The use of probiotics in aquaculture as a viable alternative has paved the way to ensure continuous sustainability in aquaculture. This study concentrated on evaluating the properties of Bacillus amyloliquefaciens isolated from the blue swimming crab (Portunus pelagicus) as a potential probiotic. This strain was used to develop multi-strain probiotics (MSP) incorporated feed for red hybrid tilapia as disease control and growth-promoting tool. Bacillus amyloliquefaciens is combined with two other probiotic strains from the genera of Lysinibacillus and Enterococcus to create MSP. The inhibitory zone displayed by MSP against Aeromonas hydrophila (13.0± 0.6 mm) and Streptococcus agalactiae (15.3± 0.8mm) was significantly higher than the single probiotic. When A. hydrophila was co-cultured with MSP at a concentration of 108 CFU mL-1, no growth of A. hydrophila was observed, indicating that the pathogen was completely inhibited. Furthermore, B. amyloliquefaciens also demonstrated antimicrobial activity against Vibrio parahaemolyticus in spot and well diffusion assays with significant inhibition zones of 5.3 ± 0.01mm and 4.4 ± 0.06 mm respectively. In a co-culture assay, this strain at a concentration of 106 CFU mL-1 showed a significant reduction of V. parahaemolyticus after 12 hours of incubation compared to the control group. In in vivo study, this strain significantly improved the survival rate (88%) of white shrimp, Litopeneaus vannamei compared to the control group with no probiotic added (43%). Biofilm can be considered as a good source of inorganic nutrients for promoting the growth and immunity of the cultured organism. The ability of B. amyloliquefaciens to form biofilm was tested and the highest biofilm formation was observed at 24hr, with an optical density of 3.67 mm. Thus, B. amyloliquefaciens can be considered to have a high potential for use in aquaculture industries. It has been demonstrated that this strain has excellent properties in terms of pathogen antagonism, biofilm formation, and host survival rate.
Keywords: Probiotic, Bacillus amyloliquefaciens, aquaculture, antagonism, survival, biofilm