The 5 Second Rule and Bacteria Transfer

[SheylaM]

Hello, I am doing a science fair project about the 5 Second rule. I have conducted my experiment, but I'm a little insecure about my results. The bacteria grew in room temperature, I didn't see anything until day 6. I had to wait for the bacteria to grow for almost a week, I expected that to happen because of the temperature. I'm trying to figure out if bacteria does tranfer in less than 5 seconds, I'm using different types of floor and instead of food, cotton swabs just like my teacher told me. The 5 different types of floor were: marble floor, hardwood floor, ceramic floor, blacktop, and carpet floor. When I threw the q-tip on the blacktop for 2 seconds, I didn't expect any bacteria to grow because my hypothesis was that bacteria wouldn't transfer if the cotton swabs remained on the floor for less than 5 seconds, but I saw 8 bacterial colonies. My question are: Do my results look illogical? Any advice? How much bacterial colonies should I normally see? Is it normal for the agar to turn blue? Thank you!

[PharmaMan]

Hi Sheyla,

Your results don't seem illogical. It seems the results are confirming that very small amounts of bacteria can transfer to the cotton swab in a very short amount of time. I'm not sure how many colonies you should normally see, but I expect that you will likely see several separate colonies. Because the number of cells being transferred to the swab is likely very low, it will take a number of days for them to grow up to be visible. This is especially true since your experiments are done at room temperature.

How are you doing the experiment in terms of transferring the samples to the agar? I don't know what it means by the agar turning blue, but the agar should remain a consistent color. Are you using a special type of agar? Also, what time points are you using for your experiments?

-Pharma

[nguyenmccarty]

Hi Sheyla,

I agree with PharmaMan's points. I just want to point out one very important control (which you may already be doing!). You need to make sure that you have one sample where you didn't put the Q-tip on any type of floor at all: the Q-tips themselves almost certainly already have a (hopefully small) amount of bacteria on them, so you need to account for that if you want to compare the rate at which bacteria may or may not be transferred onto the Q-tips from different floor surfaces.

Good luck!