Development of a Colloidal Gold Immunochromatographic Strip for Specific Detection of Photobacterium damselae subsp....

Photobacterium damselae subsp. piscicida (Pdp) is characterised by high infectivity and mortality and wide distribution, resulting in substantial economic losses to the global aquaculture industry. Therefore, it is critical to develop a simple, rapid and accurate diagnostic method for Pdp detection. Herein, two Pdp-specific monoclonal antibodies (mAbs 1H7 and 6E6) were obtained, indirect enzyme-linked immunosorbent assay and immunofluorescence analysis confirmed that the mAbs specifically recognised the outer membrane of Pdp but could not recognise the other Gram-positive or Gram-negative bacteria, indicating good specificity. A colloidal gold immunochromatographic strip (CGICS) was developed here for Pdp detection by optimising the colloidal gold labeling and antibody coating conditions using 1H7 as a colloidal gold-labelled antibody and 6E6 as a coated antibody. The CGICS exhibited a detection limit of 1 × 10⁵ CFU/mL for Pdp and a detection time of 10 min. Cross-reaction analysis revealed that the CGICS could specifically detect different Pdp isolates without cross-reaction with the other bacterial species or the subspecies P. damselae subsp. damselae. Stability analysis revealed that the CGICS were stored in closed plastic packaging at 25°C and 4°C for more than 8 months. The CGICS retained their detection limit after 6 months at 4°C, and 4 months at 25°C. Using tissues from the experimentally challenged Lateolabrax maculatus, the CGICS and polymerase chain reaction revealed a 100% coincidence rate. These findings indicated that the established CGICS exhibits high specificity and sensitivity. It is rapid and simple for Pdp detection, making it a potential on-site tool for Pdp detection in fish aquaculture.