Lecture on Capsules and Biofilms

Introduction to Capsules

• Capsule Definition: A type of glycocalyx, which is a sticky sugar coat produced by microorganisms.
• Composition: Made up of gelatinous, sticky polymer substances that can include carbohydrates and proteins.
• Function: Coats microorganisms, providing a protective layer.
• Types:
  • Slime Layer: Loosely organized and unstructured.
  • Capsule: Neatly organized, important for virulence.

Relationship to Biofilms

• Capsules vs. Biofilms:
  • Capsules are akin to a biofilm for a single organism.
  • Biofilms are sticky substances that cover groups of organisms.
• Significance of Biofilms:
  • Responsible for around 70% of human infections according to the CDC.

Importance of Capsules

• Increases Virulence: Helps organisms evade phagocytosis.
  • Phagocytosis: Process by which immune cells like macrophages and neutrophils engulf and destroy bacteria.
• Examples of Capsule Impact:
  • Bacillus anthracis (Anthrax)
    • Pathogenic with capsule, non-pathogenic without.
  • Streptococcus pneumoniae
    • Frederick Griffith’s experiments showed it causes pneumonia with a capsule.
    • Responsible for diseases like pneumonia, sepsis, and meningitis, causing 1.4-1.5 million deaths annually.
  • Klebsiella pneumoniae
    • Pathogenic with capsule, non-pathogenic without.

Conclusion

• Virulence and Pathogenicity: Capsules make organisms more dangerous by helping them evade immune defenses.
• Capsules as Biofilms: Keep in mind the analogy of capsules being a biofilm for an individual organism, a topic to be explored further in future discussions.