Isolation and Selection of <i>Bacillus</i> Strains for Inhibiting <i>Kurthia gibsonii</i>: A Novel Approach to Managing Hemorrhagic Disease in Pangasius (<i>Pangasianodon Hypopthalamus</i>)

Hemorrhagic disease in Pangasius ( Pangasianodon hypophthalmus ) poses a significant challenge to intensive aquaculture, leading to economic losses and reduced productivity. This study aimed to identify pathogenic bacteria associated with the disease and select beneficial bacterial strains with strong antagonistic potential for sustainable disease management. Through isolation and characterization, Kurthia gibsonii was identified as a novel pathogen causing hemorrhagic disease in pangasius, confirmed using infection experiments and MALDI-TOF mass spectrometry. Additionally, 14 bacterial strains were isolated from sediment and fish gut samples, of which eight exhibited inhibitory activity against K. gibsonii . Among these, two strains, Bacillus velezensis (A2A) and Bacillus subtilis (CL2.1), demonstrated the highest inhibitory effects, with inhibition zone diameters of 10.8 mm and 10.5 mm, respectively. These strains were identified through MALDI-TOF analysis and comparison with the NCBI database. The findings highlight the potential of Bacillus velezensis and Bacillus subtilis as biocontrol agents in mitigating hemorrhagic disease in pangasius, offering a sustainable alternative to antibiotics.