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Bacterial Structures

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Topic updated on 07/12/17 6:20pm

Structures contributing to virulence
  •  Flagella
    • protein filament "tails" that allow movement and chemotaxis
      • Vibrio cholera - 1 flagella
      • E. coli - many flagella
      • Shigella - no flagella
  • Pili (fimbria)
    • shorter than flagella and immobile
    • allows some bacteria to adhere to their host
      • Neisseria
      • E. coli
    • sex pili are special types of pili used for conjugation rather than virulence
    • made of glycoproteins
  • Capsules
    • prevent phagocytosis
    • made of polysaccharide
      • except Bacillus anthracis, which contains D-glutamate
  • Endospores
    • only Bacillus and Clostridium
    • dormant form
      • no metabolic activity
    • confers resistance to hot/cold, wet/dry, and host chemical defenses
      • must autoclave to kill
    • formed at the end of stationary phase
      • when nutrients are in short supply
    • dipicolinic acid may confer heat resistance 
Other structures
  • Cell wall (Gram-positive) This illustration highlights the basic bacterial structures in gram positive and gram negative bacteria. LPS = Lipopolysaccharides; PBP = Penicillin-binding proteins.
    • contains the major surface antigens of Gram-positive bacteria
      • e.g. teichoic acid → activates TNF and IL-1
    • Mycoplasma has no cell wall
    • Mycobacteria has unusual cell wall
  • Outer membrane (Gram-negative)
    • source of endotoxin in Gram-negative bacteria
  • Peptidoglycan
    • structural support
    • polymer of sugars and amino acids
  • Plasma membrane
    • composed of a lipoprotein bilayer
  • Ribosome
    • 50S and 30S subunits
    • protein synthesis
  • Plasmid
    • DNA that is separate from and replicates independently of chromosomal DNA
    • can contain genes for antibiotic resistance and toxins
  • Periplasm
    • in Gram-negative bacteria, the space between the outer membrane and the cytoplasmic membrane
    • contains β-lactamases or other hydrolytic enzymes
  • Glycocalyx
    • polysaccharide that helps bacteria adhere to host surfaces
      • e.g. catheter-associated infection


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