广东罗非鱼无乳链球菌分离鉴定及生物学特性分析OA北大核心CSTPCD

The purpose of this study was to investigate the current epidemic status and biological characteristics of Streptococcus agalactiae in tilapia and to provide new data for the prevention and control of S.agalactiae disease in fish.In this study,261 samples of diseased fish were collected from 2019 to 2020 from the main culture area of tilapia in Guangdong.The serotypes and four main virulence genes of the isolated strains were tested in PCR.The antibiotic sensitivity and multiple resistance to antibiotics of 31 kinds of antibiotics were detected.Total 35 S.agalactiae strains were isolated from 261 samples and determined to be serotype Ⅰa.The major virulence genes cylE,sodA and gapC were detected in all fish isolates and all tested human,bovine and fish reference strains while virulence gene scpB was only detected in human reference strains.The drug sensitivity testing showed that over 90％S.agalactiae isolates were susceptible to 19 antibiotics and the resistant genotypes and phenotypes of these isolates were partially consistent.The drug resistance rate of these isolates to 6 antibiotics was more than 50％.Furthermore,these 35 S.agalactiae strains were multidrug resistant,of which 77.1％(27/35)strains were resistant to more than 5 antibiotics.The pathogenicity testing showed that S.agalactiae isolates caused morbidity and death in zebrafish.In summary,this study investigated serotypes,virulence genes,drug resistance and pathogenicity of S.agalactiae isolates from tilapia,which provided a reference for the prevention and control of S.agalactiae disease of tilapia in Guangdong and even the whole country.