A few years ago, one of my kiddo’s classmates returned to school after battling cancer. As this classmate returned, the staff and kids did their best to keep things clean and germ-free. The concept of germs got them thinking about how they’re spread and how they can make people sick. It was the further discussion that ultimately morphed these questions into an experiment and a cool science fair project! Below, we’ll run through how our kids tried to find the germiest place in school. Feel free to use this guide if you’re curious or looking for an idea for your own science fair project… let’s science!
Overview:
SHORT VERSION OF THE EXPERIMENT (tl;dr): you will check for “germs” in different places around a school to see which surfaces grow the most bacteria. Not a scientist? NO access to a lab? NO PROBLEM! We will use materials you can find around the house, at the dollar store and of course Amazon. This is a great experiment for third graders and up, to teach them about how bacteria grow, setting up an experiment and the scientific method. Basic data analysis (counting, comparing) will be used and if you snap some pictures along the way, setting up a project board for the science fair can be done in super easy fashion!
Update: If you’re struggling to get started on a science fair project, check out our science fair project guide which details the entire process from start to finish (including HOW to find an idea). This “germiest spot in school” experiment follows the same steps described there.
Science fair project overview: what we’ll do
Streaking bacterial plates – how we grow bacteria
Bacteria are single-celled organisms… that means one cell = one bacteria. And because they’re so small, we can’t see them when we look at a surface unless we are looking with a microscope. So, how can we figure out which spot is the germiest? Bacteria grow incredibly fast compared to an animal or human, and we can use this to our advantage… we can sample or test different locations, let the bacteria from the different spots grow until we can see them, count them, and compare the different samples.
Sounds great! You might be thinking…how do we do that? By using a routine lab technique known as streaking bacteria samples on agar plates to grow bacteria. Take a look at this picture….
The material inside the petri dishes contains “food” for the bacteria (Luria broth in our case) which is in a semi-solid state (feels kind of squishy). Under the right conditions, bacteria can grow into colonies.
Once we INCUBATE the plates for a certain amount of time, and have colonies on our plates, we can count the number of colonies on each plate and make a comparison to figure out what is the germiest spot.
The video clip below shows you how we will “streak” the plates.
And just in case the video didn’t work or you don’t have time, here’s a diagram for how we’ll be streaking our bacterial plates. If you’re using this project as part of a science fair project, feel free to print out the picture and use it on the board!
Who can do this science fair project? Age range: 3rd Grade and up
We first did this science project with 2nd graders and while it worked, it would probably be better suited for 3rd-4th graders and beyond. Why? Biggest reason is the delayed gratification. In other words, this is an experiment where you will incubate plates and won’t get immediate feedback.
Materials – what you’ll need:
- 10-20 Luria broth (LB) agar plates (100x15mm) – sterile; the number of plates will determine how many spots you can test. You can use 1 or more plates per spot…using 2 plates per spot might be helpful to make sure the swabbing was done correctly. More on where to find these in a minute…
- 10-20 sterile wrapped cotton swabs – these will be used to “sample” a surface or area. I found these swabs on Amazon, but a local pharmacy/medical supply store down the street had them on sale.
- Hand sanitizer – for keeping hands clean.
- One bottle of water (unopened) – will be used to get swabs wet/damp before swiping an area.
- Pen/pencil and paper/notebook – for writing results
- Sharpie marker – for labeling plates
- Disposable foil roasting pan – this can be used to incubate/store the plates
- Heating pad – will be placed on top of the plates in the roasting pan
Designing the Experiment: picking a hypothesis
Remember, a hypothesis is a “guess” about what we think the answer might be… At this point, our main question that we are thinking about is the germiest spot in school.
- Any places leap out that might be the germiest?
- Are there certain areas you think might be “germ free”?
Now that we have a hypothesis, we need to think about how we are going to test our guess.
- How will the place you hypothesized compare to other locations in the school?
- What are some other places that you will test to determine if you are correct?
*Question to pose to get the students thinking before they start: how do you think “germs” travel?
Experimental controls
At this point, we’ll also want to pick out some “controls” to include in our experiment (QUICK question for the kiddos: why is this important? A: to make sure our experiment is testing what we think it’s testing). We need a POSITIVE and a NEGATIVE control plate. A good NEGATIVE control will not grow any bacteria while a good POSITIVE control will be full of bacteria. What would be something that is full of germs that we can swab? Any ideas?
