Investigation of genomic and pathogenicity characteristics of Streptococcus suis ST1 human strains from Guangxi Zhuang Autonomous Region (GX) between 2005 and 2020 in China

ABSTRACT

Streptococcus suis is a significant and emerging zoonotic pathogen. ST1 and ST7 strains are the primary agents responsible for S. suis human infections in China, including the Guangxi Zhuang Autonomous Region (GX). To enhance our understanding of S. suis ST1 population characteristics, we conducted an investigation into the phylogenetic structure, genomic features, and virulence levels of 73 S. suis ST1 human strains from GX between 2005 and 2020. The ST1 GX strains were categorized into three lineages in phylogenetic analysis. Sub-lineage 3-1a exhibited a closer phylogenetic relationship with the ST7 epidemic strain SC84. The strains from lineage 3 predominantly harboured 89K-like pathogenicity islands (PAIs) which were categorized into four clades based on sequence alignment. The acquirement of 89K-like PAIs increased the antibiotic resistance and pathogenicity of corresponding transconjugants. We observed significant diversity in virulence levels among the 37 representative ST1 GX strains, that were classified as follows: epidemic (E)/highly virulent (HV) (32.4%, 12/37), virulent plus (V+) (29.7%, 11/37), virulent (V) (18.9%, 7/37), and lowly virulent (LV) (18.9%, 7/37) strains based on survival curves and mortality rates at different time points in C57BL/6 mice following infection. The E/HV strains were characterized by the overproduction of tumour necrosis factor (TNF)-α in serum and promptly established infection at the early phase of infection. Our research offers novel insights into the population structure, evolution, genomic features, and pathogenicity of ST1 strains. Our data also indicates the importance of establishing a scheme for characterizing and subtyping the virulence levels of S. suis strains.

KEYWORDS:

• Streptococcus suis
• ST1
• 89K-lke PAIs
• virulence
• TNF-α

Acknowledgements

We are grateful to Jingdong Song (National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention) for the technical support of transmission electron microscopy. HZ and JX designed the project; HZ drafted the manuscript; MG and ZW reviewed the manuscript. WK, WM, XY, JW, XZ, ZW, and HS carried out the experiments and generated the data; WK, YW, ZW, and HZ analyzed the data. All authors have read and approved the final version of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the [National Natural Science Foundation of China] under Grant [Number 81572044]; [Priority Project on Infectious Disease Control and Prevention from the Ministry of Science and Technology of the People's Republic of China] under Grant [Number 2017ZX10303405-002]; [State Key Laboratory of Infectious Disease Prevention and Control] under Grant [Number 2022SKLID208].