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

Taylor I Heckman; Khalid Shahin; Eileen E Henderson; Matt J Griffin; Esteban Soto

doi:10.1016/j.fsi.2021.12.043

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

Fish Shellfish Immunol. 2022 Feb:121:152-162. doi: 10.1016/j.fsi.2021.12.043. Epub 2021 Dec 26.

Authors

Taylor I Heckman¹, Khalid Shahin², Eileen E Henderson³, Matt J Griffin⁴, Esteban Soto⁵

Affiliations

¹ Department of Medicine & Epidemiology, School of Veterinary Medicine, University of California, Davis, CA, 95616, USA.
² Department of Medicine & Epidemiology, School of Veterinary Medicine, University of California, Davis, CA, 95616, USA; Aquatic Animals Diseases Laboratory, Aquaculture Division, National Institute of Oceanography and Fisheries, P.O. Box 43511, Suez, Egypt.
³ California Animal Health and Food Safety Lab, School of Veterinary Medicine, University of California, Davis, CA, 92408, USA.
⁴ Department of Pathobiology and Population Medicine, College of Veterinary Medicine, Mississippi State University, Stoneville, MS, 39762, USA.
⁵ Department of Medicine & Epidemiology, School of Veterinary Medicine, University of California, Davis, CA, 95616, USA. Electronic address: sotomartinez@ucdavis.edu.

PMID: 34965443
DOI: 10.1016/j.fsi.2021.12.043

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%.

Keywords: Aquaculture; Streptococcosis; Streptococcus iniae; Tilapia; Vaccine.

MeSH terms

Animals
Bacterial Vaccines / immunology*
Cell Line
Cichlids* / immunology
Endothelial Cells / microbiology
Fish Diseases* / prevention & control
Immunoglobulin M
Rifampin
Streptococcal Infections* / prevention & control
Streptococcal Infections* / veterinary
Streptococcus iniae
Vaccines, Attenuated / immunology

Substances

Bacterial Vaccines
Immunoglobulin M
Vaccines, Attenuated
Rifampin