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Updated: Apr 30 2022

Bacterial Structures

Images
https://upload.medbullets.com/topic/104001/images/cellwalls.jpg
https://upload.medbullets.com/topic/104001/images/virulence.jpg
https://upload.medbullets.com/topic/104001/images/bacterial structures.jpg
  • 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)
      • 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
      • disruption leads to osmotic lysis
    • 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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