An immunochromatographic test strip for rapid detection of fish pathogen Edwardsiella tarda

Background: Edwardsiella tarda, the etiologic agent of edwardsiellosis, is a devastating fish pathogen prevailing in worldwide aquaculture industries and accounting for severe economic losses. There is a raising concern about E. tarda being a significant zoonotic pathogen, and it is urgent to develop a rapid detection of this pathogen. This is the first study to develop a test strip for rapid detection of E. tarda in turbot. Results: Mouse monoclonal antibodies (MAbs) and rabbit polyclonal antibody (PAb) against E. tarda were generated from immunization of mice and rabbits with a virulent isolate of E. tarda EIB202. Two MAbs specific to isolates of E. tarda were obtained, and one of them (25C1) was selected to conjugate with colloidal gold as the detector antibody. Rabbit PAb was used as the capture antibody. It was found the strip had no cross-reactivity with non-E. tarda bacterial microbes and the limit of detection (LOD) was 1 × 10 colony-forming units (CFU)/ml. The detection could be visually observed by the naked eye within 5 min. This test strip was verified with a similar detection limit and much less analysis time compared with a dot blot immunoassay (1 × 10 CFU/ml for LOD and 120 min for reaction time). When the samples were mixed with turbot tissue homogenates, strong immunoreactivity was observed over 10 CFU/ml, which suggested that the turbot tissue homogenates did not affect the detection of the strip. Pre-enrichment with homogenized turbot tissue for 12 h could increase the detection limit of the E. tarda present in the sample up to 1 to 10 CFU/ml. In practice, in detecting 20 turbot ascite samples infected by E. tarda, the immunochromatographic test strip showed a high accuracy (100% positive). Conclusions: The immunochromatographic test strip offers great promise for a rapid, simple, and economical method of E. tarda on-site detection, and with different antibodies, it might be used to detect other aquatic pathogens.