An extraction-free and one-pot two-temperature CRISPR/Cas12b system for visual detection of Group B Streptococcus by integrating with RPA.

Abstract

Group B Streptococcus (GBS) is a major cause of neonatal infections, and rapid detection is essential for timely clinical intervention. In this study, we developed an extraction-free, one-pot CRISPR/Cas12b assay for visual detection of GBS by combining with isothermal amplification, including loop-mediated isothermal amplification (LAMP) and recombinase polymerase amplification (RPA). The results showed that LAMP-CRISPR/Cas12b outperformed RPA-CRISPR/Cas12b system across all template concentrations, especially in low-copy template (30 and 10 copies/test) detection. To enhance the detection performance of RPA-CRISPR/Cas12b, we introduced a two-temperature protocol, with RPA reaction at 39°C followed by Cas12b activation at 62°C. Through the two-temperature approach, the detection rate of RPA-CRISPR/Cas12b system was significantly improved even in low-copy samples, achieving a sensitivity of 10 copies/test (1 copy/μL). Clinical validation using 60 vaginal-rectal swab samples showed 96.7% and 98.3% of concordance when compared to culture and qPCR methods, respectively. This assay offers a rapid (<1 h), highly sensitive, and user-friendly solution without requiring nucleic acid extraction or sophisticated instruments. Its compatibility with visual signal detection makes it ideal for point-of-care testing, especially in low-resource or time-sensitive settings. The platform can be adapted for broader pathogen detection in future field diagnostics.

Importance: This study presents a rapid, convenient, and highly accurate method for Group B Streptococcus (GBS) detection by integrating the CRISPR/Cas12b system with recombinase polymerase amplification, an isothermal nucleic acid amplification technique. To streamline the workflow, we established a one-pot, extraction-free assay that significantly reduces the detection time. Through the systematic optimization of the dual-temperature conditions, we enhanced the amplification efficiency of target DNA, thereby improving the sensitivity of the CRISPR/Cas12b system. Additionally, the incorporation of a UV-visible detection system enables visual readout, facilitating instrument-free testing suitable for point-of-care (POC) applications.