Name: Roy E.
Date: March 2004
My son has a science fair project in which he is
comparing anti-bacterial cleaners. We have been unable to get the
bacteria to grow even in our control group. Our instructions were to
leave an egg at room temperature for a couple of hours to use as the
source of our bacteria. Then we used unflavored gelatin with a beef
bullion cube added to it as the food source for the bacteria. My question
is where could we get a rather harmless bacteria to use for this
experiment and will the gelatin beef bullion mixture work for the food
source to grow the bacteria in?
I found this recipe for homemade media online:
"Mix 1 boullion cube (I used beef, don't know if it makes a difference) in 100
ml water. Add 10 ml of this to 40 ml water. Add 2 pkg Knox gelatin and heat.
Pour into petri plates. A substitute for petri plates is those little glass
dishes you put under furniture casters.
This recipe produces an enriched gelatin material which various
microorganisms will grow on similarly to an enriched agar medium. The
problem with using gelatin as the base is that many microorganisms release
proteases which will digest the gelatin (it's protein-based), causing it to
liquify. Agar is preferentially used because it is a carbohydrate
derivative and thus unaffected by proteinases. It will retain its gelled
characteristic while gelatin turns to soup."
I would say that maybe by adding a little sugar you could increase your yield-all living things need a source of carbohydrate. Bacteria are everywhere! If your son just took a Q tip and swiped the countertop or the floor and rubbed it on a plate of your agar he should get lots of bacteria. He could even leave a plate open to the air overnight and then close it and bacteria and mold should grow. He could then transfer some that looked interesting to another plate.
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