Multilocus sequence analysis of Vibrionaceae isolated from farmed amberjack and the development of a multiplex PCR assay for the detection of pathogenic species

Since 2011, high mortality rates and symptoms consistent with vibriosis have been observed in farmed amberjack ( Seriola dumerili ) in Japan. To identify 41 strains isolated from diseased amberjack, a multilocus sequence analysis using nine concatenated genes ( ftsZ , gapA , gyrB , mreB , pyrH , recA , rpoA , topA and 16S rRNA) was conducted. Twenty‐seven strains were identified as Vibrio harveyi , suggesting an epidemic of V. harveyi infection in amberjack farms. Other strains were identified as Vibrio anguillarum , Vibrio owensii and Photobacterium damselae subsp. damselae . To develop an efficient diagnostic method for vibriosis in amberjack, a multiplex PCR system was developed to identify V. anguillarum , V. harveyi and P. damselae subsp. damselae . The method successfully discriminated between these three bacterial species, with amplification products of 350 bp for V. anguillarum , 545 bp for V. harveyi and 887 bp for P .  damselae subsp . damselae and can be used for diagnosis in aquaculture farms.