Saturday, April 14, 2012


We've been doing a little experiment over the last couple weeks. Zaya got a bacteria growth kit for his birthday, and was very excited to begin collecting germs.
We prepared all our petri dishes first, which involved cooking up some germ-food. (Chicken stock and agar).

After letting them air dry...

We put them in the refrigerator to wait.

We collected germs around town while running errands. I even put them on my shopping list.

We sat them on the counter, and today I decided it was time to end the experiment. You can only have a stack of bacteria on your kitchen counter for so long before it starts to affect the family psyche. (They were under a towel, but I still knew they were there.)

The first six are about two weeks old, so some of those colonies (the creek water) have started to die away. Some, on the other hand, (the wal-mart cart handle) are still going disturbingly strong.

The last nine are just about a week old.

Here are the results. The picture first.

1. Spring Street park

2. Wal-mart cart handle

3. Door handle of the Wilkenson Drug Store

4. Coke puddle on McDonald's parking lot

5. Edge of McDonald's trashcan

6. McDonald's bathroom latch

7. Our backyard creek

8. Computer keyboard

9. Zaya's cough

10. Toilet ring

11. Fridge drain channel

12 Outside of raw egg shell

13. Miriam's finger trip

14. Washing machine ring

15. Top of soap bar in bathroom

As you can see from the picture, some of them were surprisingly germ-free. Notably the latch of the McDonald's bathroom stall, Zaya's cough, and the handle of the local pharmacy.

Some were distressingly active. i.e. the aforementioned Wal-mart cart handle, Mim's fingers, and the most surprising, which was the top of our soap bar in the bathroom. In fact, the germs that showed up on that one were different than any of the others. This was Safeguard soap, by the way, which is supposed to be anti-bacterial.

Another interesting thing to note...the large black germ colony from the Wal-mart cart handle looked exactly the colony from the toilet ring, and...wait for computer keyboard. Yes, it is hard to type with sterile gloves on.

We have five petri dishes left, and plan to collect for those this week. I will not be sorry to be finished with this experiment.


Lilibeth said...

That's one of those once in a life time endeavors. I remember doing something similar in home school when I was in third grade. We used jello for agar and got some impressive results. Is this experiment going to make the kids stop using soap?
I wonder what they'll tell the Wal-mart clerks next time they visit.

Chandelle said...

Very entertaining! I remember germ full petri dishes in science class. I'm glad you shared your results - thanks!

aftergrace said...

I remember doing this in Biology ! in highschool. My poor lab partner ended up getting a staph infection from his samples from the cafeteria. Wow, makes for a scary world in which we live!

Lainey-Paney said...

Love, love, love this type of stuff!

If you want to take it a step further: swab mouths. The same mouth for several petri dishes. Let the bacteria colonize. Then, take a small circle (size of a dime, for example) of a coffee filter soaked in mouth wash and place one in the center of each dish. After a few days, measure the circle around the mouthwash dot to see which one kills off bacteria better.

I LOVED doing this experiment for the science fair one year!