Countertop Experiment Procedure

Here is the basic procedure that I use to test the bacteria-killing power of various products on my countertop. First, I make sure my countertop is nice and clean. Then I used masking tape to section off squares on my kitchen countertop and labeled them according to what I would be testing. 



Next I make germy water. To do this I mix a small scoop of mud from our back yard into purified water. Then I pour the muddy water through a paper towel to filter out the chunks. I am left with very dirty water which contains lots of bacteria. For some experiments, I also scrape bacteria off of an already grown agar plate from a previous experiment and mix those germs in. This way my "germ water" has lots of bacteria in it. 



I put 1mL of germ water onto each countertop square with the exception of the "clean" control square using these 1mL syringes



I rub the germ water around the square with my gloved finger. Then I let the squares dry completely which takes 2-3 hours. 


Once the squares are dry, I put .5mL of each cleaning product onto its respective square. 


I rub the cleaning product around to completely cover the square using a clean gloved finger. I went over the square a few times to make sure that the cleaning product completely covered it. Then I set a timer and let the cleaning product sit on its square for 5 minutes (10 minutes for some experiments). 


After the allotted time, I used a sterile swab to swab the square. Most squares were still wet after 5 minutes. However, if a square is dry, I dip the swab in sterile water before I rub the square. I rub all over the square, but I do not touch the tape (just in case the tape holds onto bacteria and interferes with the experiment). 


Then I scribble all over an agar plate with the swab. 


If you want to do these experiments yourself, I used these agar plates available on amazon. They come with the sterile swabs.


Then I incubate the plates for 24 hours in my homemade incubator consisting of a plastic box and a heat lamp. The temperature is about 90 degrees F. In case you are repeating this, the plates need to be put into the incubator upside down. (That means that the agar is on top. This way condensation does not settle on the bacteria colonies.)  Any bacteria present on the plate will grow and multiply. After about 24 hours you can see colonies (or piles) of bacteria on the plates. It is important to remember that viruses do not grow on these plates. Just bacteria and some fungus. Also all types of bacteria do not grow on these plates. So, a clean looking plate does not necessarily mean that there are no microorganisms present. It just means that nothing that could grow on the agar plate was present. However, this is still a very valuable information for comparing different cleaning products. 



Now you are all ready to look at some of my experimental results. Go back to the main Cleaning Product testing page and click on the link to the product that you want to see. 
--Annie Pryor, Ph.D.