CHECKPOINT: At this point, we should have a list of spots we’re going to test AND a hypothesis AND some controls. Make sure you have written this all down in the notebook. Here’s what our list included when the kids did their science project:
- Hypothesis: boy’s bathroom will be germiest spot (I believe the rationale was that boys can be a bit dirty or something along those lines)
- Locations to test: various desks in classroom, teacher’s desk, boy’s bathroom, girl’s bathroom, nurse’s office, lunchroom table, gym stage, drinking fountain
- Positive control: palm print on plate – press hand down on agar plate before using hand sanitizer
- Negative control: closed plate/don’t open/don’t touch
Your list should look something like this…
| Plate Number | Location | Colonies | Comments |
|---|---|---|---|
| 1 | Mr. Smith's desk | ||
| 2 | Positive control | ||
| 3 | Negative control | ||
| 4 | Stapler on Mr. Smith's desk |
Additional tips before you start…
Optional – homemade incubator…
The plates will need to incubate for about a day after you have streaked them with the samples from school. If you don’t have a spare incubator lying around (nope. we didn’t), you can still make one at home that will do just fine.
- Grab a tinfoil/aluminum roaster pan like this at a grocery or dollar store that will fit your plates.
- Place the plates in the roasting pan INVERTED (lid side on bottom/agar on top). You want to avoid condensation from forming on the agar surface.
- Next, cover the plates with a heating pad and use a few hand towels to keep the heat in.
- You may need to rotate the top plates with the bottom ones to make sure they are evenly growing. More on incubating plates in a bit…
Great detail…but where do I get plates? Two options: make them or purchase them.
Pouring the plates yourself (aka making them from scratch) is one option and here’s a home brew recipe you can use. I would STRONGLY consider buying them. Here’s why – if this is your first time pouring plates there is a strong chance you will end up with contaminated plates since these need to be made in a sterile manner. It’s more of a quality control issue rather than anything else.
When we did this science project, we did a side-by-side comparison with a set of plates made in my old lab (thanks guys!) as well as plates purchased from EZ BioResearch via Amazon. The purchased plates arrived one day later than we expected, but otherwise worked great. We had no contamination issues and both the lab plates and EZ BioResearch plates successfully grew bacteria.
Methods/Procedure – How we’re going to complete our science fair project:
The steps listed below are how we completed our germiest spot experiment as a science fair project. You should be able to do the same for your project. While we haven’t included the finished science fair project board for you, there should be enough info to make your own. In terms of how long this will take you from start to finish, there’s about 30 minutes of setup/prep time (assuming you are buying the plates), about 30 minutes for sampling and streaking plates and about 15-30 minutes to count plates/analyze. Incubation time is ~1-2 days (mostly hands-off time).
Setting up your materials
Alright… now that we have a hypothesis in hand and our experimental design set up, we are ready to get streaking! Are you excited yet??? Remember, you should have a list of spots you’re going to test and all your other materials ready to go (e.g. plates, swabs, etc.). Make sure you LABEL each of the plates…on the bottom, write a little number in Sharpie (“1”). You will want to know which number corresponds to which spot you are testing — keep track of this in your table.
Swab surfaces
Remember it’s important to avoid touching the tips of the swabs that will contact surfaces. Also avoid touching the inside of the agar plates. You want to prevent accidental contamination of the plates and getting a wrong or incorrect answer.
- To swab (or sample) the surfaces, open the bottle of water. Unwrap a swab and get the cotton part wet in the water.
- Now, rub the surface with the wet swab to make sure you’re getting a good sample of what’s on the surface.
- Next, open a petri dish and streak the swab over the plate. When finished, put the lid back on the dish and turn upside down. All the plates will be stored upside down so moisture doesn’t accumulate on the media.
- Next, if you haven’t already marked the plate with a number, use the sharpie to describe the spot you tested along the bottom edge of the plate — example: bathroom sink. Record this in your table in your notebook (example: #1 — bathroom sink).
- Repeat for each location you are testing.
- Positive control. Make sure you do a positive control for at least one plate to make sure the plates are growing bacteria.
- Negative control. Hold one plate back as a negative control (we DON’T want to see anything growing on this plate).
