Homemade Petri Dishes Part 2: The Results

Well, I'm no bacteriologist.  But I think I see little globes of nastiness growing on the petri dish that we labeled "mouth".  This was the cotton swab wiped inside my son's mouth and then onto the petri dish. I used a butter knife to scrape off a hunk from the petri dish and put it on a slide with a slide cover, being very careful not to touch it. Truth is, you're not supposed to take the covers off of them after they've grown, but I couldn't get the entire dish to set on the stage of my microscope.  So I stuck my neck out for science, but you better believe I had plenty of antibacterial wipes and hand sanitizer close by.  The kids were NOT doing this part.  I then covered our specimen with plastic slide covers and set the microscope's magnification to 1200x .

Honestly, I don't have the energy to go through ALL of our 12 samples and compare them, so I'm not being very scientific here.  But the goal was achieved: we grew and observed nasty bacteria, right in our own school.  ICKY.  Into the trash they go!  Soap and water for EVERYONE!

I was actually pretty impressed with my little microscope on this experiment.  It's been a great tool to have in our school room.

Homemade Petri Dishes Part 1

On Mondays we do science together.  This is our second year trying to make our way through the Biology II: Worms, Beans, Germs, and Genes! Instructor's Guide (Noeo Science)
curriculum.  It's taking especially long because I keep interspersing it with Battle with the Bugs: An Imaginative Journey Through the Immune System.    Human Body Detectives  has several units actually, and I have mixed them all in at various points where they correspond with Noeo Biology II.
Today's lesson called for petri dishes.  Woops!  I only just read the lesson the night before and I don't normally have petri dishes on hand. So I started searching for a way to make my own.

I found a great site for homemade petri plates 
and I set out to make some! It was actually quite easy and turned out really well.  So glad that I never threw away that box of unflavored gelatin that's been in the cupboard over the fridge for soooooo long.

Here's what you need to get started

The instructions say to use foil muffin liners.  I had none!  So I experimented with several alternatives:

• normal paper muffin liners (I layered 3 of them)
• foil wrap pressed into the bottom of the muffin tin
• short, stiff, wax lined muffin holders.  I can't even remember where or why I got those. But they definitely worked the best!

The recipe made a full 4 cups, and I ended up with plenty left over. If I'd had more muffin tins and liners I would have made another batch.  Oh,I also used the container that held the muffin papers since it came with it's own lid. It also worked well. 

 What ever you use, make sure it's disposable. You don't want to have to deal with exposure to bacteria growth at any point.  You want something that can go straight in the trash.


I put each one inside of a plastic baggie and labeled it "________'s dirty hands" or "_______'s clean hands".  So there were two for each child. I put them on a cookie tray and stored them till morning in the fridge. I noticed that the thin paper muffin liners were sweeating at the bottom, so I put a folded napkin to absorb moisture under those.

The kids discovered this the next morning at when opening the fridge for breakfast.  So we wasted no time getting on with our experiment.  They each put their unwashed fingers in the "dirty" cup.  Some of them even went and touched the toilet first to make sure they were germ-ified.  Then we washed our hands really good, and touched the "clean" cup.  Now we wait!  We had a couple left over, so we swabbed the insides of our cheeks with q-tips and wiped them on the petri plates, just to see what happens.  We also placed a piece of pepperoni on another petri.  I wonder if/what it will grow?

We'll keep you posted!