Complex Population Structure and Virulence Differences among Serotype 2 Streptococcus suis Strains Belonging to
Taryn B T Athey1, Jean-Philippe Auger2, Sarah Teatero1
1Public Health Ontario, Toronto, Ontario, Canada.
Plos One
|September 17, 2015
Summary
The Streptococcus suis ST28 lineage shows surprising genetic diversity and varying virulence. Some strains, particularly those from the US, Thailand, and Japan, are more virulent and pose a greater risk for swine and human infections.
Area of Science:
- Veterinary Microbiology
- Genomics
- Zoonotic Diseases
Background:
- Streptococcus suis serotype 2 is a significant swine pathogen and zoonotic agent.
- Sequence type (ST) 28 of S. suis serotype 2 was previously considered a low-virulence, homogeneous group.
- However, ST28 strains are increasingly isolated from diseased swine and humans, suggesting potential virulence variations.
Purpose of the Study:
- To investigate the genetic diversity and virulence of Streptococcus suis ST28 strains.
- To determine if the ST28 lineage comprises strains with different genetic backgrounds and virulence levels.
- To assess the phylogenetic structure and geographic distribution of ST28 strains.
Main Methods:
- Whole-genome sequencing of 51 S. suis ST28 strains from Canada, the US, Japan, and Thailand.
- Phylogenetic analysis using core genome single-nucleotide polymorphisms (SNPs).
- Virulence testing in experimental animal infection models.
Main Results:
- Complex population structure identified within the ST28 lineage, driven by variable gene content, recombination, and polymorphisms.
- Phylogenetic analysis revealed four distinct clades with geographic structure and a fifth clade containing US, Thai, and Japanese strains.
- Strains from the fifth clade demonstrated significantly higher virulence in animal models compared to reference strains.
Conclusions:
- The S. suis ST28 lineage is genetically diverse and contains strains with varying virulence.
- Multilocus sequence typing (MLST) has limitations for accurate phylogenetic analysis and virulence prediction of S. suis.
- Emergence of virulent ST28 strains warrants concern for increased human clinical cases and swine disease.
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