Recombinase Polymerase Research Articles

An RPA-Based CRISPR/Cas12a Assay in Combination with a Lateral Flow Assay for the Rapid Detection of Shigella flexneri in Food Samples.

Among the pathogens that cause infectious diarrhea in China, Shigella is the most prominent. Shigellosis affects both adults and children, particularly those in developing nations, with nearly 190 million annual cases and a third resulting in fatalities. The recently emerged CRISPR/Cas system has also been increasingly applied for the detection of different biological targets. The lateral flow assay (LFA) has the advantages of short detection time, simple operation, high sensitivity, and low cost, and it provides an ideal platform for on-site detection. In this study, a recombinase polymerase amplification-CRISPR/Cas12a-LFA test for Shigella flexneri was constructed. The established method had good specificity and sensitivity, and the qualitative accuracy of 32 tested strains reached 100%. The detection limit of genomic DNA reached 8.3 copies/μL. With the advantages of high accuracy and portability, this diagnostic apparatus represents a novel method of identification and detection of Shigella flexneri, particularly in settings that lack complex laboratory infrastructure.

CRISPR-Cas12a-based nanoparticle biosensor for detection of pathogenic bacteria in food

Pathogenic bacterial contamination of food is a major challenge in food safety and public health management. To monitor pathogenic bacteria in food, a rapid, sensitive, and specific pathogen detection method is needed. CRISPR-Cas12a has been developed as a sensitive method for detecting pathogenic bacteria, but its output signal is fluorescent, which need equipment to detect. Here, the nanoparticle probe was designed to detect the activity of Cas12a and were able to visualize the assay results by observing the color change by naked eyes. The target sequences of pathogenic bacteria were amplified by recombinase polymerase, then recognized and bound by the crRNA and Cas12a complex. The activated Cas12a cleaved the linker-ssDNA connecting the nanoparticles, causing the nanoparticles to transition from aggregation to dispersion, and the color showed as purple. The sensitivity analysis showed that the limits of detection (LOD) reached 1 × 10°CFU/mL, 1 × 104 CFU/mL, 1 × 102 CFU/mL, 1 × 103 CFU/mL, 1 × 101 CFU/mL for Escherichia coli, Salmonella typhimurium, Vibrio parahaemolyticus, Staphylococcus aureus, and Listeria monocytogenes, which were all specific for five bacteria in the milk samples. Therefore, this method is a dependable, fast, sensitive and specific method, which make the CRIPSR-Cas12a detection method more useful in bacterial pathogenic detection.

Recombinase Polymerase and Loop-Mediated Isothermal Amplification in the DNA Diagnostics of Infectious Diseases

Recombinase Polymerase and Loop-Mediated Isothermal Amplification in the DNA Diagnostics of Infectious Diseases

A Critical Study on DNA Probes Attached to Microplate for CRISPR/Cas12 Trans-Cleavage Activity.

CRISPR/Cas12-based biosensors are emerging tools for diagnostics. However, their application of heterogeneous formats needs the efficient detection of Cas12 activity. We investigated DNA probes attached to the microplate surface and cleaved by Cas12a. Single-stranded (ss) DNA probes (19 variants) and combined probes with double-stranded (ds) and ssDNA parts (eight variants) were compared. The cleavage efficiency of dsDNA-probes demonstrated a bell-shaped dependence on their length, with a cleavage maximum of 50%. On the other hand, the cleavage efficiency of ssDNA probes increased monotonously, reaching 70%. The most effective ssDNA probes were integrated with fluorescein, antibodies, and peroxidase conjugates as reporters for fluorescent, lateral flow, and chemiluminescent detection. Long ssDNA probes (120-145 nt) proved the best for detecting Cas12a trans-activity for all of the tested variants. We proposed a test system for the detection of the nucleocapsid (N) gene of SARS-CoV-2 based on Cas12 and the ssDNA-probe attached to the microplate surface; its fluorescent limit of detection was 0.86 nM. Being united with pre-amplification using recombinase polymerase, the system reached a detection limit of 0.01 fM, thus confirming the effectiveness of the chosen ssDNA probe for Cas12-based biosensors.

Development of propidium monoazide–recombinase polymerase amplification (PMA-RPA) assay for rapid detection of Streptococcus pyogenes and Streptococcus agalactiae

Streptococcus pyogenes (Group A Streptococcus, GAS) and Streptococcus agalactiae (Group B Streptococcus, GBS) are common pathogens that threaten public health. In this study, a double recombinase polymerase (RPA) amplification assay was developed to rapidly detect these pathogens. Specificity tests revealed that the GAS and GBS strains were positive for speB and SIP genes, respectively. In clinical samples, the double assay performed similarly to the traditional biochemical method. The limits of detection were both ≤100 copies per reaction. In tests for simulant-contaminated samples, bacterial-culture media containing 103 CFU/mL original concentrations of S. pyogenes and S. agalactiae were positive in RPA assays after incubating for 4 h. Results can be obtained at 37 °C in 20 min. To determine whether propidium monoazide (PMA) can eliminate the influence of DNA extracted from dead cells, a bacterial suspension was treated with PMA before DNA extraction. Findings of RPA assay showed that DNA extracted from dead cells had no fluorescence signal. Therefore, the PMA-RPA assay is a promising technology for field tests and rapid point-of-care diagnosis.