Demonstration of residual antibacterial activity in plasma of vaccinated Penaeus Õannamei

Plasma from naıve Penaeus Õannamei juveniles lacked antibacterial factors and significantly ̈ enhanced the growth of Escherichia coli strain XL1-Blue MRF compared with sea water Ž . complex SWC nutrient medium. In contrast, plasma from prawns previously injected with both live, non pathogenic Vibrio harÕeyi strain DPEX and formalin-killed cells of V. harÕeyi strains Ž . 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 Ž . proPO system was independent of bacterial virulence. q 2000 Elsevier Science B.V. All rights reserved.