Demonstration of residual antibacterial activity in plasma of vaccinated Penaeus vannamei

Abstract

Plasma from naı̈ve Penaeus vannamei juveniles lacked antibacterial factors and significantly enhanced the growth of Escherichia coli strain XL1-Blue MRF′ compared with sea water complex (SWC) nutrient medium. In contrast, plasma from prawns previously injected with both live, non pathogenic Vibrio harveyi strain DPEX and formalin-killed cells of V. harveyi strains BP04, DPEX, E. coli and sterile shrimp salt solution (SSS), inhibited bacterial growth. Antibacterial activity appeared within 6 h and was detectable until 7 days after “vaccine” administration. Lysozyme activity was not detected in plasma from vaccinated prawns. Both in vitro and in vivo bacterial killing were facilitated by vaccine administration. Activation of the prophenoloxidase (proPO) system was independent of bacterial virulence.