accurately detected adulterated meat with proportions as low as 1:999. These findings have significant implications for food safety and the protection of consumer rights.

A Novel Sample-to-Answer Visual Nucleic Acid Detection System for Adenovirus Detection

Human adenoviruses (HAdVs) are common viruses that can cause local outbreaks in schools, communities and military camps, posing a huge threat to public health. An ideal POCT device for adenovirus detection in resource-limited settings is critical to control the spread of the virus. In this study, we developed an integrated and electricity-independent sample-to-answer system that can complete nucleic acid extraction, amplification, and detection at room temperature. This system is suitable for field and on-site detection because of its rapidity, sensitivity, lack of contamination, and lack of requirements of high-precision instruments and skilled technicians. It consists of two separate modules, ALP FINA (alkaline lysis with the paper-based filtration isolation of nucleic acid) and SV RPA (sealed and visual recombinase polymerase amplification). The extraction efficiency of ALP FINA can reach 48 to 84%, which is close to that of the conventional centrifuge column. The detection sensitivity of SV RPA is close to 10 copies/μL of AdvB and AdvE without aerosol contamination after repeated operations. When SV RPA was applied to the detection of nasopharyngeal swab samples of 19 patients who were infected with AdvB or AdvE as well as 10 healthy volunteers, its sensitivity and specificity reached 100%, respectively. IMPORTANCE HAdV infections are readily transmittable and, in some instances, highly contagious. Early and rapid diagnosis is essential for disease control. In this work, we developed a portable, disposable, and modularized sample-to-answer detection system for AdvB and AdvE, which rendered the entire test to be completely independent of electricity and other laboratory infrastructure. Thus, this detection system can be applied in resource-limited settings, and it has the potential to be further developed as an early diagnosis method in the field.

Effect of food matrix on rapid detection of Vibrio parahaemolyticus in aquatic products based on toxR gene

Vibrio parahaemolyticus has become an important public threat to human health. Rapid and robust pathogen diagnostics are necessary for monitoring its outbreak and spreading. Herein, we report an assay for the detection of V. parahaemolyticus based on recombinase aided amplification (RAA) combined with lateral flow dipstick (LFD), namely RAA-LFD. The RAA-LFD took 20 min at 36~38 ℃, and showed excellent specificity. It detected as low as 6.4 fg/µL of V. parahaemolyticus in genomic DNA, or 7.4 CFU/g spiked food samples with 4 h of enrichment. The limit of detection in shrimp (Litopenaeus Vannamei), fish (Carassius auratus), clam (Ruditapes philippinarum) evidenced that sensitivity was considerably affected by the food matrix. The presence of food matrix reduced the sensitivity of spiked food samples by 10 ~ 100 times. In the filed samples detection, RAA-LFD method showed good coincidence with GB4789.7-2013 method and PCR method at rates of 90.6% and 94.1%, respectively. RAA-LFD has high accuracy and sensitivity for the detection of V. parahaemolyticus, which can serve as a model tool to meet the growing need for point-of-care diagnosis of V. parahaemolyticus.

Rapid visual detection of anisakid nematodes using recombinase polymerase amplification and SYBR Green I

Anisakidosis is a food-borne parasitic disease (FBPD) caused by the third-stage larvae of the family Anisakidae. Therefore, it is important to develop a simple, rapid and equipment-free detection method for anisakids in fish samples or seafood since current methods are time-consuming and require complex instruments. In this study, a recombinase polymerase amplification (RPA)-based method was established for the first time to detect anisakids by targeting the internal transcribed spacer (ITS) regions. The detection results were visualized by including SYBR Green I (SG) in the method. The sensitivity of RPA-SG assay was 102 copies per reaction of recombinant plasmid (within 20 min at 37°C), similar to quantitative real-time PCR (qPCR). The assay had high specificity for detecting anisakids against other related parasites and host fish. In addition, the assay was further used to detect fresh marine fish contaminated with anisakids and it showed high precision. These results indicate that the novel RPA-SG assay suitable for visual detection of anisakids in the field and food safety control.

