Strengthening of enterococcal biofilms by Esp

Area of Science:

• Microbiology
• Structural Biology
• Infectious Diseases

Background:

• Multidrug-resistant Enterococcus faecalis causes hospital-acquired infections.
• The enterococcal surface protein (Esp) is encoded by a pathogenicity island and its role in virulence and biofilm production is debated.

Purpose of the Study:

• To characterize the N-terminal region of Esp and its role in biofilm production and virulence.
• To investigate the structural and functional properties of Esp under varying pH conditions.

Main Methods:

• Small angle X-ray scattering and X-ray crystallography were used to determine the structure of the Esp N-terminal region.
• Biofilm strengthening assays were performed under different pH conditions.
• Protein stability assays were conducted on Esp fragments.

Main Results:

• The Esp N-terminal region has a globular head with two DEv-Ig domains and an extended tail.
• Esp strengthens existing biofilms against mechanical and degradative forces, enhancing bacterial retention.
• Biofilm strengthening is pH-dependent, with low pH inducing Esp unfolding, aggregation, and amyloid-like structure formation.
• A truncated Esp fragment demonstrated biofilm strengthening at pH ≤ 5.0, while intact Esp required pH ≤ 4.3.

Conclusions:

• Esp is not essential for initial biofilm formation but significantly enhances biofilm stability and bacterial retention.
• Esp's ability to strengthen biofilms is mediated by pH-induced structural changes, suggesting a virulence role in acidic environments.
• The stability of Esp and its fragments influences the pH threshold for biofilm strengthening.