Antibacterial Bacillus strains from the Mekong Delta: Combating Vibrio parahaemolyticus in intensive white-leg shrimp aquaculture

Vibrio parahaemolyticus is a major bacterial pathogen causing significant losses in the global shrimp farming industry, including in Vietnam. The overuse of antibiotics for controlling V. parahaemolyticus has led to increased bacterial resistance. This study aimed to isolate and screen indigenous Bacillus strains with inhibitory activity against V. parahaemolyticus, which causes Early Mortality Syndrome (EMS) or Acute Hepatopancreatic Necrosis Disease (AHPNS) in intensively farmed white-leg shrimp (Litopenaeus vannamei) in Bac Lieu province, Mekong Delta, Vietnam. A total of forty-two Bacillus strains were isolated from the intestines of healthy shrimp, pond mud, and pond water. The well diffusion agar method revealed that twenty out of the forty-two strains exhibited inhibitory effects against V. parahaemolyticus. Among these, four strains, identified as BLN7, STNC, BLB7, and BLN8, demonstrated the strongest antagonistic activity, with inhibition zone diameters of 24 ± 0.00, 12.03 ± 0.06, 11.97 ± 0.06, and 11.93 ± 0.12 mm, respectively. Additionally, the study found that these four strains possess extracellular enzyme activities, including amylase, cellulase, and protease. Molecular identification through 16S rRNA gene sequencing, along with morphological, physiological, and biochemical analysis, confirmed that strains BLN7 and STNC belong to Bacillus spp. These findings provide