Studies on Pathogenicity, Genotype and Vaccine Efficacy of

• Main Author: 吳啟瑞
• Other Authors: 陳石柱
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/85884906897491437572

碩士 === 國立屏東科技大學 === 獸醫學系所 === 97 === Streptococcus inaie is a zoonotic pathogen and rare pathogen with a low virulence in human infection. In Taiwan, it causes serious infection tilapia and cobia, S. iniae were isolated from diseased tilapia, cobia, Managuense, and yellowfin seabream in sourthern Taiwan. Identification of all strains used in this study was confirmed by a PCR assay for S. iniae that gave the expected amplicon of 300 bp. In addition, their 16S rDNA sequences gave 100% sequence identity to S. iniae ( GenBank accession number AF048773 ).The phenotypic and genetic analysis results were present for by rapid ID 32 STREP and pulsed field gel eletrophrosis ( PFGE ), respectively. There were 10 phenotypes in S. iniae isolated from grey mullet and 11 phenotypes in Taiwan. S. iniae isolated from tilapia and cobia exhibited 4 genotypes and 3 genotypes by PFGE analysis using Apa I, respectively. However, S. iniae isolated from tilapia and cobia exhibited 5 genotypes and 4 genotypes by PFGE analysis using Sma I, respectively. Doxycycline was the most active antimicrobial agents against the isolates tested, followed by Amoxicillin, Erythromycin, and Florfenicol. For virulence test, the mean lethal dose of 3 strains ( SI 18, AOD 94451 and AOD 94453 ) of S. iniae ranged from 1.4 x107 to 3.4 x107 colony-forming units. Tilapia and cobia were inoculated intraperitioneally with formalin-killed whole cell bacterins and Freund complete adjuvant from 3 strains of S. iniae and follow by secondary IP injection after primary immunization. Peaked antibody titers in the serum of tilapia were observed at week 4 after secondary immunization and agglutinating titer of 1024 in tilapia were observed. The efficacy in protecting fish was evaluated in aquarium, fish were challenged with S. iniae strains ( SI 18, AOD 94451 and AOD 94453 ) at 4 weeks after second immunization. The fish injected with formalin-killed whole cell bacterins showed resistance against an artificial challenge with S. iniae. These results suggest that protective immune responses against S. iniae are induced in tilapia and cobia. In the aquarium challenge, the vaccine gave a relative percentage survival of 85.7%, and 87.5% after challenge with S. iniae in AOD 94451, and SI 18 vaccinated cobia group, respectively.