The sbp3 gene of Streptococcus suis plays an important role in biofilm formation, adhesion, invasion, and cytotoxicity in the human intestinal epithelial cell line

  • Microb Pathog. 2026 Jul:216:108496. doi: 10.1016/j.micpath.2026.108496.
Siriwan Sunontarat  1 ,  Thotsaporn Bunthiang  1 ,  Nattamol Phetburom  1 ,  Peechanika Chopjitt  1 ,  Bhanubong Saiboonjan  2 ,  Patcharaporn Tippayawat  2 ,  Surachat Buddhisa  3 ,  Rujirat Hatrongjit  4 ,  Suphachai Nuanualsuwan  5 ,  Anusak Kerdsin  1 ,  Parichart Boueroy  6
Affiliations
  • 1. Faculty of Public Health, Kasetsart University Chalermphrakiat Sakon Nakhon Province Campus, Sakon Nakhon, Thailand.
  • 2. Division of Clinical Microbiology, Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand; The Center for Research & Development of Medical Diagnostic Laboratories, Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand.
  • 3. Department of Medical Technology, Faculty of Allied Health Sciences, Burapha University, Chonburi, Thailand.
  • 4. Department of General Sciences, Faculty of Science and Engineering, Kasetsart University Chalermphrakiat Sakon Nakhon Province Campus, Sakon Nakhon, Thailand.
  • 5. Department of Veterinary Public Health, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand; Center of Excellence for Food and Water Risk Analysis (FAWRA), Department of Veterinary Public Health, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand.
  • 6. Faculty of Public Health, Kasetsart University Chalermphrakiat Sakon Nakhon Province Campus, Sakon Nakhon, Thailand; Department of Veterinary Public Health, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand; Center of Excellence for Food and Water Risk Analysis (FAWRA), Department of Veterinary Public Health, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand. Electronic address: [email protected].
PMID: 42000057 DOI: 10.1016/j.micpath.2026.108496
Abstract

Streptococcus suis is a zoonotic pathogen that causes severe infections in pigs and humans. Pilus are critically involved in Bacterial adhesion, invasion, and biofilm formation, but the role of the pilin protein SBP3 in the srtBCD cluster remains unclear. This study characterized the role of the sbp3 mutant on human intestinal epithelial Caco-2 cells, compared to the wild-type (WT) strain. Knockout of sbp3 (Δsbp3) did not markedly affect overall Bacterial growth. Biofilm formation by the Δsbp3 mutant was significantly impaired, with reduced biofilm observed at 2-72 h (p < 0.01). In addition, the Δsbp3 mutant significantly decreased Bacterial adhesion to Caco-2 cells at MOI 1 (p < 0.001) and MOI 10 (p < 0.01). Furthermore, the SEM analysis demonstrated the role of sbp3 in Bacterial adhesion to epithelial cells as it was associated with fewer membrane protrusions. The invasion capacity of the Δsbp3 mutant was significantly reduced at MOI 1 (p < 0.05), whereas no significant difference was observed at MOI 10. Furthermore, the Δsbp3 mutant resulted in lower cytotoxicity in Caco-2 cells than WT after Infection at 2, 4, and 18 h. In addition, the Δsbp3 mutant exhibited significantly reduced hemolytic activity (p < 0.001), which was consistent with the mRNA levels of sly. These findings indicated that sbp3 plays a key role in promoting epithelial attachment and host cell damage, supporting its broader contribution to multiple virulence-associated traits. This highlights sbp3 as a potential target for strategies aimed at preventing or controlling infections in both pigs and humans.

Keywords
Adhesion; Biofilm; Cytotoxicity; Pilus; Streptococcus suis; sbp3.
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