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ORIGINAL RESEARCH article
Front. Microbiol.
Sec. Infectious Agents and Disease
Volume 16 - 2025 | doi: 10.3389/fmicb.2025.1550544
Immune protective Test and Whole Genome Sequencing Analysis of the Attenuated Strain S02 of Streptococcus iniae
Provisionally accepted
Dandan Yi 1 Aiying Lei 2 Yu Liu 1 Guixiang Tong 2 Ting Huang 2 Chenyu Quan 3
Ming Chen 2
Liping Li 2*- 1 Guangxi University, Nanning, Guangxi Zhuang Region, China
- 2 Guangxi Key Laboratory of Aquatic Genetic Breeding and Healthy Aquaculture, Guangxi Academy of Fishery Sciences, Nanning, China
- 3 Key Laboratory of Veterinary Biotechnology, Guangxi Veterinary Research Institute, Nanning, Guangxi Zhuang Region, China
Streptococcus iniae (S. iniae) is one of the most serious diseases threatening tilapia aquaculture, causing huge economic losses every year. Injectable attenuated vaccines are still the best choice for preventing tilapia streptococcal diseases. This study evaluated the safety, stability, immunogenicity, antibody production time and immune dose of the attenuated strain S02 of S. iniae, and comprehensively analyzed the possible mechanisms of its attenuated virulence by the whole genome level. After detoxification, the S02 completely loses its pathogenicity to tilapia and has good immunogenicity. The results of the backpropagation safety test showed that S02 did not cause tilapia disease or death after continuous passage for 50 generations. After injected S02, the IgM level in the serum was significantly higher than that in the GX005 infection group within 28 d, and reached its peak at 14 d. Intraperitoneal injection of S02 with 10 9 CFUs/mL concentration of 0.2 mL had the best relative protection rate, which was 92.58%. The whole genome sequencing results showed that S02 had two 0.2 Mbp large segments of inversion compared to its parent virulence strain GX005, encoding 372 genes, including the virulence genes of the GNAT family N-acetyltransferase and the hyaluronic acid lyase genes of the hysA, hylA, and hylB, which are related to virulence factors. This study provides theoretical data support for the prevention and control the infection of S. iniae in tilapia. The abnormal expression of important virulence genes GNAT family N-acetyltransferase and hyaluronic acid lyase genes hysA, hylA, and hylB caused by the inversion and translocation of large fragments may be the main mechanism for their attenuated virulence. This study provided theoretical support for the prevention and treatment of Streptococcus iniae infection in tilapia and the application of S02 attenuated vaccine.
Keywords: Streptococcus iniae, Tilapia, Attenuated vaccine, immune protection, whole genome sequencing
Received: 23 Dec 2024; Accepted: 24 Mar 2025.
Copyright: © 2025 Yi, Lei, Liu, Tong, Huang, Quan, Chen and Li. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence:
Liping Li, Guangxi Key Laboratory of Aquatic Genetic Breeding and Healthy Aquaculture, Guangxi Academy of Fishery Sciences, Nanning, China
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