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Pathogenic characteristics of an unencapsulated Streptococcus suis serotype 31 strain isolated from a patient in

Parichart Boueroy1, Nattamol Phetburom2, Sorujsiri Chareonsudjai3,4

  • 1Faculty of Public Health, Kasetsart University Chalermphrakiat Sakon Nakhon Province Campus, Sakon Nakhon, Thailand. parichart.bou@ku.th.

Scientific Reports
|October 30, 2025
PubMed

Insights

This study shows that the unencapsulated Streptococcus suis serotype 31 strain 43640 invades epithelial cells and causes septicemia in mice. This emerging clone is potentially virulent, highlighting the need for further investigation into Streptococcus suis virulence mechanisms.

Area of Science:

  • Microbiology
  • Infectious Diseases
  • Pathogen Virulence

Background:

  • Streptococcus suis is a zoonotic pathogen causing invasive infections.
  • An unencapsulated S. suis serotype 31 strain (ST221) was isolated from a human in Thailand.
  • Limited data exists on serotype 31's host-cell interactions and virulence.

Purpose of the Study:

  • To determine the virulence of the human unencapsulated S. suis serotype 31 strain 43640.
  • To investigate its interaction with host cells in vitro and its pathogenicity in vivo.

Main Methods:

  • In vitro assays using A549 epithelial cells to assess adhesion, invasion, cytotoxicity, and apoptosis.
  • In vivo studies using a C57BL/6 mouse model to evaluate mortality and bacterial load in blood.

Main Results:

  • Strain 43640 showed lower adhesion but higher invasion rates compared to S. suis serotype 2.
  • S. suis serotype 31 induced significant cytotoxicity and caspase 9-dependent apoptosis in epithelial cells.
  • In mice, strain 43640 caused septicemia with 46.67% mortality at 48 hours and lower bacterial counts than the reference strain.

Conclusions:

  • The unencapsulated S. suis serotype 31 strain 43640 exhibits potentially virulent characteristics.
  • ST221 represents an emerging virulent S. suis clone in Thailand.
  • Further research is needed to elucidate serotype 31 virulence mechanisms.
Keywords:
Streptococcus suis serotype 31ApoptosisCytotoxicitySurvival rateVirulence

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