Science Buddies: "Ask an Expert"

I am conducting the germ invasion experiment, with a few modifications. I will place 2 Petri dishes each in 3 public places. A public bathroom, a public kitchen, and a public workspace. On one of these Petri dishes will be the antiseptic Iodine Compound. The other Petri dish will be fully exposed with no lid, or antiseptic on it. I will test each location 3 times, determining the average.

My 3 questions are:
1) How do I apply Iodine Compound onto the petri dish?
2) How much Iodine Compound should I use for each petri dish?
3) How should I count the microbial growth?

Thank you, Emily M.

Hi Emily,

Sorry no one has answered your question. I will try.

I can't tell you how much iodine compound to use because that should be one of your independent variables. The problem I see will be getting an even film of the iodine compound on the surface of the agar. If the iodine solution is in a spray bottle then it will be easy to simply spray the surface of the agar. If it is just a liquid in a bottle it will be harder to get a uniform application on the agar surface.

If you can buy a small spray bottle you could use that for applying the iodine solution.

I would recommend testing two compounds--the iodine and one other spray, like Lysol. That way you will have two to compare and that makes the story more interesting. Iodine solutions like Betadine are usually applied to the skin while Lysol is sprayed on surfaces to disinfect them.

If you have more questions, let me know.

Sybee