Rapid and Visible RPA-Cas12a fluorescence Assay for Accurate Detection of Zoonotic Dermatophytes

Background: Dermatophytosis is an infectious disease of global significance caused by several fungal species, which affects the hair, nails, or superficial layers of the skin. The most common zoonotic dermatophytes are Microsporum canis, Nannizzia gypsea and Trichophyton mentagrophytes. Wood9s lamp examination, microscopic identification and fungal culture are the main conventional diagnostic methods used in clinics. Less common methods are dermatophyte PCR and biopsy/histopathology. However, these methods also have limitations for providing both accuracy and timely on-site detection. The recent development of CRISPR-based diagnostic platform provides the possibility of a rapid, accurate, and portable diagnostic tool, which has huge potential for clinical applications. Objectives: The purpose of this study is to establish a molecular method for rapid and accurate diagnosis of clinical dermatophytes, which can accelerate clinical diagnostic testing and help timely treatment. Methods: In this paper, we design a Cas12a-based assay combined with recombinase polymerase amplification (RPA) to differentiate three main zoonotic dermatophytes. The limit of detection (LOD) is determined by using standard strains. A total of 25 clinical samples (hair and scurf) are identified to evaluate the sensitivity and specificity of this assay. Results: The RPA-Cas12a method showed high sensitivity and specificity (100% and 100%, respectively). The results could be observed directly by naked-eyes, and all tested samples were consistent with fungal culture and sequencing results. Conclusions: Compared with other methods, the RPA-Cas12a-fluorescence assay requires less time (30 minutes) and less complicated equipment, and visible changes can be clearly observed, which is suitable for on-site clinical diagnosis.