Establishment of One-Pot ERA-CRISPR/Cas12a-Based Rapid Visual Assays and a TaqMan Quantitative PCR Assay for...

Lactococcus garvieae is a major bacterial pathogen responsible for lactococcosis outbreaks in aquaculture, resulting in substantial economic losses worldwide. Accurate identification of L. garvieae remains challenging because of its genetic similarity to other Lactococcus species and the limited field applicability of many existing molecular diagnostic methods. Therefore, there is an urgent need for a rapid, highly specific, and field-deployable analytical method that enables accurate identification of L. garvieae outside conventional laboratory settings. In this study, a one-pot analytical strategy integrating enzymatic recombinase amplification (ERA) with CRISPR/Cas12a detection was developed, enabling fluorescence or lateral flow dipstick (LFD) readouts within a single closed reaction tube. The one-pot ERA-CRISPR/Cas12a assays achieved a detection limit of 10 copies/reaction. When combined with a rapid DNA release protocol, qualitative detection could be completed within 50 min without the need for sophisticated instrumentation. In parallel, a TaqMan quantitative PCR assay was established as an analytical benchmark, exhibiting a detection limit of 20 copies/reaction with high linearity and good reproducibility. Clinical evaluation using 136 diseased fish samples demonstrated full concordance between the one-pot ERA-CRISPR/Cas12a and qPCR assays, with both methods achieving a positive detection rate of 23.5% (32/136). In addition, the ERA-CRISPR/Cas12a platform was successfully validated under simulated field conditions using a portable reaction device. This study presents a rapid and field-deployable CRISPR-based platform for the early detection and epidemiological surveillance of lactococcosis.