A field-deployable colorimetric loop-mediated isothermal amplification assay for the point-of-care diagnosis of the mariculture pathogen Photobacterium damselae subsp. damselae

Photobacterium damselae subsp. damselae (PDD) is a ubiquitous marine pathogen responsible for devastating epizootics in global aquaculture, demanding rapid, point-of-care diagnostic interventions. However, the reliance on sophisticated laboratory infrastructure for nucleic acid purification remains a critical logistical bottleneck. To address this limitation, we engineered a robust field-deployable loop-mediated isothermal amplification (LAMP) assay targeting the PDD-specific ureC locus. Through iterative calibration of stoichiometric and physicochemical parameters, the optimal reaction profile was formulated at 57°C for 55 min, utilizing 1.0 µL of Bst polymerase and an 8:1 inner-to-outer primer ratio. Rigorous analytical validation confirmed that the method exhibited taxonomic exclusivity for PDD, with no cross-reactivity against sympatric marine microbes. Furthermore, the system attained a low limit of detection of merely 13 plasmid copies, outperforming conventional PCR sensitivity by two orders of magnitude. Crucially, we seamlessly integrated this isothermal module with a simplified crude DNA extraction protocol. This streamlined pipeline enabled the intuitive colorimetric detection of PDD in the visceral tissues of experimentally challenged Sebastes schlegelii , completely circumventing the prerequisite for upstream DNA isolation. In conclusion, this ureC -anchored LAMP platform delivers a highly sensitive, specific, and macroscopically interpretable diagnostic modality, providing a practical alternative for the on-site epidemiological surveillance of PDD in resource-limited aquaculture environments.