QUESTION: Does cleaning your kitchen every day result in a kitchen with less culturable organisms than a kitchen cleaned twice a week.
HYPOTHESIS: My hypothesis is that cleaning twice a week will result in less bacteria than cleaning every day. Or, that our house will be cleaner than my grandma’s. I believe this to be true because I think airborne contaminants and foot traffic will contaminate a kitchen as soon as you finish cleaning and make the extra cleaning a waste of time.
· latex Gloves
· Lysol Spray
· Isopropyl Alcohol
· Plastic Tub
· Two Clean Towels
· Heating Pad
· Agar Growth Medium
· 12 “ Ruler
· Petri Dishes
· 6” Sterile, Cotton Swabs
· Plastic Template
· Sharpie Pen
· Two spray bottles
· One container of Lysol Kitchen Spray
· A kitchen scale.
· Eight sterilized wash cloths and two sterilized sponges and two new mops.
The first step for my project was preparing an incubator for my samples to grow in. I used a plastic tub/tote that we sterilized with the streile setting on the dishwater and Lysol. Under the tub, I placed a towel, a heating pad, and another towel. I placed a thermometer in the tub to keep track of internal temperature. I kept the temperature between ninety and one-hundred degrees Fahrenheit.
Next, I used a kitchen scale to prepare identical bottles of kitchen cleaner. Each spray bottle had 8 oz of cleaning solution diluted with 1 oz of water. I sterilized two sponges in the dishwasher on a high heat setting and washed eight wash rags in a bleach and water cycle. After I removed the cleaning supplies, I used gloved hands to place them in plastic bags. Each home would use one wash cloth every two days, running through a normal wash cycle as they were used up. Sponges were used for the entire week and each home put them in the dishwasher after each cleaning day.
Next, I had to prepare Petri dishes with the agar growth medium. After the agar had cooled and hardened, the Petri dishes were ready for use. Before starting to collect samples, I sterilized all the areas where I would set my equipment during the experiment to reduce the chance of cross contamination. I took five samples from each kitchen and had three controls. One control was sealed immediately upon setting (to show if I messed up during making them). One was open to the air at my house and the other house to see if there was airborne contamination.
I took five swabs one from each surface per kitchen; 1” from the bottom, left corner of the sink edge, on the tile; the sink bottom (once inch from the disposal); the exact center of the stove top; the front of the refrigerator handle (two inches from the top); and the floor in front of the trashcan. To insure I got a similar sample size from each location, I used a plastic template.
When I swabbed the surfaces, I used a dry, sterile swab. I immediately put the swab onto the agar and made a snake-like motion over the medium. I, then, put the lid on the sample and taped it shut. I labeled the lids of the samples so we knew which sample was from where. I put the samples in the incubator and noted the time. All samples stayed in the incubator for seventy-two hours. I rotated them every twelve hours to make sure there was equal heat. Before removing my samples from the incubator, I prepared a sterile space for counting and had my sister and mom count as well to insure a consensus on our data. We eached use different colored Sharpies and wrote our numbers down without knowing the numbers the others reached. We wore gloves and masks during this process and we washed hands aggressively after completing the steps. After removing the Petri dishes, they were photgraphed and I counted the number of bacterial or viral colonies on each dish. Some colonies were too numerous to count. These are represented with the letters “TNC” on my data sheet. I also found mold that I didn’t expect and noted the presense of mold in my data. To double check our counting method, we calculate the surface area by measuring the big colonies to make sure our results were accurate.
RESEARCH: For this project, I had to research how to properly prepare a Petri dish with agar growth medium. I had to research the temperature that was best for optimal organic cell growth. I researched how to count colonies without a microscope. Before the project started, I researched the marketing data on common household cleaners to figure out which one I could use as an all purpose cleaner. I also kept a record of the homes cleaning methods; noting time spent, temperature of water used, and materials used. I also researched the correct way to sterilize equipment I was using and how to avoid cross contamination in kitchens.
(NOTE: I left out the bibliography because it's really long! - Pmomma)
INTERPRETATION OF DATA:
From looking at my data, it would appear that our kitchen (cleaned twice a week) had more organic organism growth than my grandma’s kitchen (cleaned every day). With the exception of the mold growth on her floor by her trashcan, her house had fewer colonies and TNCs. I think, however, that the mold on her floor might be a direct correlation to her daily cleanings since it may mean there’s more pooled, warm water sitting on her floor (which mold likes). In contrast, by only mopping twice a week, you give the floor, and surrounding cabinets and materials, a chance to dry all the way. From my data, I can see that the dirtiest place in both houses were the floor by the trashcan. The “cleanest” place, in the “every day house”, was the stove top. This might be due to the temperature of the stove top when being used: maybe it’s too hot for bacteria and viruses to live? The cleanest place in the “twice a week” house was the refrigerator handle. This surprised me! It’s interesting to note that the top three dirty places in each home were the same: in order; floor, sink tiles, sink bottom. My controls grew nothing – which means I was successful in keeping the experiment from cross contamination.
My conclusion is that my hypothesis was wrong: my grandma’s house (cleaned every day) resulted in less organism growth than my house (cleaned twice a week). My experiment was limited, though, by the fact that I didn’t know what bacteria or molds grew out in the samples. Knowing the type of bacteria that grew might show that grandma’s house had some bad bacteria. So, although we had more organisms in our house, they might have been safer for humans.
One of the variables I didn’t think about is the fact that my house has six people living in it and grandma’s house has two people. And, my house has four kids living in it and they’re all under 13 years. So, I think there’s more exposure to germs in my house. I could’ve solved this variable by using stand alone samples (tiles from a store or pieces of floor by the same trash can but cleaned differently). Another variable I didn’t foresee was that the homes used different approaches to hand washing. We use a lot of Purell in my house, which may have made the germs on the refridgerator handle less numerous because it's a rule that we have to wash our hands before opening the unit to get food out or put food away. My grandma's house doesn't have that rule. Another variable was the ambient temperatures of the homes. My grandma's house is kept colder than our house. That might have made a difference in how fast organisms grew.
I could re-work this project by removing the variables I talked about in my conclusion. I could eliminate the tests like the sink bottoms and redo the tests so that I use the same materials in the same environment, but clean them at different intervals. I could have two tiles and clean one every day and the other one twice a week. And, since they’re in the same house, we’d eliminate the exposure variable. I could also try to find a way to figure out what the colonies were. If I had the chance, I would want to do the project again and do it at different times of the year to see what effect the weather and humidity had on the tests. The project also made me want to see how using Purell and frequent handwashing effects the growth of organisms on house hold surfaces.