Administration of probiotic Bacillus licheniformis induces growth, immune and antioxidant enzyme activities, gut microbiota assembly and resistance to Vibrio parahaemolyticus in Litopenaeus vannamei

This study aimed to elucidate the effects of dietary Bacillus licheniformis ATCC 11946 (BL) on the growth, immune and antioxidant activities, intestinal morphology and microbiota, and susceptibility to Vibrio parahaemolyticus (VPAHPND) in juvenile pacific white shrimp, Litopenaeus vannamei (LV). Juvenile LV (initial weight = 0.63 +/- 0.001) were fed diets containing varying BL concentrations (0 (BL0), 10(6) (BL1), 10(7) (BL2) and 10(8) (BL3) CFU/g feed) for 8 weeks. Growth performance, immune and antioxidant enzyme activities, and intestinal morphology significantly improved in the probiotic-treated groups than the untreated. Regardless of the treatment group, the two dominant phyla were Proteobacteria and Bacteroidetes, whereas the two dominant genera were Ruegeria and Vibrio. Increasing inclusion of probiotics in diets led to significant increase in beneficial bacterial genera (Ruegeria, and Pseudoalteromonas) and a significant decrease in some known opportunistic pathogens (Vibrio, Tenacibaculum, Photobacterium, Kangiella and Spongiimonas) with the BL3 group witnessing the best. A 7-day challenge study with VPAHPND showed significantly high protection in the probiotic-treated groups, with the BL3, BL2 and BL1 obtaining 51%, 34% and 22% relative percentage survival, respectively. In conclusion, BL at 10(8) CFU/g feed should be used to help in shrimp production since it attained the most significant improvement.