| Summary: | 碩士 === 國立屏東科技大學 === 水產養殖系所 === 95 === In order to realize the damage of P Photobacterium damselae subsp. piscicida on cage-farmed cobia, this study isolated the pure strains from the infected fish of cage culture farms of Penghu, Hengchun and Hsiao Liu Chio Island from July 2003 to March 2006 to investigate their pathogenicity and toxicity, drug resistance to antibiotics, growth performance of strains, and diverseness in API biochemical characteristics. In addition, the phylogenetic analysis was studied by comparing all the tested strains of genotype. Furthermore, the possible appearance of mutant strains was investigated by sampling in different sites and stage.
In the experiment of pathogenicity by intraperitoneal injection (IP) in juvenile cobia (30~50 g), the LD50 value ranged from 103~104. The lethal capacity among 5 tested strains was ranked by 1.2×103 CFU/g body weight in 94-PT-049 strain (isolated from Hsiao Liu Chio) > 1.4×103 CFU/g body
weight in 94-PH-021 strain (Penghu) > 7.6×103 CFU/g body weight in 95-PH-032 strain (Penghu) > 8.5×103 CFU/g body weight in 94-PT-045 strain (Hsiao Liu Chio) > 4.0×104 CFU/g body weight in 93-PT-09 strain (Hsiao Liu Chio). The strains of 93-PT-01 (Hsiao Liu Chio), 93-PT-02 (Hsiao Liu Chio), 94-PH-019 (Penghu) 93-PT-068 (Hengchun), and standard (BCRC-17065) were not lethal to cobia. In the sensitivity of antibiotic experiments, the Amoxicillin、Ampicillin and Flumequine were effective to inhibit all of the tested strains. In aspects of growth performance of tested stains, the 94-PT-045 strain isolated from Pingtung is the best (p<0.05) and standard strain is the lowest (p<0.05). Using analysis of the sequence of 16S rRNA and Multiplex PCR, a 100% similarity between sampling strains and standard strain was found. In conclusion, no subspecies of P. damselae subsp. piscicida in this study. The characteristics and pathogenicity of strains were performed variably from different sampling areas. The phylogenetic analysis was similar betaren isolated strains and standard strain of P. damselae subsp. piscicida.
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