Extracellular matrix formation enhances the ability of Streptococcus pneumoniae to cause invasive disease

Area of Science:

• Microbiology
• Pathogenesis
• Bacterial biofilms

Background:

• Pneumococci predominantly form sessile biofilms during infection, differing from their planktonic state.
• The role of these biofilms in pneumococcal pathogenesis remains largely unexplored.

Purpose of the Study:

• To investigate the contribution of pneumococcal biofilm variants to pathogenesis.
• To identify genetic factors involved in biofilm formation and disease progression.

Main Methods:

• Biofilm assays were performed on opaque and transparent variants of Streptococcus pneumoniae strain WCH159.
• Scanning electron microscopy (SEM) was used to visualize biofilm structure.
• Murine models were used to assess bacterial translocation.
• In vitro adherence assays were conducted using A549 cells.
• Microarray analysis identified differentially expressed genes.

Main Results:

• Opaque variants formed an extracellular matrix, unlike transparent variants.
• Opaque biofilm bacteria demonstrated enhanced translocation from nasopharynx to lungs and brain in mice.
• Opaque bacteria exhibited significantly higher in vitro adherence to A549 cells.
• Differential gene expression was observed in the lic operon and ciaRH two-component system.
• Mutants lacking functional lic operon or ciaRH failed to form extracellular matrix, showed impaired translocation, and poor adherence.

Conclusions:

• The opaque phenotype is essential for extracellular matrix production in pneumococcal biofilms.
• The lic operon and ciaRH are critical for extracellular matrix formation.
• Extracellular matrix production by biofilms significantly contributes to pneumococcal adherence, translocation, and invasive disease potential.