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ARS Home » Southeast Area » Stoneville, Mississippi » Warmwater Aquaculture Research Unit » Research » Publications at this Location » Publication #389532
Research Project: Improving the Productivity and Quality of Catfish Aquaculture

Location: Warmwater Aquaculture Research Unit

Title: Development and efficacy of Streptococcus iniae live-attenuated vaccines in Nile tilapia, Oreochromis niloticus

Author
item HECKMAN, TAYLOR - University Of California
item SHAHIN, KHALID - University Of California
item HENDERSON, EILEEN - University Of California
item WRIGHT, ALONNA - University Of California
item Waldbieser, Geoffrey - Geoff
item GRIFFIN, MATTHEW - Mississippi State University
item SOTO, ESTEBAN - University Of California

Submitted to: Fish and Shellfish Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2021
Publication Date: 1/10/2022
Citation: Heckman, T.I., Shahin, K., Henderson, E.E., Wright, A., Waldbieser, G.C., Griffin, M.J., Soto, E. 2022. Development and efficacy of Streptococcus iniae live-attenuated vaccines in Nile tilapia, Oreochromis niloticus. Fish and Shellfish Immunology. 121:152-162. https://doi.org/10.1016/j.fsi.2021.12.043.
DOI: https://doi.org/10.1016/j.fsi.2021.12.043

Interpretive Summary: Streptococcus iniae is a re-emerging bacterial pathogen in freshwater and marine aquaculture worldwide, and there are no commercial vaccines available in the U.S. Researchers at the University of California, Davis, Mississippi State University, and USDA, ARS, Warmwater Aquaculture Research Unit collaborated to produce a live attenuated vaccine for this pathogen. Candidate vaccines were tested in Nile tilapia cell culture and fish and were highly effective. Along with the creation of tilapia-specific vaccines, this research demonstrated a pathway for effective vaccine creation against S. iniae for other fish species.

Technical Abstract: Streptococcus iniae is a re-emerging bacterial pathogen in freshwater and marine aquaculture worldwide. There are no commercial vaccines available for S. iniae in the United States, and autogenous vaccines are restricted to inactivated whole-cell preparations with limited protection against heterogenous strains. Live-attenuated vaccines (LAV) represent an advantageous alternative to these bacterins, as they induce robust cellular and humoral immunity, and may provide longer lasting protection through less stressful routes of administration. We investigated whether accumulation of mutations in S. iniae by serial passage in the presence of rifampin can generate immunogenic LAV conferring protection against challenge with heterologous wild-type (WT) S. iniae strains in Nile tilapia (Oreochromis niloticus). Three lineages of rifampin-resistant S. iniae strains were generated from three genetically distinct parent strains (n = 9) by multiple passages in increments of Rifamycin SV sodium salt. Growth in liquid media, extent of capsulation, antimicrobial susceptibility, survival in Nile tilapia whole blood, and cytotoxicity in an O. mossambicus endothelial cell line were compared between the passaged and WT strains. Nile tilapia challenges were used to assess strain virulence, generation of anti-S. iniae IgM, and the protection conferred by LAV candidates against virulent S. iniae. Rifampin-resistant strains demonstrated changes in growth rate and cytotoxicity in endothelial cells, as well as significant reductions in whole blood survival (p < 0.05). Selected strains also showed attenuated virulence in the Nile tilapia challenge model, and anti-S. iniae IgM generated against these strains demonstrated cross-reactivity against heterologous bacteria. Immunization by intracoelomic injection induced protection against a virulent WT strain of S. iniae, with relative percent survival up to 95.05%.