Haemolytic Bacillus subtilis, a potential pathogen of hemorrhage disease in farmed yellow catfish Pelteobagrus fulvidraco

The hemorrhagic disease has become a major bottleneck in yellow catfish Pelteobagrus fulvidraco aquaculture. Yet scarce information is available on Bacillus subtilis as a pathogen of hemorrhagic disease in cultured yellow catfish. In this study, a virulent isolate, temporarily named HS5, was isolated from hemorrhagic disease-infected cultured yellow catfish, and was identified phenotypically and molecularly as B. subtilis. In addition, isolate HS5 showed an LD50 value of 5.20x106 CFU/ml in yellow catfish, exhibited beta-haemolytic activity, harbored the virulent entFM gene, and displayed high susceptibility to enrofloxacin and florfenicol in aquaculture use. To the best of our knowledge, this is the first report of B. subtilis as a pathogen of hemorrhagic disease in farmed yellow catfish.