CupofInsanity: What's the dirtiest place in your house?

Update: Video link added at the bottom.

Ever wondered just how dirty your house is? Like my wife, some of you probably don't want to know. But if you are going to clean your homes, should't we be able to quantify and measure the dirtiness of our environment? For this experiment, dirt is going to be bacteria/mold. In high school we ran an experiment where students sampled various parts of the high school and grew cultures in an agar solution. Samples were taken all over the place from door handles, bathrooms, to the break rooms microwave. Where were the most cultures found? The student break room microwave!

This project was also a great way for me and the kids to do a bit of biological sciences. Excited to see what germs grow around us? Let's get started!

Setup

I read about preparing agar and bacterial samples here. I bought some 60 mm petri dishes on Amazon. They appeared smaller than I expected when I opened them, but in the end they were the perfect size as I wanted to test a wide variety of samples.

Locations:
With help from the kids, we figured out a few places to check in the house. I did forget one control and that is a dish with any exposure.

Kitchen Sink-Control. Exposed to air for 30 minutes
Kitchen Sink-Swabbed around the cutting area
Kids Bathroom-Control. Exposed to air for 30 minutes
Kids Bathroom-Swabbed sink and bath faucet
Kids Bathroom-Shower floor and wall
Kids Bathroom-Toilet swabbed
Adult Bathroom-Control Exposed to air for 30 minutes
Adult Bathroom-Swabbed sink and faucet
Adult Bathroom-Shower floor and wall
Adult Bathroom-Toilet swabbed
Kids Bathroom-Swabbed sink and bath faucet -[Cleaned]
Kids Bathroom-Shower floor and wall - [Cleaned]
Kids Bathroom-Toilet swabbed - [Cleaned]
Adult Bathroom-Swabbed sink and faucet [Cleaned]
Adult Bathroom-Shower floor and wall [Cleaned]
Adult Bathroom-Toilet swabbed [Cleaned]
Door handle-Front door
Kids computer keyboard
Adult Bathroom-Shower floor and wall-UVC treatment for 40 minutes.

Procedure

We prepared the gelatin using the following recipe we found online. We multiplied the mixture by 6 for the increase in petri dishes. I had my daughter do the recipe translation so this was a great real life math exercise. It turns out that not enough gelatin was added. But more on that . . .

Bad recipe (gelatin liquefied at incubation temps0:

1 1/2 C Water [Drop to 1 C]
2.5 gelatin packets. [Up to 3 packets]
3 t of beef stock powder. Worked out to 6 cubes
6 t sugar

Mix and boil. From my gelatin experience I should have known to bloom the gelatin first in cold water and then add the slurry to the final hot mixture.

We ladled the mixture into 19 petri dishes and set them in the fridge to cool. After a few hours they were nice and solid.

Now the fun part begins. I had the kids look at the above list and start collecting samples by Q-Tips. My little army went out and diligently swabbed all the dirty parts they could find and rubbed it back into the gelatin mixture. I labeled and threw the samples in the incubator. We actually don't have a fancy incubator, so I placed them into the oven and left the oven light on. I know from my yogurt making that the oven runs around 95 Fahrenheit, so this should be good for bacteria.

The next part was up to me. I had to clean the bathrooms! Sharing how I cleaned in a following post. After I was done cleaning I went to check on the gelatin samples and was saddened to see that they had all liquified. :-(. I ended up not swabbing the clean bathroom samples, although in hindsight, I should have.

Results (well kind of)

We still left the samples in the oven for a day and a half. I was surprised to see some type of growth on the culture, although not as spectacular as I'd thought. Here are the results.

#	Room	Location	Control	Image
1	Kitchen Sink	Exposed to air for 30 minutes	Yes
2	Kitchen Sink	Swabbed around the cutting board area and sink
3	Kids Bathroom	Exposed to air for 30 minutes	Yes
4	Kids Bathroom	Swabbed sink and bath faucet
5	Kids Bathroom	Shower floor and wall
6	Kids Bathroom	Toilet swabbed
7	Adult Bathroom	Exposed to air for 30 minute	Yes
8	Adult Bathroom	Swabbed sink and faucet
9	Adult Bathroom	Shower floor and wall
10	Adult Bathroom	Toilet swabbed
11	Kids Bathroom	Swabbed sink and bath faucet -[Cleaned]		No samples taken
12	Kids Bathroom	Shower floor and wall - [Cleaned]		No samples taken
13	Kids Bathroom	Toilet swabbed - [Cleaned]		No samples taken
14	Adult Bathroom	Swabbed sink and faucet [Cleaned]		No samples taken
15	Adult Bathroom	Shower floor and wall [Cleaned]		No samples taken
16	Adult Bathroom	Toilet swabbed [Cleaned]		No samples taken
17	Door handle	Front door
18	Kids computer	Keyboard
19	Adult Bathroom	Shower floor and wall-UVC treatment for 40 minutes.

Some side by side comparisons

Kids (3) and Adult (7) bathroom control.

Kids (4) and Adult (8) sinks.

Kids (5) and Adult (9) Shower.

Kids (6) and Adults (10) toilets.

Densest growth. Adult sink (8) and Kids computer keyboard (18)

Conclusion

Despite the collapse of the gelatin medium, this did demonstrate that something is growing in here. The fact that it looked all the same troubled me. Perhaps they all some degree of the same air mold and that our practices were not very clean.

When looking at the pictures, the ones that appear the whitest had the most mold. The darker the petri dish, the easier you can see the black paper under the petri dish.

Some conclusions:

The dirtiest place? The bathroom sinks.
The cleanest place? The toilets-when compared to the control, the sink and shower.
The computer keyboard was also very dirty-but we all knew that right? (Better stop eating sandwiches when I type . . .)
The UVC lamp I made seemed to do an okay job. There is some slight bacterial growth when compared to the adult shower. I need to test this with a no exposure control to see if it is truly effective.

Ultimately, I we need to run this experiment again with proper medium. I might try agar or use a thicker gelatin recipe.

Let me know in the comments if there is anything else interesting you like to see tested!