A CRISPR/Cas12a-based DNAzyme visualization platform for rapid discrimination of Streptococcus suis serotype 2 versus...

Streptococcus suis is a major swine pathogen with serotypes 2 and 14 posing zoonotic risks. However, distinguishing serotypes 1/2 from 2 or 1 from 14 remains challenging due to high similarity in their capsule polysaccharide (CPS) loci. Here, we developed a rapid, equipment-free discriminating platform targeting a single nucleotide polymorphism (SNP) at position 483 of the cpsK gene (G in serotypes 2/14 vs. T/C in 1/2/1). The method integrates recombinase polymerase amplification (RPA) with CRISPR/Cas12a and a G-quadruplex-hemin DNAzyme visualization system. RPA enables isothermal amplification, while CRISPR/Cas12a ensures single-nucleotide specificity by cleaving target DNA. Subsequent DNAzyme catalysis converts colorimetric substrates, enabling naked-eye differentiation via distinct color changes (blue for serotypes 1/2/1 vs. colorless for 2/14). This approach achieved a sensitivity of 10¹-10² copies per reaction and demonstrated 100 % specificity across 29 S. suis serotypes and related strains. Compared to PCR-based or sequencing methods, our platform eliminates reliance on thermocyclers or fluorescence detectors, reducing costs and operational complexity. The entire workflow, completed within 70 min, offers a practical solution for point-of-care testing in resource-limited settings. By enabling rapid, accurate discrimination, this tool will become a complementary tool for resolving ambiguous serotypes and enhances outbreak management in swine populations and mitigates zoonotic transmission.