Development of quantitative RT-PCR targeting gyrB mRNA for Flavobacterium psychrophilum infecting chum salmon Oncorhynchus keta
2020
Misaka, N. (Mariculture Fisheries Research Institute, Hokkaido Research Organization, Muroran, Hokkaido (Japan)) | Hatakeyama, M. | Suzuki, K.
We developed reverse transcription quantitative real-time PCR (RT-qPCR) targeting Flavobacterium psychrophilum gyrB mRNA for rapid detection of live bacteria in chum salmon Oncorhynchus keta fry. The mRNA was detected at 6.0 × 10E1-6.0 × 10E9 copies/μl with high correlation (R**2 = 0.9998). In March 2008, a BCWD outbreak occurred among chum salmon fry in a salmon hatchery in Hokkaido, Japan. The daily mortality peaked in mid-late March and decreased in early April when cumulative mortality reached 2.3%. During the disease course, the culturable cells and gyrB mRNA in kidney tissue samples from moribund individuals were identified and quantified by culture and RT-qPCR, respectively. The prevalence and concentration of gyrB mRNA was 60% and 4.9 × 10E3 copies/mg on March 21, and 100% and 5.6 × 10E4 copies/mg on March 26, respectively. No gyrB mRNA was detected on March 31, whereas culture prevalence was 95%, 100%, and 40% on March 21, 26, and 31, respectively. These results suggest that the RT- qPCR assay provides rapid quantitative detection of live bacteria in chum salmon fry.
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