Research
| Title： | Construction of Streptococcus agalactiae sialic acid mutant and evaluation of its potential as a live attenuated vaccine in Nile tilapia (Oreochromis niloticus) |
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| First author： | Hao, Jingwen; Wang, Shuyi; Wei, Zhaohui; Zhang, Qianqian; Wu, Zhenbing; Lin, Yaoyao; Yang, Jicheng; Zhang, Jinyong; Zhang, Defeng; Li, Aihua |
| Journal： | JOURNAL OF APPLIED MICROBIOLOGY |
| Years： | 2022 |
| DOI： | 10.1111/jam.15706 |
| Abstract： | Aims This study aimed to develop a live attenuated vaccine as an effective approach to prevent streptococcosis in tilapia (Oreochromis niloticus). Methods and results We eliminated the virulence factor, sialic acid (Sia) encoded by the neuA-D gene cluster from the Group B Streptococcus (Streptococcus agalactiae, GBS) strain WC1535, to construct Sia-deficient S. agalactiae (Delta Sia) mutant by homologous recombination. Results showed that the Delta Sia mutant had higher adherence to HEp-2 cells and lower resistance to RAW264.7 cell phagocytosis than the wild-type S. agalactiae. The virulence of the Delta Sia mutant to tilapia dramatically decreased with no virulence recovery. The relative percent survivals (RPSs) were 50.00% and 54.50% at 30 days when challenged at the wild-type WC1535 doses of 1.0 x 10(7) and 5.0 x 10(7) CFU fish(-1), respectively, via intraperitoneal (IP) injection. The tilapia vaccinated via IP injection with the Delta Sia mutant induced strong antibody agglutination titers. The expression of IL-1 beta, TNF-alpha, MHC-I alpha, and MHC-II beta could be enhanced in the intestine, spleen, and head kidney for tilapia administered with the Delta Sia mutant. Conclusions GBS Sia plays a critical role in adherence to HEp-2 cells and resistance to the immune clearance of RAW264.7 cells. Moreover, the Delta Sia mutant is a safe, stable, and immunogenic live attenuated vaccine candidate to protect tilapia against GBS infection. Significance and impact of study The results offer more evidence of the importance of Sia in GBS and may be instructive in the control of tilapia streptococcosis. |
