Genomic comparison of virulent and non-virulent serotype V ST1 Streptococcus agalactiae in fish

Rui Wang; Li-Ping Li; Ting Huang; Ai-Ying Lei; Yan Huang; Fu-Guang Luo; Dong-Ying Wang; Wei-Yi Huang; Ming Chen; Jun Huang

doi:10.1016/j.vetmic.2017.06.007

Genomic comparison of virulent and non-virulent serotype V ST1 Streptococcus agalactiae in fish

Vet Microbiol. 2017 Aug:207:164-169. doi: 10.1016/j.vetmic.2017.06.007. Epub 2017 Jun 13.

Authors

Rui Wang¹, Li-Ping Li², Ting Huang², Ai-Ying Lei², Yan Huang³, Fu-Guang Luo⁴, Dong-Ying Wang⁵, Wei-Yi Huang⁶, Ming Chen⁷, Jun Huang⁸

Affiliations

¹ Institute of Animal Science and Technology, Guangxi University, Nanning 530005, China; Guangxi Key Laboratory for Aquatic Genetic Breeding and Healthy Aquaculture, Guangxi Institute of Fisheries, Nanning 530021, China.
² Guangxi Key Laboratory for Aquatic Genetic Breeding and Healthy Aquaculture, Guangxi Institute of Fisheries, Nanning 530021, China.
³ Guangxi Center for Disease Control and Prevention, Nanning 530021, China.
⁴ Liuzhou's Aquaculture Technology Extending Station, Liuzhou 545006, China.
⁵ Institute of Animal Science and Technology, Guangxi University, Nanning 530005, China.
⁶ Institute of Animal Science and Technology, Guangxi University, Nanning 530005, China. Electronic address: wyhuang@gxu.edu.cn.
⁷ Guangxi Key Laboratory for Aquatic Genetic Breeding and Healthy Aquaculture, Guangxi Institute of Fisheries, Nanning 530021, China. Electronic address: cm990919@163.com.
⁸ Institute of Animal Science and Technology, Guangxi University, Nanning 530005, China. Electronic address: hj1351@163.com.

PMID: 28757019
DOI: 10.1016/j.vetmic.2017.06.007

Abstract

Streptococcus agalactiae or Group B Streptococcus (GBS) is the major pathogen causing pneumonia and meningitis in human, mastitis in dairy cows, and streptococcal disease in tilapia. Previous studies have shown that fish GBS strains are correlated with human GBS strains in evolution and might have cross-host infection ability. Although the invasive disease caused by ST1 GBS in non-pregnant adults and cows is increasing worldwide, infection of fish by ST1 GBS has not been reported. The aim of this study was to determine whether ST1 GBS was virulent in fish and to investigate the genomic characteristics of ST1 GBS strains with different pathogenicity in tilapia. The human-derived serotype V ST1 GBS strains NNA048 and NNA038 were used to intraperitoneally challenge Nile tilapia (Oreochromis niloticus) with doses of 1.0×10⁹CFU/fish, 1.0×10⁷CFU/fish, and 1.0×10⁵CFU/fish, respectively. The cumulative mortality rates of NNA048 infection at three different doses were 100.00%, 83.33%, and 40.00%. In contrast, there were no any sick or dead fish in NNA038 infection group. Histopathological results indicated that challenge of tilapia with NNA048 caused different degree of degeneration and necrosis in brain, liver, spleen, head kidney, and gut, and a large number of blue-stained Streptococcus granules were observed in the tissues. In contrast, there were no any lesions in the tissues of tilapia that were challenged with NNA038. Genome comparison showed that the major genome differences between NNA048 and NNA038 were attributed to the different phage sequences, and there was a 49.8kb length, intact phage sequence encoding 68 proteins in NNA048 genome. SNV and Indels analysis between NNA038 and NNA048 genomes indicated that there were a total of 96 SNVs, 5 deletions and 1 insert. Taken together, serotype V ST1 GBS was comprised of virulent and nonvirulent strains to tilapia, and gene rearrangement might be the main reason of causing different levels of virulence between strains.

Keywords: CC1; Gene rearrangement; Group B Streptococcus; Virulent.

MeSH terms

Animals
Cichlids*
Gene Expression Regulation, Bacterial
Genome, Bacterial
Genomics*
Phylogeny
Sequence Alignment
Serogroup
Streptococcal Infections / microbiology
Streptococcal Infections / veterinary*
Streptococcus agalactiae / genetics*
Streptococcus agalactiae / pathogenicity*
Virulence