Identification and molecular typing of <Emphasis Type="Italic">Streptococcus agalactiae</Emphasis> isolated from pond-cultured tilapia in China |
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| Authors: | Xing Ye Jiong Li Maixin Lu Guocheng Deng Xiaoyan Jiang Yuanyuan Tian Yingchun Quan Qian Jian |
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| Institution: | (1) Pearl River Fishery Research Institute, CAFS, Guangzhou, 510380, China;(2) College of Fisheries and Life, Shanghai Ocean University, Shanghai, 201306, China |
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| Abstract: | Bacteria strains with strong virulence were isolated from pond-cultured tilapia in China. They were identified as Streptococcus agalactiae by biochemical assays, and confirmed by 16S ribosomal RNA (rRNA) and group B Streptococcus (GBS)-specific gene cfb analyses. Multiplex polymerase chain reaction (PCR) assay of the alpha C protein (ACP) gene and capsular polysaccharide antigen
(cps) gene was employed to identify their molecular serotype (MS). Amplification of the ACP gene produced a 400-bp C alpha protein
gene (bca) fragment, suggesting that these isolates belong to MS Ia, Ib or II; amplification of cps produced a 790-bp amplicon, indicating that they belong to MS Ia/III-3. An additional PCR based on nucleotide difference
in the cps H–I region of MS Ia and III further suggested that the isolates belong to serotype MS Ia. Moreover, multi-locus sequence
typing (MLST) indicated that these strains were of sequence type 7 (ST-7). These results showed that isolates from different
regions of China shared the same MS and ST. However, none of the isolated ST-7 GBS corresponded to the capsular serotype,
suggesting that these fish GBS possessed specific molecular characteristics not present in human or other animals. Data from
this study will facilitate the understanding of epidemiology and nosogenesis of tilapia GBS and the establishment of effective
disease prevention methods. |
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