Sept 29, 2008 notes

Factors the influence bacterial growth

• Osmotic Pressure
  • The pressure put on a cell because of the movement of water
  • Too little concentration of water sucks the water out of the bacterium, causing it to shrivel
  • Too much concentration of water flows into the the bacterium, causing it to explode
• Water Activity
  • How much available water in given environment
  • Examples
    • pure water = 1.0 water activity (w.a.)
    • human blood = .995 w.a.
    • honey= .90 w.a. - S. aureus and S. epidermiditis can grow here!!
  • Bacteria can't survive if environmental conditions are too different from that bacteria's ideal growth conditions
  • Halophiles:able to survive in very low water activity
    • this ability comes from raising the concentration of solute on inside of cell
  • "Salt in a Wound"
    • Sucks the water out of bacterial AND our cells, so it HURTS because its killing our cells, but preventing infections.