| 莫金凤,周萌,李国章,等.一株鹅-鱼养殖环境下罗非鱼无乳链球菌的分离鉴定及药物敏感性分析[J].广东农业科学,2024,(6-7):- |
| Isolation, identification and drug sensitivity testing of a strain of Streptococcus agalactiae in tilapia (Oreochromis niloticus) from goose-fish polyculture environment |
| 投稿时间：2024-02-22 修订日期：2024-03-07 |
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| Abstract: |
| 【Objective】In order to investigate the cause of the tilapia disease outbreak in the geese-fish polyculture system, the growth characteristics, pathogenicity and drug sensitivity of the bacteria responsible were analyzed. This study aims to provide valuable scientific data for further research and effective prevention and control measures against tilapia disease. 【Methods】 Bacteria were isolated from the organs of diseased tilapia and identified using vaious methods such as morphological observation, physiological and biochemical identification, and16S rRNA gene sequence analysis. The impact of temperature, salinity and pH on the growth of pathogenic bacteria were analyzed, and a growth curve for the strain was plotted. The pathogenicity of the bacterial strain was assessed by intraperitoneal injection and oral feeding of mixed materials. Additionally, the susceptibility of the strain to 26 different antimicrobial agents belonging to 11 classes was determined using the drug sensitive disk method. 【Results】The dominant strain SA20160722YJN was isolated and purified from the brain tissue of infected tilapia. Through various methods including morphological observation, physiological and biochemical identification, 16S rRNA gene sequence analysis, and artificial regression infection test, the strain was identified as Streptococcus agalactiae (S. agalactiae), the main pathogen causing tilapia disease. The growth retardation stage of SA20160722YJN was 0~5h, and its logarithmic stage was 5~12h. The optimal conditions for growth are found to be a temperature of 37 ℃, pH value of 7.0, and salinity of 5‰. In an artificial infection test by intrabitoneal injection, the strain SA20160722YJN showed high pathogenicity to tilapia at a temperature of (29±1) ℃, with a lethal concentration of 2.4×108 CFU/mL. The pathogenicity of the strain was found to be closely related to bacterial concentration and water temperature. Further, the SA20160722YJN strain displayed resistance to six drugs, including trimethopridine, gentamicin and neomycin. It showed moderate sensitivity to four drugs, including enrofloxacin, ciprofloxacin and amikacin. Additionally, it was found to be sensitive to 16 drugs such as doxycycline, flufenicol, rifampicin. 【Conclusion】 This study concludes that Streptococcus agalactiae is the primary pathogen responsible for the outbreak of tilapia disease in the polyculture environment of goose-fish. Furthermore, it is found and the pathogenicity of this pathogen is strongly influenced by the bacterial concentration and water temperature. |
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