Rapid and Visual Detection of Type 2 Porcine Reproductive and Respiratory Syndrome Virus by Real-Time Fluorescence-Based Reverse Transcription Recombinase-Aided Amplification

Porcine reproductive and respiratory syndrome (PRRS) is one of the most important diseases that has brought significant economic losses to the swine industry worldwide. Rapid and accurate PRRS virus (PRRSV) detection is one of the key factors for PRRS prevention and control. This study developed a real-time fluorescence-based reverse transcription recombinase-aided amplification (RF-RT-RAA) method for type 2 PRRSV (PRRSV-2) detection. The RF-RT-RAA assay could be performed at 42 °C for 20 min with the optimal primers and a probe. RF-RT-RAA results could be monitored using real-time fluorescence read-out or visually observed with the naked eye using a portable blue light transilluminator. The method had a strong specificity; no cross-reaction was identified with the detected common swine viruses. Moreover, the technique yielded high sensitivity with the lowest detection limit of 10¹ copies/μL and exhibited good repeatability and reproductively with the coefficients of variation (CV) less than 10%. Eighty-seven clinical samples were tested using RF-RT-RAA and a commercial PRRSV-2 RT-qPCR detection kit. The coincidence rate was 100% between RF-RT-RAA (real-time fluorescence read-out) and RT-qPCR, and 97.7% between RF-RT-RAA (visually observed) and RT-qPCR. The RF-RT-RAA assay provides a new method for rapid and visual detection of PRRSV-2.

Rapid detection of Burkholderia cepacia complex carrying the 16S rRNA gene in clinical specimens by recombinase-aided amplification

The Burkholderia cepacia complex (BCC) is a group of opportunistic pathogens, including Burkholderia cepacia, Burkholderia multivorans, Burkholderia vietnamiensis and Burkholderia ambifaria, which can cause severe respiratory tract infections and lead to high mortality rates among humans. The early diagnosis and effective treatment of BCC infection are therefore crucial. In this study, a novel and rapid recombinase-aided amplification (RAA) assay targeting the 16S rRNA gene was developed for BCC detection. The protocol for this RAA assay could be completed in 10 min at 39°C, with a sensitivity of 10 copies per reaction and no cross-reactivity with other pathogens. To characterize the effectiveness of the RAA assay, we further collected 269 clinical samples from patients with bacterial pneumonia. The sensitivity and specificity of the RAA assay were 100% and 98.5%, respectively. Seven BCC-infected patients were detected using the RAA assay, and three BCC strains were isolated from the 269 clinical samples. Our data showed that the prevalence of BCC infection was 2.60%, which is higher than the 1.40% reported in previous studies, suggesting that high sensitivity is vital to BCC detection. We also screened a patient with B. vietnamiensis infection using the RAA assay in clinic, allowing for appropriate treatment to be initiated rapidly. Together, these data indicate that the RAA assay targeting the 16S rRNA gene can be applied for the early and rapid detection of BCC pathogens in patients with an uncharacterized infection who are immunocompromised or have underlying diseases, thereby providing guidance for effective treatment.

Development of an isothermal recombinase-aided amplification assay for the rapid and visualized detection of Klebsiella pneumoniae

BACKGROUND

Klebsiella pneumoniae is a zoonotic opportunistic pathogen, leading to severe infections in dairy cows and humans. Efficient, on-site and accurate detection of K. pneumoniae is necessary to reduce the harm of cow mastitis and human infections. The objective of this study was to establish a recombinase-aided amplification (RAA) method combined with lateral flow dipstick (LFD) for rapid detection of K. pneumoniae.

RESULTS

The primer concentration, incubation temperature and incubation time of the RAA reaction were optimized. When the primer concentration was 100 nmol L^-1 , the strongest band could be obtained by incubation at 37 °C for 20 min. The RAA-LFD method had high specificity to K. pneumoniae and showed no cross-reaction with other pathogens. In addition, the detection limit of RAA-LFD for K. pneumoniae was 20 fg genomic DNA and 2.5 × 10²  CFU mL^-1 of bacteria in pure culture, which is 100 times higher than that of polymerase chain reaction (PCR) detection. Moreover, the RAA-LFD method can detect K. pneumoniae at initial concentrations as low as 2.5 CFU per 25 mL in artificially spiked milk samples after at least incubation for 6 h. Importantly, RAA-LFD had a high agreement with a test accuracy of 96.9%, compared with the biochemical identification method. Also, the detection accuracy of RAA-LFD was higher than that of the PCR assay (95.3%).

