Science Buddies: "Ask an Expert"

Hello! My 5th grader is doing the 'How Well Do Disinfectants Work?" experiment and we labeled the top of the dish and stored them that way (agar side down). 24 hrs later there is a lot of condensation on the top/non-agar side. After some googling we see that dishes should be stored agar side up so that condensation doesn't drip onto the agar and damage or slow colonial growth. We flipped them over but did we ruin the experiment? We have a very limited window to re-run the experiment if we did hence asking about it 1 day in. Thank you.

Hello! It's possible that the condensation did ruin parts of the results, or all of it. Some of the colonies may have been unaffected, but it is hard to know. After 24 hours, there should be some growth, especially on the control. I will ask someone who is very experienced growing bacteria on Petri dishes, and let you know what she says tomorrow, just to be extra sure.

That is very much appreciated, thank you!