Science Buddies: "Ask an Expert"

My daughter and I are on the second time of trying this experiment. She is testing which gum is better for your teeth, mint, cinnamon, or fruit flavored. We had 9 volunteers and after chewing the gum for 5 minutes, swabbed their mouths and swiped on prepared petri dishes. We prepared the agar as directed and after 4 days there was no growth. I then ordered more agar to try again, we were precise with the swabbing and putting onto the agar. We did this last night and this morning there is still nothing growing. I have stored the petri dishes in a dark place and the temperature is about 68 degrees. Her results and data were due today, however her teacher has allowed her until Monday since the first time nothing happened. I am very nervous that nothing will happen again, as the project instructions stated there would be growth overnight. We do not have time to try again.....hopefully someone has some suggestions. Thank you!!

Hi Stephanie,

It sounds to me like your temperature might be a little too low. Think about the environment the bacteria normally live in (the mouth). You might need to try storing the plates somewhere a little closer to body temperature. Normal human bacteria need warm moist environments, and they thrive right around 35 to 37 C (98.6 F). What you really need is an incubator. And you can actually rig one up right at home pretty easily.

Here's just one example, but you should be able to find several more with a quick google search.
http://www.ehow.com/how_7908191_make-in ... teria.html

Hope that helps!

Thank you very much, I will give that a try!!
Stephanie