Micro-organisms (L2)

• Impact of Micro-organisms


  • Causes disease
  • Uses in agriculture
  • Impact on the food industry
  • Can affect the environment
  • Uses in pharmaceutical industry
• Koch's postulates


  A set of principles used to establish a causal relationship between a microorganism and a disease
• Eubacter

  • Human pathogens
  • Clinical or environmental
  • One kingdom
• Prokaryotes


  • Not compartmentalized
  • Cell membranes lack sterols (e.g. cholesterol)
  • Single circular chromosome
  • Ribosomal are 70S - subunits 30S (16S rRNA) and 50S (5S & 23S rRNA)
• Bacterial cell structure: plasmids, cell envelope, flagella, pili (fimbriae), wall-less forms of bacteria, capsules and slime layers, endospores
• Gram stain: Gram negative or gram positive
• Flagella


  • Some bacteria are motile
  • Locomotory organelles
  • Taste environment
  • Respond to food/poison
  • Move propeller-like action
• Pili (fimbriae)


  • Hair-like projections of the cell
  • Sexual conjugation
  • Adhesion to host epithelium
• Wall-less forms of bacteria

  • Result from action of enzymes lytic for cell wall or antibiotics inhibiting peptidoglycan biosynthesis
  • Usually non-viable
• Capsules and slime layers

  • Outside cell envelope
  • Usually polysaccharide
  • Often lost during in vitro culture
  • Protective in vivo
• Endospores


  • Dormant cell
  • Produced when starved
  • Resistant to adverse conditions
• Archaea

  • Environmental organisms
  • Second kingdom
• Gram negative:

  • major permeability barrier
  • periplasmic space (where degenerative enzymes are stored)
  • Braun lipoprotein attaches peptidoglycan layer to the outer membrane
  • contains endotoxins (lipopolysaccharides that make up the outer part of the outer membrane)
  • more resistant to penecillin
• Gram positive

  • no periplasmic space (degenerative enzymes are released externally)
  • lipoteichoic acid anchored the thick peptidoglycan cell wall to the membrane)
  • more susceptible to antibiotics and lysozyme than gram negative
• What is peotidoglycan made out of?

  N-acetylglucosamine and N-acetylmuramic acid
• Wall-less bacteria that don't replicate

  • Spheroplasts (with outer membrane)
  • Protoplasts (no outer membrane)
• Wall-less bacteria that replicate

  • L forms