Effects of Bacillus subtilis E20 isolated from fermented soybean on immune parameters and the disease
resistance of the white shrimp (Litopenaeus vannamei) after 98 days of B. subtilis E20 feeding were
evaluated in this study. Shrimp fed B. subtilis E20-containing diets at concentrations of 106 (E206), 107
(E207), and 108 (E208) cfu kg1, respectively, had significantly increased survival rates of 13.3%, 16.7%,
and 20%, compared to the control (fed no probiotic) after being challenged with Vibrio alginolyticus. There
were no significant differences in the total hemocyte count, respiratory burst, or superoxide dismutase
glutathione peroxidase among all treatments. Shrimp fed a higher concentration of the probiotic (E208)
exhibited significant increases in phenoloxidase activity, phagocytic activity, and clearance efficiency
compared to control shrimp. In addition, B. subtilis E20 showed a weaker inhibitory effect against the
growth of Aeromona hydrophila with around a 0.3-cm inhibitory zone, but showed no inhibitory effects
against other selected pathogens, such as white shrimp pathogens: V. alginolyticus and Vibrio vulnificus.
These results suggest that the increased resistance of shrimp after B. subtilis E20 consumption occurs
through immune modifications, such as increases in phenoloxidase activity, phagocytic activity, and
clearance efficiency against V. alginolyticus.