Litopenaeus vannamei immunestimulated with Macrocystis pyrifera extract: improving the immune response against Vibrio campbellii

Objective: To examine the immune responses of Litopenaeus vannamei after different treatments with a hot water extract of Macrocystis pyrifera (M. pyrifera) and a subsequent challenge with Vibrio campbellii (V. campbellii). Methods: A total of 184 adult white shrimp that were infected with V. campbellii (1×10 6 CFU/ shrimp) were immunostimulate by the hot-water extract from M. pyrifera via either injection (10 µg) or immersion (350 mg/L), the experimental controls were injected with either saline solution or V. campbellii (1×10 6 CFU/shrimp). The bacterial DNA depuration rate, antimicrobial activity and total hemocyte count were evaluated in hemolymph samples at 2, 6, 12, 24, 48 and 72 h postinfection. Results: Injected shrimp (10 µg M. pyrifera extract) demonstrated the best clearance of bacterial infection, with 82% survival at 72 h post-infection (cellular response). Hemolymph from the immersed organisms had the best antimicrobial activity against Escherichia coli growth; specifically, the most efficient antimicrobial activity was observed at 24 h post-infection. Both types of immunostimulated shrimp had similar total hemocyte counts at 24 h post-infection (1.63- 1.59 million/mL); however, after 72 h, injected shrimp had higher total hemocyte counts than immersed animals (2.59 v.s. 0.56 million/mL). Conclusions: The injection of the M. pyrifera hot-water extract facilitated a more efficient response to V. campbellii infection due to the stimulation of the hemocytes of the shrimp. In other words, the cellular immune response was more efficient to eliminate bacterial infection than the humoral response in shrimp