| In decades, with the rapid development of tilapia aquaculture industry, thediseases of cultured fish took place frequently, especially the disease of Streptococcus,causing huge economic loss to aquaculture. In this study, we mainly focused on thegreat harm caused by Streptococcus agalactiae to the tilapia aquaculture industry inchina, developing a vaccine to prevent Streptococcosis of fish. Streptococcusagalactiae was isolated and identificated, culture conditions was optimizated and theefficacy of S.agalactiae vaccine in tilapia was evaluated.40strains of Streptococcus were isolated from the samples of sickness tilapia inGuang Dong and Guang Xi and Hai Nan. These strains were confirmed to beS.agalactiae after being identified by the methods of traditional and molecular biology.The pathogenicity was analyzed to the6strains S.agalactiae with regionalrepresentation in tilapia, and the difference of virulence was studied to the strainsfrom different regions. The strain with good immunogenicity was screened to thepreparation of vaccine. The result shows that the S.agalactiae isolated from ZhanJiang had stronger virulence, which was suitable for the preparation of vaccine.According to the characteristics of culture and growth in S.agalactiae, the effects ofdifferent factors on its growth, including initial pH and dissolved oxygen andtemperature and nutrition factor in the fluid culture medium were studied to optimizeits growth parameters. The results indicate that the initial pH7～8,28～37℃and the200rpm speed of oscillation were optimal for the S.agalactiae, the maximal bacteria’sconcentration could be achieved by supplying2mg/mL glucose and20mg/mL yeastpowder in the BHI.Our objective was to develop an application vaccine against S.agalactiae. Avaccine was prepared with formalin-inactivated strain ZJ02selected from clinicalisolates of S.agalactiae to study on immune protective effect and antibody titer.Tilapia was vaccinated by injection and bath, and tilapia was immunized by fourdifferent concentrations of white oil aduvent inactivated vaccine in injection group.The vaccine was using with three different adjuvents of Raceanisodamine、fatty alcohol polyoxyethylene ether and Sodium chloride in immersion group. The immuneeffect of vaccine was studied by detecting the antibody activities and lysozymeactivities and superoxide dismutase activities and catalase activities andmalondialdehyde in the serum from tilapia. The tilapia immunized with vaccineshowed stronger immunogenicity. Antibody titer in the serum was significantlyimproved compared to control group. The antibody of injection group and immersiongroup can reach1:256and1:128. Different concentrations of vaccine in injectiongroup received a higher protective rate, and high concentration of vaccine can reach96％. Vaccine with three adjuvants received59％、64％、55％in the immersiongroup. The antibody activities, lysozyme activities, superoxide dismutase activities,catalase activities and malondialdehyde in the serum showed significantly higher thanthose of the control group (p<0.05). Thus, our data suggest that the tilapia receives agood immune protection by S.agalactiae vaccine. The immunization dose hadsignificantly influence on immune efficacy of injection group. The relative rates ofprotection was improved by the increasing immunization dose. The vaccine received ahigher antibody titer and a better immune protective effect by aduvant. Different ofimmune aduvant had different immune protective rate on immune efficacy of bathgroup. Tilapia produced strong immunity by using S.agalactiae vaccine, and thevaccine is effective in protecting tilapia against bacterial disease caused byS.agalactiae. However, the preparation and application of S.agalactiae vaccine willbecome an important guarantee on the sustained and healthy development of tilapiaaquaculture. |
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