Aims: The present study evaluated the in vitro and in vivo antagonistic effect of Bacillus against the pathogenic vibrios.
Methods and results: Cell-free extracts of Bacillus subtilis BT23 showed greater inhibitory effects against the growth of Vibrio harveyi isolated by agar antagonism assay from Penaeus monodon with black gill disease. The probiotic effect of Bacillus was tested by exposing shrimp to B. subtilis BT23 at a density of 106-108 cfu ml-1 for 6 d before a challenge with V. harveyi at 103-104 cfu ml-1 for 1 h infection. The combined results of long- and short-term probiotic treatment of B. subtilis BT23 showed a 90% reduction in accumulated mortality.
Conclusions: This study reports that pathogenic vibrios were controlled by Bacillus under in vitro and in vivo conditions.
Significance and impact of the study: Results indicated that probiotic treatment offers a promising alternative to the use of antibiotics in shrimp aquaculture.