Enzymatic recombinase amplification coupled with CRISPR-Cas12a for ultrasensitive, rapid, and specific Porcine circovirus 3 detection

Detection of Porcine Circovirus (PCV) Using CRISPR-Cas12a/13a Coupled with Isothermal Amplification

The impact of porcine circovirus (PCV) on the worldwide pig industry is profound, leading to notable economic losses. Early and prompt identification of PCV is essential in managing and controlling this disease effectively. A range of detection techniques for PCV have been developed and primarily divided into two categories focusing on nucleic acid or serum antibody identification. The methodologies encompass conventional polymerase chain reaction (PCR), real-time fluorescence quantitative PCR (qPCR), fluorescence in situ hybridization (FISH), loop-mediated isothermal amplification (LAMP), immunofluorescence assay (IFA), immunohistochemistry (IHC), and enzyme-linked immunosorbent assay (ELISA). Despite their efficacy, these techniques are often impeded by the necessity for substantial investment in equipment, specialized knowledge, and intricate procedural steps, which complicate their application in real-time field detections. To surmount these challenges, a sensitive, rapid, and specific PCV detection method using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas12a/13a coupled with isothermal amplification, such as enzymatic recombinase amplification (ERA), recombinase polymerase amplification (RPA), and loop-mediated isothermal amplification (LAMP), has been developed. This novel method has undergone meticulous optimization for detecting PCV types 2, 3, and 4, boasting a remarkable sensitivity to identify a single copy per microliter. The specificity of this technique is exemplary, with no observable interaction with other porcine viruses such as PEDV, PRRSV, PRV, and CSFV. Its reliability has been validated with clinical samples, where it produced a perfect alignment with qPCR findings, showcasing a 100% coincidence rate. The elegance of merging CRISPR-Cas technology with isothermal amplification assays lies in its on-site testing without the need for expensive tools or trained personnel, rendering it exceptionally suitable for on-site applications, especially in resource-constrained swine farming environments. This review assesses and compares the process and characteristics inherent in the utilization of ERA/LAMP/RPA-CRISPR-Cas12a/Cas13a methodologies for the detection of PCV, providing critical insights into their practicality and effectiveness.

ERA-CRISPR/Cas12a system: a rapid, highly sensitive and specific assay for Mycobacterium tuberculosis

Introduction

Mycobacterium tuberculosis, the causative agent of human tuberculosis, poses a significant threat to global public health and imposes a considerable burden on the economy. However, existing laboratory diagnostic methods for M. tuberculosis are time-consuming and have limited sensitivity levels.

Methods

The CRISPR/Cas system, commonly known as the "gene scissors", demonstrates remarkable specificity and efficient signal amplification capabilities. Enzymatic recombinase amplification (ERA) was utilized to rapidly amplify trace DNA fragments at a consistent temperature without relying on thermal cyclers. By integrating of CRISPR/Cas12a with ERA, we successfully developed an ERA-CRISPR/Cas12a detection system that enables rapid identification of M. tuberculosis.

Results

The sensitivity of the ERA-CRISPR/Cas12a fluorescence and lateral flow systems was 9 copies/μL and 90 copies/μL, respectively. Simultaneously, the detection system exhibited no cross-reactivity with various of respiratory pathogens and non-tuberculosis mycobacteria, demonstrating a specificity of 100%. The positive concordance rate between the ERA-CRISPR/Cas12a fluorescence system and commercial qPCR was 100% in 60 clinical samples. Meanwhile, the lateral flow system showed a positive concordance rate of 93.8% when compared to commercial qPCR. Both methods demonstrated a negative concordance rate of 100%, and the test results can be obtained in 50 min at the earliest.

Discussion

The ERA-CRISPR/Cas12a system offers a rapid, sensitive, and specific method that presents a novel approach to laboratory diagnosis of M. tuberculosis.

Development of recombinase amplification assays for the rapid detection of infectious myonecrosis virus

Infectious myonecrosis virus (IMNV) has affected shrimp farming in many countries, such as northeastern Brazil and southeast Asia, and poses a serious threat to the global shrimp industry. Reverse transcription enzymatic recombinant amplification technology (RT-ERA) is a rapid DNA amplification assay with high specificity in isothermal conditions and has been widely applied to the pathogen's detection. In this study, two novel ERA assays of IMNV, real-time RT-ERA and an RT-ERA combined with lateral flow dipsticks assay (RT-ERA-LFD), were developed and evaluated. The real-time RT-ERA assay could be carried out at 38-42 °C and had the highest end-point fluorescence value and the smallest Ct value at 41 °C. The brightness and width of the detection line were at a maximum at 39 °C and 30 min, and these conditions were selected in RT-ERA-LFD. Both real-time RT-ERA and RT-ERA-LFD produced positive results with IMNV standard plasmids only and showed no cross-reaction with Vibrio parahaemolyticus, which causes acute hepatopancreatic necrosis disease (VpAHPND); white spot syndrome virus (WSSV); infectious hypodermal and hematopoietic necrosis virus (IHHNV); or Ecytonucleospora hepatopenaei (EHP). Meanwhile, we compared the sensitivities of nested RT-PCR, real-time RT-PCR, real-time RT-ERA, and RT-ERA-LFD. The sensitivities of real-time RT-ERA and RT-ERA-LFD were both 101 copies/μL. The detection sensitivities of nested RT-PCR and real-time RT-PCR were 100 and 102 copies/μL, respectively. As a result, two ERA assays were determined to be specific, sensitive, and economical methods for the on-site diagnosis of IMNV infection, showing great potential for the control of IMNV infections.

