Evaluation of bacillus strains as an alternative to antibiotics against vibrio strains and vibrio-associated acute hepatopancreatic necrosis disease (AHPND) in penaeus vannamei

Title : Evaluation of bacillus strains as an alternative to antibiotics against vibrio strains and vibrio-associated acute hepatopancreatic necrosis disease (AHPND) in penaeus vannamei

Abstract:

Acute hepatopancreatic necrosis disease (AHPND) is a bacterial disease caused by Vibrio spp. carrying toxin genes (pirA and pirB) located in a large plasmid (69 kb). The disease is responsible for causing 100% mortality in shrimp farms within a few days. Previously, Vibrio parahaemolyticus (V. parahaemolyticus) was believed to be the primary causative agent of AHPND, however, it has been reported that various Vibrio strains, including V. campbellii, V.owensii, and V. harveyi, are identified as pathogens associated with AHPND. Antibiotics have been extensively used to treat bacterial diseases in aquaculture for a long time, however, the excessive use of antibiotics and their wrong utilization such as misuse or overuse has led to antibiotic resistance, making the use of antibiotics less effective in treating bacterial infections. Therefore, there is a need for alternative treatments, such as probiotics, to control bacterial infections, particularly those caused by pathogenic Vibrio and AHPND. This study aims to evaluate of the antimicrobial activity of five Bacillus strains (B1, B3, B5, B7, and B8) isolated from seawater in Jeju, Korea, against 12 Vibrio strains including 10 AHPND strains and 2 non-AHPND strains. The dot-spot method was used to evaluate the inhibitory effects of Bacillus strains on Vibrio strains. All tested Bacillus strains inhibited the growth of at least one Vibrio strains. Among tested Bacillus strains, B1 and B3 were the most effective against the tested Vibrio strains, particularly against AHPND-causing V. campbellii (VcAHPND), and were used in a further shrimp challenge test. After immersing shrimp in VcAHPND for 48-60 h, a significantly higher survival rate was observed in the B1-treated group (100%) compared to non-Bacillus-treated group (64.3%). Quantitative PCR analysis of AHPND revealed that the cycle threshold values were 31.63 ± 0.2 (B1-treated group) and 38.04 ± 0.58 (B3-treated group), compared to 28.70 ± 0.42 in the non-Bacillus-treated group. Genome sequencing and phylogenetic analysis revealed that B1 and B3 were classified as B. velezensis. The 16S rRNA sequences and complete genome sequences of B1 and B3 were deposited in GenBank. In conclusion, this study suggests that Bacillus strains, particularly B1 and B3, could be used as an effective alternative to antibiotics for controlling Vibrio infections and AHPND in shrimp aquaculture. The use of probiotics in aquaculture is an eco-friendly approach that does not harm the environment or have any adverse effects on human health. Further studies are warranted to investigate the mechanisms underlying the inhibitory effects of Bacillus strains on Vibrio strains and their potential use in other aquatic organism species.

Biography:

Miss Jeon graduated Veterinary Medicine, Kyungpook National University, Daegu, Korea, as MS in 2022. She then After that, she is currently advancing to the same graduate school as a Ph.D. student. She is conducting major disease monitoring and diagnostic method development research in farmed shrimp. She has published 10 research articles in SCI(E) journals.
Dr. Han studied Veterinary medicine at Kyungpook National University, Korea and received her PhD degree in Aquatic animal medicine in 2013 at Seoul National University. After one-year postdoctoral fellowship at Medical College of Georgia, Augusta, GA, USA, and three years research associated at OIE Reference Laboratory for Crustacean Diseases at University of Arizona, USA. And she obtained the position of an Assistant Professor at the Kyungpook National University. She has published over 80 research articles in SCI(E) journals.