| This study characterizes Vibrio alginolyticus and its pathogenic mechanisms in silver sea bream (Sparus sarba), develops vaccines against vibriosis and elucidates the protective mechanisms offered by vaccines against vibriosis.; The isolates of V. alginolyticus from diseased juvenile silver sea bream were characterized morphologically, physiologically, biochemically and serologically, and the virulence to juvenile silver sea bream was confirmed by experimental challenge. Inoculation of V. alginolyticus into sea bream via the intramuscular, intraperitoneal, injury/immersion and simple immersion routes resulted in 14-day LD50 values of 4.85 × 104 cfu/fish, 5.01 × 105 cfu/fish, 3.16 × 106 cfu/ml and >2.5 × 108 cfu/ml respectively.; Kinetic changes in hematological and immunological parameters of silver sea bream in response to progressive vibriosis infection, induced by V. alginolyticus and its extracellular products, were also described. Irrespective of whether the infection was induced by either natural or experimental routes, the general trend of macrophage phagocytosis was significantly elevated at the early stages of infection but declined significantly as infection advanced.; Chronic use of antibiotics will lead to development of antibiotic resistance, and our results demonstrated that most of the local vibrio isolates exhibited multiple antibiotic resistance. However, plasmid profiles indicate that the resistance to most antibiotics in the present vibrio isolates is mainly chromosomal.; Application of protective vaccines is an effective means for controlling fish against vibriosis. A number of vaccine preparations including formalin-, phenol-, chloroform- and heat-killed whole-cell bacterins, and subcellular lipopoly saccharides (LPS) were evaluated for their protective efficacies in preventing vibriosis in cultured silver sea bream. Our results indicate that fish immunized with two injections of formalin-killed bacterins (RPS = 80) or LPS (RPS = 100), displayed the best protection against V. alginolyticus by significant stimulating both specific and non-specific immune responses.; The effects of different administration routes on the efficacy of fish vaccination were also investigated, and our results indicated that fish immunized with two intraperitoneal (i.p.) injections of formalin-killed bacterins exhibited the best protection against pathogenic V. alginolyticus, and the RPS values were 100 or 85 upon receiving the higher or lower bacterial dose, respectively. (Abstract shortened by UMI.)... |
