Novel Probiotic Bacillus velezensis PED-003 as an Effective Biological Control Agent against Fish Pathogenic Bacteria

Abstract

The rapid expansion of aquaculture has been accompanied by an increased incidence of bacterial diseases, resulting in substantial economic losses and reduced productivity. The excessive use of antibiotics for disease control has contributed to the emergence of antimicrobial resistance, environmental contamination, and residual toxicity in aquatic products. Therefore, the identification of effective probiotic bacteria with antimicrobial properties has become an important strategy for sustainable aquaculture. The present study evaluated the antibacterial activity of Bacillus velezensis PED-003 against selected fish pathogenic bacteria, including Aeromonas hydrophila, Vibrio parahaemolyticus, Pseudomonas aeruginosa, Edwardsiella tarda, Streptococcus iniae, and Staphylococcus aureus. Antibacterial efficacy was assessed using agar well diffusion, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) assays.

The results demonstrated that B. velezensis PED-003 exhibited broad-spectrum antibacterial activity against all tested pathogens. The highest inhibition zone was recorded against A. hydrophila (22.4 ± 0.5 mm), followed by S. aureus (20.3 ± 0.6 mm), V. parahaemolyticus (19.8 ± 0.4 mm), and S. iniae (18.7 ± 0.4 mm). Lower but significant inhibition was observed against P. aeruginosa (17.6 ± 0.3 mm) and E. tarda (15.9 ± 0.5 mm). MIC analysis revealed the strongest inhibitory activity against A. hydrophila and S. aureus, with complete growth inhibition at 1.25 mg/ml. Similarly, the lowest MBC values (2.50 mg/ml) were recorded for these pathogens, indicating potent bactericidal activity. The close relationship between MIC and MBC values suggested that the antimicrobial metabolites produced by B. velezensis PED-003 exerted both inhibitory and lethal effects on bacterial pathogens.

The strong antagonistic activity observed in this study may be attributed to the production of bioactive compounds such as bacteriocins, lipopeptides, antimicrobial peptides, and other extracellular metabolites. These findings demonstrate the potential of Bacillus velezensis PED-003 as an effective probiotic and biological control agent for disease prevention in aquaculture. The application of this strain may reduce dependence on antibiotics and contribute to sustainable fish health management. Further investigations involving metabolite characterization and in vivo challenge studies are recommended to validate its commercial application in aquaculture systems.