Countertop Experiment Procedure

This is my basic procedure that I use to test all cleaning products on my countertop.  I used masking tape to section off squares on my kitchen countertop and labeled them according to what I would be testing. I made sure that my countertop was very clean to start with, of course. 




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




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




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



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



I rubbed 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. 



After the allotted time, I used a sterile swab to swab the square. The squares were still wet after 5 minutes. I rubbed all over the square but I did not touch the tape (just in case the tape held onto bacteria and interfered with the experiment). 



Then I scribbled 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.


The plates were incubated for 24-48 hours in my homemade incubator consisting of a plastic box and a heat lamp. The temperature was 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 so 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 were 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. 



Understanding Agar Plates

In case you are new at looking at agar plates, let me explain. Agar is a Jello-like substance that bacteria and fungus like to grow on. The whitish/yellowish dots you see are colonies (or piles) of millions of bacteria. Some types of bacteria are not able to grow on these agar plates. Viruses can not grow on these agar plates. So, just because a plate looks clean, doesn't mean that no microorganisms whatsoever were present. We assume that a clean plate means that most bacteria were killed. However, there is the tiny possibility that the cleaning product just stopped the bacteria from growing as opposed to actually killing it. Also, I can't make any determination as to the time it took the product to kill the bacteria since the product was still with the bacteria on the agar plate. (Both the bacteria and the cleaner would be picked up in the sterile swab.) So, I don't know if it took 1 minute to kill the bacteria or hours. These experiments are still very useful when used to compare cleaning products and cleaning methods.