Thursday, February 14, 2008

By request...Jake's project.

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
· Thermometer
· Agar Growth Medium
· 12 “ Ruler
· Petri Dishes
· 6” Sterile, Cotton Swabs
· Plastic Template
· Sharpie Pen
· Tape
· 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)

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.


Michael said...

Wow! I'm impressed! How old is P2? I'm frankly not certain I could design an experiment with such rigor. As to his misfortune, that really is terrible since this was such a well executed project.
Incredible compliments to him, and incredible compliments to you for doing such a great job!

Milo Johnson said...

I'm a college science professor, and I'd be surprised if one in ten of my students could turn in work of that quality. Bravissimo!

Alison said...


That's a great project; bravo to P2 for conceiving and executing it! I'm so sorry about the science fair, though.


Berlzebub said...

That was really good. Especially the explanations he gave at the end of what he could change, and why. Very well done, Jake.

Maybe next year, he can do an experiment on the "clairvoyant coordinators". Just a thought.

PipesUp said...

Hi P-Momma,

Great job, P2. I'm ultra-impressed that a young fellow in primary school(?) put what was obviously so much effort, care and thought into his project.

Like berlzebub, I was particularly interested in the fact that, when the results didn't match his hypothesis, he reconsidered his initial idea. (Note to xtians: he *didn't* claim that Satan messed with his data.)

PM, you have smart kids to be proud of!

Paul said...

[Silentsanta, NZ]

Fantastic work, Jake. Very thorough, and most importantly, aware of lots of different things that could cause you to draw false conclusions.

Your mother may have taught you this one already:
"Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and [the second is that] you are the easiest person to fool."
-Richard Feynman

I have about 5 years of university study in various sciences; and too many students seem more concerned with dressing up their writing using impressively long words, instead of understanding what science actually is and how to go about it.

I think that you have created an excellent science project that shows a strong appreciation for what science is, and you should be very proud.

Matt D. said...

Hypothesis: Science fairs serve as the perfect growth medium for the "culture of fear"

Procedures: Conduct a science experiment that attempts to quantify the effectiveness of cleaning methods with respect to household bacteria. Submit the results of this experiment to the local science fair. Wait for disqualification due to fear...

I can understand their concerns about what sort of experiments are permitted and what sort of safety requirements must be followed - but the goal here is to educate and inspire an interest in science. The time to DQ a project is before it begins. Once it has already been approved, submitted, judged and's too late.

They should allow Jake's project to be included in the fair. Not only because it's unfair to punish him for the mistakes of others, but because it gives the administrators the opportunity to discuss safety rules, potential risks and why certain policies are in place.

They may have some legitimate concerns and there may be good reasons for sticking to their guns...but I don't see that there's sufficient justification to disqualify a project that could have easily been performed within the required guidelines, if only they had been clearly conveyed to the student.

Great job, Jake. Take comfort in knowing that you did a proper experiment, you learned something from the data and you aren't to blame for the confusion over the rules. Don't let one setback stop you from continuing to investigate everything about the world we live in.


Knitterman said...

Bravo to Jake! Boo to the stupid rule-makers making up rules after-the-fact and not ensuring every participant had the most current rules. Sheesh. Makes me wonder if that petri-dish provider was also a funding sponsor or advertiser for the Science Fair, which would be a serious conflict of interest issue. But never mind that.

The project was an amazing learning experience on so many levels, and what you learned cannot be taken away by anyone for any reason. Keep at it.

Bill said...

Excellent research, in any context.

Kitchen Scale said...

This is pretty good work. I'm impressed with the results. My mom cleaned every day and I didn't get sick near as much then as I do now! Great work. Now I know why.