Incubate the plates
Now, on to the waiting! 🙂
While our bacteria have food, they also need a nice warm spot to grow. Incubate the plates for about a day. If you are doing the homemade incubator as described above, it may be like ~24-36 hours in the incubator. The pictures here show our very own incubator in action. The blue heating pad is set to a low temperature to keep the plates warm.
Rotate plates 1-2x, moving the top plates to the bottom. Make sure the plates are incubated upside down….lid on the bottom. This prevents moisture from accumulating on the agar. You should not need to open the lids any more. As the plates are incubating, you will start to see little “dots” growing on the plates….these are your bacterial colonies….if you see the dots, SUCCESS!!
Data Analysis – what does the data tell us?
Congratulations! If you’ve made it this far, you’re science fair project has worked and we’re about to find the GERMIEST place in school! YAYYY!!! Sort of.
The plates should be finished incubating and you should see colonies appearing on the agar. Keep the plates closed up – we used tape on the edge – to make sure kids don’t open them or try to touch the bacteria at this point. You can take pictures of the plates too in case your notes aren’t clear…here is a shot of two of our plates. These make for a great addition to any science fair project board!! The little dots on the plate are the bacterial colonies growing from the spot we tested.
You will also need to get out your notebook and the table that you created to track where each plate came from or what sample you were testing. The bacteria may not form distinct colonies (or circles) and may look more like a lawn of growth. This happened to a few of our plates. No biggie! Our kids quantified as best they could and if a plate was impossible to read, they labeled it like “ALL OVER”, “BLOB” or “++++”.
Keeping the plates upside down on a table, it’s time to add ‘em up! On your sheet with locations, write down how many colonies there were on each plate. Also include any comments/observations about how the plates looked. Once you’re finished, you can dispose of the plates in the garbage (won’t need them anymore). The data table with results should look something like the one below.
| Plate Number | Location | Colonies | Comments |
|---|---|---|---|
| 1 | Mr. Smith's desk | 0 | Was really clean!! |
| 2 | Positive control | ALL OVER | We pressed Sally's hand on top of the agar |
| 3 | Negative control | 0 | Nothing! we never opened the lid |
| 4 | Stapler on Mr. Smith's desk | 22 | Colonies are small, little white/yellow circles. they are sitting next to each other. |
So, was your hypothesis correct?
- Which plate had the MOST bacterial growth?
- Which had the least?
- Were you surprised?
- If students did replicate plates – sampled the same spot on two or three different plates – did the replicate plates give the same answer? What is the AVERAGE for this spot?
Conclusions: what we learned from our science fair project? Did it work???
Hopefully by now the kiddos have plate counts in hand and have charted out how the results compare to their initial hypotheses.
- What was the germiest spot? Can you explain WHY?
- Did your controls work? Is the negative control still negative? Did the positive control grow a lot of bacteria? If these didn’t, what do you think went wrong?
- What does this mean for the rest of the results — what can you say about it?
In our case, we were shocked to find out my kiddo’s desk was among the germiest spots (EEK!). What gives?? It wasn’t until after I decided to bring in roughly a case of extra Lysol wipes to the classroom, that we finally came up with an explanation.
Her desk was located right near the door and as students returned from recess her teacher and I noticed ~90% of her classmates brushed their hands on her desk or touched the top….high-traffic germ transfer in action. Two other spots we swabbed in the classroom were lower-traffic areas (like a corner) and had lower growth.
Separately, we were surprised to see growth from an object in the nurse’s office.
Next steps
For our kiddos, we didn’t do any follow-up experiments but we all washed our hands a LOT more often! Possible next steps/projects you could explore for a future science fair project:
- What kinds of bacteria are you growing?
- Does the growth change during different seasons?
- Do you think it would be better/worse during winter?
- Are there differences between schools? How would a high school compare to a grade school?
Lot of possibilities here – see what your kiddos think! Overall, this science fair project is impressive and interesting, and doesn’t take a ton of time. Best of all, it also exposes kids to the scientific method. Enjoy!
Resources:
- Publication from Microbiome from researchers at the University of Oregon on different types of microbes, or bacteria, in classrooms
- Link to our PDF version of this experiment
STEMomma is a mother & former scientist/educator. She loves to find creative, fun ways to help engage kids in the STEM fields (science, technology, engineering and math). When she’s not busy in meetings or carpooling kids, she loves spending time with the family and dreaming up new experiments or games they can try in the backyard.
