Enhanced immune defences in Pacific white shrimp (Litopenaeus vannamei) post-exposure to a vibrio vaccine

This study was conducted to determine if exposure of shrimp, Litopenaeus vannamei, to a commercial anti-vibrio vaccine caused changes in antibacterial and cellular (phagocytosis) defences. Shrimp post-larvae were administered either Vibromax™ vaccine or a blank preparation. Whole body homogenates were prepared before (day 0), during (day 10) and after (day 20) vaccination and incubated with a selection of pathogenic vibrios. Homogenate from day 0 animals showed natural antibacterial activity towards Vibrioanguillarum which was significantly enhanced for bacteria-exposed shrimp at 10 days post-challenge. This effect of the vaccine was short-term in its duration. No antibacterial activity was observed in day 0 shrimp homogenate against Vibrio alginolyticus but it was significantly enhanced for both vaccinated and blank-vaccinated shrimp by day 10. No natural or inducible antibacterial activity was observed against Vibrio harveyi at 0, 10 or 20 days post-challenge. To determine if prior exposure of shrimp to inactivated vibrios results in elevated hemocyte phagocytic activity, juveniles were injected with either a mixture of formalin-inactivated vibrios or saline. Hemocyte monolayers made from these shrimp were overlaid with a 1:1 mix of Bacillus subtilis and these vibrios. Hemocytes from vibrio-exposed animals showed elevated levels of internalised vibrios compared with those from the saline injected group. These studies show selectively enhanced cellular defences of shrimp following 'vaccination'.