Why Doesn't Sugar Rot? Bacteria & Tasty Treats

[pikapika!]

So what does it take for bacteria to find something tasty?

 

[jim mcnamara]

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.

 

[mgb_phys]

So what does it take for bacteria to find something tasty?

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.

 

[jim mcnamara]

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.

 

[mgb_phys]

Thanks - I was just trying to simplify the 'osmotic pressure' explanation.

 

[DaveC426913]

More simply, sugar, like salt, is a dessicant.

 

[Far Star]

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?