Science Buddies: "Ask an Expert"

I doing an experiment testing which eczema cream retains the moisture. I have used gelatin as the skin. Everything is going well and I am upto day 3 testing. However this morning when weighing the petri dishes I found mound growing on all three control dishes. I have not covered the dishes because my thought was that humans do not cover their skin. I don't know what to. Any suggestions would be appreciated. Thank you

Hi Hasson,

Welcome to science buddies!

I think you are doing this excellent project.

https://www.sciencebuddies.org/science- ... #procedure

The project guide suggests putting the Jell-O plates in the refrigerator to solidify the gelatin, but then suggests leaving it out at ambient temperature for the remainder of the experiment. There is no special precaution about covering the plates or using sterile technique, so apparently there was no problem with mold contamination when the project idea was tested.

However, mold spores are ubiquitous (they are everywhere) and they will float down out of the air and start growing in any suitable medium. Jell-O contains water, protein, a slightly acidic pH, sugar and a solid surface, so is actually ideal for mold growth.

Unfortunately, molds can be toxic, especially after they form spores, so you should discard the moldy plates as quickly as possible. You can put them in a container, add 5% bleach and soak for an hour before discarding the plates in the trash, Be very careful and avoid breathing the air around your plates if the dark-colored spores have formed.

If you have time, you can set up your experiment again; I recommend using plain gelatin or sugar-free Jell-O to prevent mold growth. You should be able to use about 10% of the volume as isopropanol (rubbing alcohol) without affecting the solidification of the gelatin. After you make the gelatin plates, let them dry out so there's no visible moisture before you add the lotions. Do not let anyone eat the Jell-O if you add the isopropanol and do not use the isopropanol if there is any chance that someone might try to eat the Jell-O.

If you don't have time to repeat your experiment, don't worry. You did your experiment and obtained results for the first few days, but you had to discard the plates because of the mold contamination. It's unfortunate that your controls were affected by the mold. Your discussion section should contain information about why the mold grew in your plates, and how you would avoid the problem in the future. You can continue measuring results on any plates that do not contain mold, but discard the plates if more mold appears.

I will report the problem to Science Buddies for review. We may want to modify the procedure for the future to avoid the possibility of mold contamination.

Please let me know if you have any questions.



Donna

Hi Donna,
Thank you so much for your advice. I do have enough time to redo the experiment. Thanks for the tips. I will redo the gelatin adding the isopropanol. I will post up my new results and hopefully that will help others too.
Thanks,
Hassan

Hi Hassan,
Thanks for your reply. Don't worry if you don't have time to set up the experiment again. You did the experiment and obtained unexpected results. This is perfectly acceptable in science fair projects. Since your controls molded, your results will be inconclusive, but you will have a great discussion and conclusion.

I thought of a better way to inhibit mold growth. Just add a teaspoon of baking soda to the Jell-O; this will inhibit mold growth with a high pH. Using isopropanol would work also, but probably not a good idea if there are any small children or dogs around that might mistake the experiment for food.

Good luck!

Donna