Extracellular polymeric substances

EPS Composition - The Biofilm's Glue

• Major Components: A hydrated matrix (~97% water) primarily composed of:
  • Polysaccharides: The main structural scaffold. Key examples include Alginate (Pseudomonas aeruginosa), Cellulose (E. coli, Salmonella), and Glucans (Streptococcus mutans).
  • Proteins: Functional (e.g., enzymes like hydrolases, nucleases) and structural (e.g., amyloid fibers like curli, fimbriae).
  • eDNA (extracellular DNA): Released via cell lysis; critical for initial adhesion, structural stability, and horizontal gene transfer.
  • Lipids & Surfactants: Contribute to biofilm structure and facilitate motility.

⭐ Alginate, an exopolysaccharide from Pseudomonas aeruginosa in Cystic Fibrosis patients, is a key virulence factor that confers significant antibiotic resistance.

EPS Functions - Slime Shield Activated

• Structural Scaffold: Provides the 3D architecture for the biofilm community.
• Adhesion & Cohesion: Mediates initial attachment to surfaces (e.g., catheters, teeth) and cements bacteria together.
• Protective Barrier:
  • Shields from host immunity (phagocytes, antibodies, complement).
  • Limits penetration of antimicrobial agents, often ↑ MIC by 100-1000x.
  • Prevents desiccation by retaining water.
• Nutrient Reservoir: Sequesters ions and can be degraded for use as a carbon source during starvation.
• Genetic Exchange Hub: Creates a stable environment facilitating horizontal gene transfer.

⭐ High-Yield: The EPS matrix is a primary reason for the profound antibiotic resistance of biofilms. It acts as a diffusion barrier, slowing drug penetration and allowing bacteria time to activate stress responses.

📌 Mnemonic: "SHIELD"

• Structural support
• Hydration
• Immune evasion
• Environment for exchange
• Location (adhesion)
• Diet (nutrients)

matrix protecting bacteria from antibiotics and immune cells)

Clinical Relevance - Resistance & Virulence

• Antibiotic Resistance: Biofilms create a formidable barrier against antimicrobial agents.

  • Physical Barrier: The dense EPS matrix physically blocks or slows the diffusion of antibiotics.
  • Chemical Inactivation: Enzymes trapped within the EPS (e.g., β-lactamases) can degrade antibiotics like penicillin.
  • Altered Metabolism: Bacteria in deeper layers are often in a slow-growing or dormant state (persister cells), making them less susceptible to antibiotics that target active cell processes.

• Host Immune Evasion:

  • The EPS matrix shields bacteria from phagocytosis and antibodies.
  • Contributes to chronic infections by frustrating immune clearance (e.g., Pseudomonas aeruginosa in cystic fibrosis).

⭐ Biofilm-associated bacteria can be up to 1000-fold more resistant to antibiotics than their free-floating (planktonic) counterparts.

High‑Yield Points - ⚡ Biggest Takeaways

• The Extracellular Polymeric Substance (EPS) is the structural "slime" matrix of biofilms, providing protection and adhesion.
• It's a complex mixture of polysaccharides, proteins, lipids, and extracellular DNA (eDNA).
• EPS is critical for adhesion to surfaces, especially medical devices like catheters and implants.
• It acts as a physical barrier, shielding microbes from antibiotics and host immune responses.
• eDNA in the matrix facilitates horizontal gene transfer, promoting the spread of resistance.
• Directly contributes to the persistence and chronic nature of biofilm-associated infections.