Rapid and sensitive detection of Vibrio harveyi by loop-mediated isothermal amplification combined with lateral flow dipstick targeted to vhhP2 gene

Vibrio harveyi is a causative agent of the Vibriosis or luminescent bacterial disease in worldwide aquaculture industry. A reliable assay for identification of V. harveyi infection is important to prevent the bacterial spread. In this study, biotinylated loop-mediated isothermal amplification (LAMP) amplicons were produced by a set of four designed primers that recognized specifically the V. harveyi vhhP2 gene, encoding a putative outer membrane protein with unknown function, followed by hybridization with an fluorescein isothiocyanate (FITC)-labelled probe and lateral flow dipstick (LFD) detection. A novel set of PCR primer was also designed specifically to vhhP2 gene and appear to be a species-specific tool for V. harveyi detection. The optimized time and temperature conditions for the LAMP assay were 90min at 65 degrees C. The LAMP-LFD and PCR methods accurately identified 22 isolates of V. harveyi but did not detect 16 non-harveyi Vibrio isolates, and 34 non-Vibrio bacterial isolates. The sensitivity of LAMP-LFD for V. harveyi detection in pure culture was 1.1x10(2)CFUmL(-1) or equivalent to 0.6CFU per reaction, while that of PCR was 6CFU per reaction. For spiked shrimp sample, the sensitivity of LAMP was 1.8x10(3)CFUg(-1) or equivalent to 5CFU per reaction, while that of PCR was 50CFU per reaction. In conclusion, the established LAMP-LFD methods provided a valuable tool for rapid identification of V. harveyi and can be used to distinguish V. harveyi from V. campbellii.