Studies on Rickettsia-like Organism Infection in Cultured Tilapias in Taiwan

• Main Authors: HSIEH-CHIA YU, 謝嘉裕
• Other Authors: MING-CHEN TUNG
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/79605723971847232773

碩士 === 國立屏東科技大學 === 獸醫學系 === 88 === Since October 1992, the first outbreak of the disease caused by rickettsia-like organism（RLO）in cultured tilapias in Taiwan, there has been a great number of mortalities approximately 30 ~ 90% on the most cultured tilapias farms each year. In consequence of the major difficulty in the isolation and cultivation of the RLO, the research of the disease has made a little progress in the past. Therefore, the aim of this study was to establish the culturing methods and to develop the polymerase chain reaction（PCR）test for the detection of RLO. The RLO of tilapias was successfully to be cultivated in CHSE-214 cell line system, but was unable to be cultured in ten different synthetic media. The RLO was a gram-negative, intracellular parasite and frequently been observed within intracytoplasmic vacuoles of the host cell. The RLO was reisolated from the inoculated tilapia using the RLO infected CHSE-214 cells as an inoculum. According, the RLO isolated from the natually infected tilapia was confirmed by Koch's postulates. The bacterial 16S rDNA sequence was amplified directly from tissues of related fishes with RLO infection by polymerase chain reaction, first with broad-range primers（PTS-1 ＆ PTS-2）and then with specific primers（PTS-f ＆ PTS-r）. A unique 1304-base bacterial 16S rDNA sequence was amplified from spleen and kidney of all infected fishes. We then detected the sequence in tissue from all RLO infected fishes. The specificity of PCR was assessed with a panel of 17 bacterial strains（ATCC） and 9 strains of fish bacterial pathogens isolated and identified in our fish disease laboratory. Products derived from amplification were observed only from RLO, indicating that PCR technique can serve as a diagnostic tool for the detection of the RLO. Base on our results, we confirmed the fact that（1）this organism is existed in the environment, and（2）the RLO isolated and identified is a new species of gamma subdivision of Eubacteria infection in tilapias.