Development of a Lateral Flow Strip-Based Recombinase-Aided Amplification for Active <i>Streptococcus dysgalactiae</i> emerging in channel catfish ( <i>Ictalurus punctatus</i> )

Streptococcus dysgalactiae has become an important pathogen affecting mammals and fish (especially farmed fish). The development of a rapid, accurate, and sensitive diagnostic method will aid in the prevention of S. dysgalactiae infection. In this study, a method combining recombinase-aided amplification and a lateral flow dipstick (RAA-LFD) was developed to detect active S. dysgalactiae infection. The RAA-LFD detection was based on the ISP gene of S. dysgalactiae as the target, which could be accomplished with the lowest detection limit of 1.002×10 2 pg/μL reaction under optimal reaction conditions of 39 °C for 15 min. RAA-LFD and conventional PCR were used to detect 50 experimental samples invaded by S. dysgalactiae disease materials. The results showed that the positive concordance rate of the two methods was 97.6%, the negative concordance rate was 90.0%, and the total concordance rate was 98.0%. Compared with conventional PCR, the Area Under the ROC Curve (AUC) of RAA-LFD was 0.950, and the sensitivity and specificity were 100% and 90%, respectively. The RAA-LFD of S. dysgalactiae infection is convenient for rapid clinical detection.