Combination of nucleic acid amplification and CRISPR/Cas technology in pathogen detection

Major health events caused by pathogenic microorganisms are increasing, seriously jeopardizing human lives. Currently PCR and ITA are widely used for rapid testing in food, medicine, industry and agriculture. However, due to the non-specificity of the amplification process, researchers have proposed the combination of nucleic acid amplification technology with the novel technology CRISPR for detection, which improves the specificity and credibility of results. This paper summarizes the research progress of nucleic acid amplification technology in conjunction with CRISPR/Cas technology for the detection of pathogens, which provides a reference and theoretical basis for the subsequent application of nucleic acid amplification technology in the field of pathogen detection.

An isothermal enzymatic recombinase amplification (ERA) assay for rapid and accurate detection of Enterocytozoon hepatopenaei infection in shrimp

Enterocytozoon hepatopenaei (EHP) is a kind of microsporidian parasite belonging to fungi, and poses a serious threat to prawn farmers. Due to the lack of effective treatments for EHP, the establishment of a rapid and sensitive detection method would be beneficial to the control and prevention of this prawn parasitic disease. In this study, an isothermal enzymatic recombinase amplification (EHP-ERA) assay that could diagnose EHP within 20 min at 42 °C was developed and evaluated. The determined final concentrations of primers and probe in the reaction system were 400 nM and 120 nM, respectively. EHP-ERA was carried out within 13 min (24.31 ± 0.37 Ct) with a detection limit of 10 copies/μL. The results of specificity test showed that EHP-ERA had no cross-reactivity with white spot syndrome virus (WSSV), Vibrio parahaemolyticus strain causing acute hepatopancreatic necrosis disease (VpAHPND), and infectious hypodermal and hematopoietic necrosis virus (IHHNV) and specific pathogen free (SPF) shrimp. Using 32 clinical samples, the practical diagnostic results of EHP-ERA was consistent with nested PCR and real-time PCR (qPCR) under the premise of less time-consuming and simpler operation. In summary, we established a simple, rapid, and effective ERA assay for the detection of EHP, which had great potential to be widely used in both lab and practical usage.

Rapid and Easy-Read Porcine Circovirus Type 4 Detection with CRISPR-Cas13a-Based Lateral Flow Strip

First identified as a new circovirus in Hunan Province in China in 2019, porcine circovirus (PCV4) is now widely detected in other Chinese provinces and South Korea. In recent years, the virus has threatened pig health and operations in the pig industry. Hence, early PCV4 detection and regular surveillance are required to control the spread of infection and prevent collateral damage to the industry. Due to PCV4 being difficult to isolate in vitro, molecular detection methods, such as conventional PCR and real-time PCR, and serological assays are currently the main methods used for the detection of PCV4 infection. However, they are time-consuming, labor-intensive, and complex and require professional personnel. To facilitate rapid pen-side PCV4 diagnoses, we used clustered regularly interspaced short palindromic repeats (CRISPR) and Cas13a technology to develop a quick testing kit. Five recombinase-aided amplification (RPA) primer sets were designed based on the conserved PCV4-Cap gene nucleotide region, which were used to determine several key lateral flow strip (LFD) characteristics (sensitivity, specificity, and accuracy). The results showed that the RPA-Cas13a-LFD reaction could detect PCV4 within 1.5 h in genomic DNA harboring a minimum of a single copy. Furthermore, the assay showed good specificity and absence of cross-reactivity with PCV2, PCV3, or other porcine viruses. When we tested 15 clinical samples, a high accuracy was also recorded. Therefore, we successfully developed a detection assay that was simple, fast, accurate, and suitable for on-site PCV4 testing.

Ultrasensitive, Specific, and Rapid Detection of Mycoplasma pneumoniae Using the ERA/CRISPR–Cas12a Dual System

Mycoplasma pneumoniae can cause severe respiratory tract infections and extrapulmonary diseases, which pose a significant threat to the health of children. Diagnostic methods for M. pneumoniae include isolation and culture, antibody detection, fluorescence quantitative PCR, and so on, but there are various shortcomings in time, cost, convenience, and sensitivity. In this study, we developed a rapid, sensitive, specific, and economical method for the detection of M. pneumoniae, termed the ERA/CRISPR–Cas12a dual system. The system used the high specificity and collateral cleavage activity of the LbCas12a protein, combined with enzymatic recombination amplification (ERA) technology with strong amplification ability, allowing the results to be observed by a portable fluorometer or visualized by the naked eye with a dipstick, which could be obtained in approximately 30 min. The ERA/CRISPR–Cas12a fluorescence and dipstick system were able to detect M. pneumoniae at titers as low as 1 and 100 copies/μL, respectively. The specificity of the two interpretation methods was 100%, and no cross-reaction with other pathogens was observed. In the evaluation of 92 clinical samples, the positive predictive agreements of the ERA/CRISPR–Cas12a fluorescence and dipstick systems with qPCR detection were 100% and 92.86%, respectively. The negative predictive agreements of both methods were 100%. In conclusion, this study established a portable, rapid, low-cost, ultrasensitive, and specific method for the early and rapid diagnosis of M. pneumoniae to meet the needs of on-site rapid detection in primary health institutions.