Synergistic Effects of Shewanella algae A3 and Serratia marcescens Van80 UB3 on Immune Response, Gene Expression and Resistance to Vibrio parahaemolyticus Vp5 in Pacific White Shrimp.

This study addresses the infection caused by Vibrio parahaemolyticus Vp5, which carries the pirA and pirB toxin genes responsible for hepatopancreatic necrosis disease (AHPND) in Pacific white shrimp, leading to significant production losses. The use of a host-associated probiotic is considered a promising strategy to prevent such diseases. In this laboratory experiment, the effect of indigenous probiotics Shewanella algae A3 and Serratia marcescens Van80 UB3 was evaluated in terms of histopathology, immunity, gene expression and their protective ability against AHPND-causing bacteria in Pacific white shrimp (2 ± 0.5 g) over a 30-day feeding trial. A total of 150 shrimp of post larvae-10 (PL-10) were divided into five treatment groups: probiotic A (S. algae A3) at 10 cfu/g, probiotic B (S. marcescens Van80 UB3) at the same dose, probiotic C (a 1:1 mixture of both strains), a positive control K (+) (standard feed with infection) and negative control K (-) (standard feed without infection). After a 30-day feeding, the shrimp were challenged with V. parahaemolyticus Vp5 and survival was recorded for 14 days. The result showed that shrimp treated with the mixed probiotic (group C) had the highest survival (95.83% ± 1.44%), which was significantly higher than the positive control (72.22% ± 1.57%) (p < 0.05). Furthermore, the expression of immune-related genes such as proPO and serine protease in the intestine, muscle and hepatopancreas was significantly increased in the mixed probiotic group compared to the other treatments. In contrast, the expression of the cathepsin L gene, associated with muscle growth, was significantly lower in this group (p < 0.05). Immune response parameters after a 14-day challenge were higher in the mixed probiotic group. Histological observations revealed that the intestine and hepatopancreas tissues in probiotic-treated shrimp were in better and more normal condition compared to the positive control. Overall, the findings suggest that supplementing shrimp diets with a combination of S. algae A3 and S. marcescens Van80 UB3 at 10 cfu/g of feed is effective in improving shrimp health and resistance to AHPND.