Isolation and Characterization of a Bacillus spp. Against Vibrio Parahaemolyticus from Shrimp Culture Ponds

Pathogenic Vibrio species is one of the major factors affecting the development of aquaculture and the safety of seafood. Using the antagonistic activity of probiotics against pathogens offers a promising alternative to fish and shrimp aquaculture. In the present study, nine strains of bacteria were isolated from the shrimp culture ponds and screened for their directly antimicrobial activity against pathogenic Vibrio parahaemolyticus Vp1. Strain G, showing significant antimicrobial and non-hemolytic activity, was selected for further assays. The results of biochemical and 16S rRNA sequence analysis indicated that strain G highly related to Bacillus licheniformis. The present study also evaluated the in vitro and in vivo antagonistic effect of strain G against the Vibrios. Strain G exhibited significant inhibitory activity of Vibrio fluvialis FX-2, Vibrio parahaemolyticus K, and V. parahaemolyticus Vp1 in vitro. The inhibition diameter of strain G against Vibrio spp. ranged from 16 to 20 mm on Nutrient Agar. Under in vivo conditions, strain G was non-toxic to zebrafish and effectively protected zebrafish against V. parahaemolyticus Vp1. The non-toxicity of strain G showed final survival rate of 100% in zebrafish at inoculation densities up to 5.6×1010 CFU/ml at 96 h postchallenge. A significant reduction in mortality (P<0.001) was found by addition of 1.5×108 CFU/ml or 1.5×107 CFU/ml strain G in zebrafish against V. parahaemolyticus Vp1. In conclusion, the present study result reveals that strain G is a promising probiotic candidate and has potential applications for controlling pathogenic Vibrios in aquaculture practices