Auto-aggregation in Streptococcus intermedius is driven by the Pel polysaccharide.

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• The Streptococcus milleri group (SMG) comprises opportunistic pathogens causing diverse infections.
• Pathogenic mechanisms in SMG, particularly auto-aggregation and biofilm formation, are poorly understood.
• Auto-aggregation is crucial for biofilm adhesion and cohesion in many bacterial species.

Purpose of the Study:

• To investigate the role of Pel exopolysaccharide production in Streptococcus intermedius biofilm formation and pathogenicity.
• To identify and characterize genes involved in Pel biosynthesis in S. intermedius.
• To understand how Pel production influences bacterial persistence and host immune interactions.

Main Methods:

• Identification of a S. intermedius gene cluster homologous to Bacillus cereus and Pseudomonas aeruginosa pel operons.
• Characterization of clinical S. intermedius isolates for aggregation and biofilm phenotypes.
• Genetic manipulation (gene deletion) to assess the function of identified genes in aggregation and Pel production.
• Biochemical analysis to identify the composition of the aggregated polymer.
• In vivo assessment using a mouse abscess model to evaluate the impact of Pel production on infection clearance.

Main Results:

• A S. intermedius gene cluster containing five canonical pel genes (pelDEA_DAFG) and four additional genes was identified.
• Aggregation phenotype in S. intermedius strain C1365 was dependent on the pelDEA_DAFG genes.
• Deletion of two additional genes (SIR_1592 and SIR_1594) partially reduced aggregation.
• SIR_1591 was identified as a glycoside hydrolase, and C1365 produces a GalNAc-rich polymer.
• Loss of Pel production in a ΔpelF mutant resulted in more effective bacterial clearance in a mouse abscess model.
• Pel production modulates S. intermedius interaction with the host immune system.

Conclusions:

• Pel exopolysaccharide biosynthesis is a significant contributor to S. intermedius pathogenicity.
• Pel production enhances bacterial persistence during infection and influences host immune responses.
• The identified pel gene cluster, including canonical and additional genes, plays a critical role in S. intermedius aggregation and biofilm formation.