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Name: Roy E.
Status: Other
Age: 30s
Location: N/A
Country: N/A
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. Good luck.


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