Lecture Notes: Bacterial Pathogenesis - Attachment and Invasion

Introduction

• Bacterial Pathogenesis: Study of how bacteria cause disease.
• Focus: Attachment (Adherence) and Invasion.

Attachment (Adherence)

• Definition: Ability of bacteria to stick to body cells.
• Key Structures:
  • Adhesins: Molecules that help in attachment.
  • Pili/Fimbriae: Hair-like projections aiding in attachment.
• Functions:
  • Pili also function as sex pili for conjugation.

Invasion

• Types:
  • Passive Invasion: Bacteria enter through wounds/cuts without active involvement.
  • Active Invasion: Bacteria actively penetrate cells using invasins.

Example 1: EPEC (Enteropathogenic E. coli)

• Relevance: Some E. coli strains cause foodborne illnesses.
• Attachment Process:
  1. Initial Engagement: Using Bundle Forming Pili (BFP) to interact with gut epithelial cells.
  2. Generalized Attachment: Ensures bacteria remain attached despite gut movements.
  3. Intimate Attachment:
     • Uses Type 3 Secretion System (TTSS), a syringe-like mechanism.
     • Injects proteins into host epithelial cells.
     • Protein TIR is introduced as a receptor in host cells, binds with bacterial Intimin.
     • Results in pedestal formation, a strong binding mechanism.

Example 2: Salmonella

• Objective: Invade host cells and spread systemically.
• Invasion Process:
  1. Interaction with Gut Epithelial Cells: Initial engagement using invasins.
  2. Usage of Type 3 Secretion System:
     • Injects proteins affecting actin cytoskeleton.
     • Causes membrane ruffling, leading to engulfment of bacteria by epithelial cells.
  3. Outcome: Bacteria are inside host cells, enabling further spread.

Conclusion

• Both EPEC and Salmonella utilize specific mechanisms for attachment or invasion, using structures like pili and sophisticated secretion systems.
• Understanding these processes is crucial for studying bacterial pathogenesis.
• Visual Aids: Animations available for better understanding of these mechanisms.