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Streptococcus suis Serotype 2 Biofilms Inhibit the Formation of Neutrophil Extracellular Traps
Fang Ma1, Li Yi2, Ningwei Yu1
1College of Veterinary Medicine, Nanjing Agricultural University Nanjing, China.
Abstract:
Invasive infections caused by Streptococcus suis serotype 2 (SS2) has emerged as a clinical problem in recent years. Neutrophil extracellular traps (NETs) are an important mechanism for the trapping and killing of pathogens that are resistant to phagocytosis. Biofilm formation can protect bacteria from being killed by phagocytes. Until now, there have only been a few studies that focused on the interactions between bacterial biofilms and NETs. SS2 in both a biofilm state and a planktonic cell state were incubated with phagocytes and NETs, and bacterial survival was assessed. DNase I and cytochalasin B were used to degrade NET DNA or suppress phagocytosis, respectively. Extracellular DNA was stained with impermeable fluorescent dye to quantify NET formation. Biofilm formation increased up to 6-fold in the presence of neutrophils, and biofilms were identified in murine tissue. Both planktonic and biofilm cells induced neutrophils chemotaxis to the infection site, with neutrophils increasing by 85.1 and 73.8%, respectively. The bacteria in biofilms were not phagocytized. The bactericidal efficacy of NETs on the biofilms and planktonic cells were equal; however, the biofilm extracellular matrix can inhibit NET release. Although biofilms inhibit NETs release, NETs appear to be an important mechanism to eliminate SS2 biofilms. This knowledge advances the understanding of biofilms and may aid in the development of treatments for persistent infections with a biofilm component.
Insights
Neutrophil extracellular traps (NETs) help clear Streptococcus suis serotype 2 (SS2) infections. While SS2 biofilms can hinder NET release, NETs remain crucial for eliminating these resilient bacterial communities.
Area of Science:
- Microbiology
- Immunology
- Infectious Diseases
Background:
- Invasive infections caused by Streptococcus suis serotype 2 (SS2) are a growing clinical concern.
- Neutrophil extracellular traps (NETs) are a key defense mechanism against phagocytosis-resistant pathogens.
- Bacterial biofilms protect microbes from host immune responses, but their interaction with NETs is underexplored.
Purpose of the Study:
- To investigate the interaction between Streptococcus suis serotype 2 (SS2) biofilms and neutrophil extracellular traps (NETs).
- To assess the impact of SS2 in both biofilm and planktonic states on neutrophil activity and bacterial survival.
- To determine the efficacy of NETs in combating SS2 biofilms.
Main Methods:
- Incubation of SS2 (biofilm and planktonic states) with phagocytes and NETs.
- Assessment of bacterial survival, neutrophil chemotaxis, and NET formation.
- Utilized DNase I to degrade NET DNA and cytochalasin B to inhibit phagocytosis.
- Quantified NET formation using impermeable fluorescent dye staining for extracellular DNA.
Main Results:
- Biofilm formation by SS2 increased up to 6-fold in the presence of neutrophils, with biofilms observed in murine tissue.
- Both planktonic and biofilm SS2 induced significant neutrophil chemotaxis.
- Bacteria within biofilms were protected from phagocytosis.
- NETs exhibited equal bactericidal efficacy against planktonic and biofilm SS2, but the biofilm matrix inhibited NET release.
- NETs were identified as crucial for eliminating SS2 biofilms despite matrix-induced inhibition.
Conclusions:
- Neutrophil extracellular traps (NETs) play a significant role in controlling Streptococcus suis serotype 2 (SS2) infections, including those involving biofilms.
- While SS2 biofilms can impede NET formation, NETs remain effective in eliminating these structures.
- Understanding the interplay between SS2 biofilms and NETs can inform strategies for treating persistent bacterial infections.
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