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Why doesnt sugar rot?

  1. Aug 28, 2007 #1
    So what does it take for bacteria to find something tasty?
     
  2. jcsd
  3. Aug 28, 2007 #2

    jim mcnamara

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    rot is usually a fungal thing.

    The reason dry sugar doesn't decay is because it has so little water no organism can grow on it.

    Syrups will show a fungal mat on the exposed surface after a while. But, again, water limits most organisms from growing on syrup due to extreme ex-osmotic (water movement out of the cells) pressures. Fungi don't seem to mind this as much as do other microbes.

    If you want activity: make about a 20% sugar solution, let it sit exposed for a few days.
     
  4. Aug 28, 2007 #3

    mgb_phys

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    Bacteria find sugar very tasty, you grow them on Agar - a type of sugar.
    As Jim said, the problem is that sugar absorbs water very strongly. If a bacteria lands on sugar this effect is so strong that the water from inside the bacteria is pulled out into the sugar and the bacteria die.
     
  5. Aug 28, 2007 #4

    jim mcnamara

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    Agar is a sulfated polymer of galactose. It is essentially devoid of free simple sugars. Microbes are usually grown on a medium that has bacteria-style nutrition mixed into an agar solution. Agar solutions are liquid above ~45C and don't mind being autoclaved. Which is why agar is used.

    Agar acts as a support medium, like a gelatin.
     
  6. Aug 28, 2007 #5

    mgb_phys

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    Thanks - I was just trying to simplify the 'osmotic pressure' explanation.
     
  7. Aug 28, 2007 #6

    DaveC426913

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    More simply, sugar, like salt, is a dessicant.
     
  8. Sep 4, 2007 #7
    Pardon me for jumping in but there's something I've been wondering about. What if a microbial pathogen were engineered to mimic the properties of the standard growing medium. Would it be able to hide in plain sight, so to speak?
     
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