Development of a Colourimetric Loop-Mediated Isothermal Amplification Assay for Rapid Detection of Streptococcus...

Streptococcus dysgalactiae is an emerging fish pathogen that causes streptococcosis, resulting in significant economic losses in aquaculture. Conventional detection methods, such as polymerase chain reaction assays, rely on sophisticated, expensive instrumentation, which limits their applicability in resource-limited or field settings. In this study, we developed a rapid, user-friendly and closed-tube colourimetric loop-mediated isothermal amplification (LAMP) assay for the detection of S. dysgalactiae. Six primers targeting the sagB gene were designed and assay conditions were optimised to enable visual detection. The LAMP assay produced results within 50 min and detected target bacteria at concentrations as low as 500 pg (1.195 × 10⁸ copies/reaction), with high specificity and no cross-reactivity observed against eight non-target bacterial species. Overall, this LAMP assay operates under isothermal conditions and provides clear visual readouts, offering a foundation for future field-based testing in aquaculture settings using fish and water samples.