Lecture Notes: Bacterial Structures and Their Functions

Cell Walls and Glycocalyx

• Cell Walls: Most bacteria have them.
• Glycocalyx: Additional structure outside the cell wall, known as a sugar coat.
  • Forms:
    • Capsule: Rigid, well-defined structure.
    • Slime Layer: Looser, less ordered structure.
  • Functions:
    • Contributes to virulence by evading phagocytosis.
    • Assists in attachment to surfaces.
    • Prevents drying out.
  • Biofilms: Formed by slime layers, associated with increased virulence and reduced sensitivity to antibiotics.

Capsules and Slime Layers

• Capsules can prevent India ink staining (negative staining).
• Biofilms result from the aggregation of slime layers.
• Mnemonic for remembering pathogens with capsules: "Even Some Super Killers Have Pretty Nice Big Capsules."

Flagella

• Structure: Filamentous protein enabling bacterial movement.
• Types:
  • Monotrichous: Single flagellum at one end.
  • Amphitrichous: Flagella at both ends.
  • Lopotrichous: Multiple flagella at one end.
  • Peritrichous: Flagella all over the surface.
• Movement: Driven by the rotation of flagella.
  • Chemotaxis: Movement towards/away from chemicals.
  • Phototaxis: Movement in response to light.
  • Mechanism: Rotate to run and tumble.
• Swarming Bacteria: Like Proteus mirabilis, exhibit swarming on agar plates and have a distinct smell.

Axial Filaments

• Found inside certain bacteria, such as those causing Lyme disease and syphilis.
• Examples:
  • Borrelia burgdorferi (Lyme disease)
  • Treponema pallidum (Syphilis)

Fimbriae and Pili

• Fimbriae:
  • Aid in surface adhesion.
  • Significant in biofilm formation and virulence (e.g., Neisseria gonorrhoeae in gonorrhea).
• Pili:
  • Facilitate lateral gene transfer.
  • Critical in sharing traits like antibiotic resistance through plasmid exchange.

Next Topic

• Discussion on eukaryotic cells and their primary substructures in the next lecture.