CONCLUSIONS

The results demonstrated that the RAA-LFD assay is an accurate, sensitive, simple and point-of-use detection method for K. pneumoniae, which could be used as a potential application in the research laboratory and for disease diagnosis. © 2021 Society of Chemical Industry.

A novel rapid visual detection assay for Toxoplasma gondii combining recombinase-aided amplification and lateral flow dipstick coupled with CRISPR-Cas13a fluorescence (RAA-Cas13a-LFD)

Toxoplasmosis, a parasitic disease resulting from Toxoplasma gondii infection, remains prevalent worldwide, and causes great harm to immunodepressed patients, pregnant women and newborns. Although various molecular approaches to detect T. gondii infection are available, they are either costly or technically complex. This study aimed at developing a rapid visual detection assay using recombinase-aided amplification (RAA) and lateral flow dipstick (LFD) coupled with CRISPR-Cas13a fluorescence (RAA-Cas13a-LFD) to detect T. gondii. The RAA-Cas13a-LFD assay was performed in an incubator block at 37 °C within 2 h, and the amplification results were visualized and determined through LFD by the naked eye. The detection limit was 1 × 10^-6 ng/μL by our developed RAA-Cas13a-LFD protocol, 100-fold higher than that by qPCR assay (1 × 10^-8 ng/μL). No cross-reaction occurred either with the DNA of human blood or Ascaris lumbricoides, Digramma interrupta, Entamoeba coli, Fasciola gigantica, Plasmodium vivax, Schistosoma japonicum, Taenia solium, and Trichinella spiralis, and the positive rate by RAA-Cas13a-LFD assay was identical to that by qPCR assay (1.50% vs. 1.50%) in detecting T. gondii infection in the unknown blood samples obtained from clinical settings. Our findings demonstrate that this RAA-Cas13a-LFD assay is not only rapid, sensitive, and specific and allows direct visualization by the naked eye, but also eliminates sophisticated and costly equipment. More importantly, this technique can be applied to on-site surveillance of T. gondii.

Development of Recombinase Aided Amplification Combined With Disposable Nucleic Acid Test Strip for Rapid Detection of Porcine Circovirus Type 2

Porcine circovirus type 2 (PCV2) is the dominant causative agent of PCV2 systemic disease (PCV2-SD) in pigs. It can also associate with other diseases such as respiratory and enteric diseases, reproductive failure, porcine dermatitis and nephropathy syndrome in pigs. Currently, PCV2 infection is a considerable threat in the swine industry. Therefore, it is of great significance to prevent, control, and accurately detect PCV2 in pig farms. Recombinase aided amplification (RAA) technology is an isothermal nucleic acid amplification technology that could rapidly amplify the target gene fragment at a constant temperature. The amplification products labeled with specific molecules could be visually detected using the test strip with the corresponding antibody. In the present study, the RAA technology combined with a nucleic acid test strip (RAA-strip) was established for simple and specific detection of PCV2. Primers and probes targeting the PCV2 ORF2 gene were designed according to the RAA technology principles. The PCV2 RAA-strip established in this study could detect as low as 10³ copies/μL of recombinant plasmids containing the PCV2 ORF2 gene fragment. The lowest detection limit about viral DNA and virus titers was 6.7 × 10^-6 ng/μL and 10 TCID50/mL, respectively. Furthermore, no cross-reaction with other porcine viruses occurred at 37°C and within 15 min. We used 42 clinical samples to assess the performance of our established method. The positive rate of clinical samples detected by PCV2 RAA-strip was 50.00%. This was similar to that detected by PCV2 PCR (45.24%). In conclusion, due to the advantages of strong specificity, high sensitivity, excellent reproducibility, and simple operation method, our PCV2 RAA-strip is suitable for the rapid clinical detection of PCV2 on-site.