Science Buddies: "Ask an Expert"

Hi, I did my science fair experiment on bacteria and which mouthwash works best. I did three trials for everything. I started with growing the bacteria for before each mouthwash and then did after a cinnamon and a peppermint. I counted the bacteria without researching it, so I just have a number of colonies. I recorded it day 1 and 2. I was wondering if there was a certain way I should record all of my data. Is there a way I could find a percent of the bacteria that was removed from the mouth? Or should I just make a data table and put the number of colonies I counted? Also, when I counted the number of colonies on day 2 were less than the number of colonies on day 1. Is that not accurate?

-Thanks,
Sarah

Hey Sarah,

Based on what you're telling me now, I think that just a number of colonies should be fine for comparison between the types of mouthwash so long as you repeated the same protocol to obtain those colonies each time. For example, if you used the same mouth and used mouthwash type 1 before breakfast one day, then try mouthwash type 2 before breakfast on another day (not right after type 1 since then the order of the treatments would matter). Or something to that effect.

Could you explain in more detail the exact protocol for what you did to obtain colonies, using the mouthwash? That would help a lot.

Hope this helps!
Aaron Lin

I did exactly that. On one day i swabbed the mouth before the mouthwash and then after the mouthwash. The next day, I swabbed before and after the second mouth wash. After I swabbed everything I put it into nutrient agar petri dishes and kept them in an incubator to grow them.

Hi!
Sounds like you're right on track! If you're looking to express your results in terms of a percentage, you could count the number of colonies before and after you applied the mouthwash and then divide the number of colonies after by the number of colonies before. Making a data table of this would be sufficient as well. Good luck!