Probiotic effects of Bacillus spp. from Pacific white shrimp (Litopenaeus vannamei) on water quality and shrimp growth, immune responses, and resistance to Vibrio parahaemolyticus (AHPND strains).

Acute hepatopancreatic necrosis disease (AHPND), a serious disease caused by some Vibrio spp., impacts the Pacific white shrimp industry worldwide, especially in Thailand. To effectively overcome this problem, efficacious probiotic candidates were isolated from shrimp farms near coastal areas. The isolated Bacillus probiotics were screened for their ability to control pathogenic Vibrio spp. and various V. parahaemolyticus AHPND (VPAHPND) strains. Among the obtained probiotics, Bacillus subtilis AQAHBS001, which broadly inhibited various strains of VPAHPND, was evaluated on a laboratory scale in water-soluble and feed applications of viable probiotic. The water addition of 1 × 103-1 × 105 CFU/mL of this probiotic effectively reduced total ammonia but did not improve shrimp growth and resistance to VPAHPND. However, feed supplemented with the selected probiotic at 1 × 107 and 1 × 109 CFU/kg diet and provided to shrimp continuously for 5 weeks efficiently improved growth, as indicated by significant final weight gain, average daily growth, specific growth rates and feed conversion ratios. Additionally, this probiotic significantly elevated immune responses through phagocytic activity and clearance efficiency and enhanced the expression of the prophenoloxidase, lysozyme, and anti-lipopolysaccharide factor genes. Furthermore, B. subtilis AQAHBS001 obviously improved midgut characteristics by increasing microvilli and intestinal wall thickness. Finally, this probiotic evidently improved resistance to VPAHPND.