Construction of an RAA-CRISPR detection platform for differentiation of Brucella abortus A19-∆VirB12 vaccine strain from wild-type strains.

Brucella abortus is a primary etiological agent of bovine brucellosis, a zoonosis posing significant threats to livestock industries and public health. The recently developed A19-∆VirB12 vaccine strain, which carries a deletion of the VirB12 gene, complicates serological differentiation from wild-type infections. This study aimed to establish a rapid, accurate, and economical detection strategy targeting the VirB12 gene to distinguish the A19-∆VirB12 vaccine strain from wild-type B. abortus. We developed a recombinase-aided amplification (RAA) coupled with CRISPR/Cas12a-based detection method. Following optimization, primer pair C and crRNA1 were selected as optimal components, with 150 nM each of Cas12a protein and crRNA identified as the ideal concentrations in a 50 μL reaction. The assay demonstrated high analytical specificity, showing no cross-reactivity with six non-target bacterial pathogens. Sensitivity analysis established a limit of detection of 102 copies per reaction. When evaluated on 52 clinical samples, the RAA-CRISPR assay detected two positive samples, outperforming conventional PCR which detected only one. Crucially, the method yielded no positive signal when challenged with the A19-∆VirB12 gene-deficient vaccine strain, while successfully detecting wild-type strains A19 and S2, confirming its discriminatory capability. The entire workflow, comprising RAA amplification (30 min) and CRISPR-mediated cleavage (20 min), can be completed within one hour, with results visualized via fluorescence or lateral flow strips. This study successfully establishes a rapid, sensitive, and specific diagnostic method for distinguishing the A19-∆VirB12 vaccine strain from wild-type B. abortus, offering a practical tool for field surveillance and eradication programs.