Grow Bacteria From Gross Stuff!




Introduction: Grow Bacteria From Gross Stuff!

About: The Oakland Toy Lab is a community-based wonder lab for students to build, tinker, explore, make, break, and learn! We are writing up engaging science experiences so that educators, parents, youth, and famil...

Ever had that hankering to grow millions of something? With a little swab from the inside of your mouth or the back of a toilet seat, you'll have a veritable bacteria farm empire in no time at all. Ever wanted to prove that a dog's mouth is cleaner than Ted from accounting's desk? Now is the time to do it with science!

Making agar agar plates for bacteria is a great way to (1) Grow and learn about the microorganisms and cultures for sprouting young biologists (read: students!), (2) Get to practice some kitchen chemistry, (3) Prove that the world is just as gross (and awesome!) as you thought it was, and (4) You get to say "agar agar" lots!

Let's make a bacteria farm!

  • What: Growing Bacteria From Gross Stuff
  • Concepts: biology, microbiology, cell life, bacteria, fungi
  • Materials:
    • Petri dishes (top and bottom)
    • Q-tips
    • White sugar
    • Bouillon Cubes (available at any most groceries)
    • Agar Agar (East Asian grocery stores, also some large general ones)
    • Measuring Cup
  • Tools:
    • Stove or way to boil water

Let's dive in and get cultured!

Step 1: Mark Your Dish

Start off easy by dividing your petri dish in to several quadrants where we'll test different swabs. Write on the bottom of petri dish in Sharpie. I chose to do symbols so I could make a key and didn't have to write backwards, as we'll mostly be viewing it from the other side.

Step 2: The Bacteria Food Mix

Time to make something the bacteria culture we'll be talking about for weeks!

None of this recipe has to be exact, but here are good ratios to start with. For a small recipe (about 4 plates), start off with boiling ~ 200mL of water. You want to get it truly hot hot hot. Mix in the teaspoons of agar agar, stirring to make sure it dissolves completely. This is super important in making it gel later. Then add in your sugar (for easy bacteria carbs) and bouillon (for bacteria protein), and mix it all together.

IMPORTANT NOTE: The agar agar really needs to dissolve completely, otherwise you end up with pudding at the end. We're going for a tough gel. If you need, you can mix all of this on a stovetop while the water is boiling to ensure it reaches that high temperature necessary.

Step 3: Pour and Refrigerate

Pour your food mix into the bottom of your petri dish so it is about 1/4" or so deep. Place the lid back on to avoid contaminations, and then place them in the fridge to make the cooling go faster. Leaving them at room temperature is okay, too, it will just go slower.

Step 4: Swab the Decks!

Time to get gross! Start with writing a key as to what the different cultures are in your bacteria farm. I chose to do my mouth, a dog's mouth (thank you Cloude!), the kitchen top, and a toilet. I truly have no idea which will be the dirtiest.

For each one, use a fresh Q-tip, swab as best as you can, and then rub it on the gel in the corresponding quadrant of your bacteria plate. Make sure to replace the lid each time to minimize contact with the air around (there's a lot of stuff floating around).

If you're looking for swabbing ideas, here are a couple other ones:

  • Mouths before and after using mouthwash
  • Surfaces before and after cleaning
  • Compost Bins
  • Trash Cans
  • Doorknobs
  • Hands before and after washing
  • Ted from accounting
  • Armpits
  • Ted from accounting's armpits

Step 5: Replace Lid and Tape

Cap your petri dish and you can add some tape to keep the lid on while we wait for our bacteria colonies to grow. Keep in a warm environment for maximum growing potential, try to leave it relatively undisturbed. Oh, I can't wait to see what grows!

Step 6: Bacteria TA-DAAAA!!!! (and More)

After only a couple of days, colonies will start to grow and grow and grow. It's fun to watch the progress of a colony take off, and you can get some phenomenal colors and structures. In any given swab, you may get bacteria, fungi, or molds (a type of fungi), all of which have an amazingly diverse set of characteristics. They might be round, irregular, fuzzy, bright, or dull. Here's a great starting guide to interpret what you've found!

This is from five days after, and it looks like our toilet seat had some mold spores that are now growing like crazy in the to left quadrant. As for dog mouth vs. human mouth, I'll call it a tie! And the kitchen counter looks all right!

If you look really close at your colonies, you can see how they grew and the amazing shapes that they take as they interact with one another. It's a great thing to sketch and photograph over time, as your mini-farm empire grows. Interesting things to follow up with are the FDA's factors for microbial growth, this starter on bacteria multiplication, and looking at the history of understanding microorganisms.

Try this with classes! Try changing the recipe, the swabbing, the time, the temperature, everything! Your world is a science experiment waiting to happen. Have fun, and keep exploring.

Let me what you grow!

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53 Discussions

Fungi and bacteria varation plates.

Mold Ma Green Pic2.jpgMold Ma Green Pic1.jpgMal Green agar lactose inostiol sugar plates.jpgDSCF0815.JPGDSCF0693.JPG

Here is a graph of Manganese sulfate with some bio films forming near day 5. Also some of the MnSO4 was absorbed by soil and some of the acid (lactic acid) was absorbed by bio film and soil.


Here is iodine levels in ethanol I3- at concentrations of 25 mg per 200 ml tap water. No bio film results indiciating the bacteria was not stressed enough to have any effect. Will increase levels to 100-200 mg iodine.


Iron (II) sulfate - some bio film result.

Manganese sulfate - bio film.

Cobalt (II) thiosulfate in baking soda- some biofilm.

Copper (II) bromide - low bio film.

Here are some herbs that I retested but did use pH just oberved bio film and smell.

Garlic 5 days Stinky smell some bio film.

Ginger 5 days Stinky lot of bio film.

Mustard 5 days Stinky some bio film.

Cinnamon 5 days some what stinky, Some bio film.

Onion 5 days stinky bio film.

Tolerence of the graph was often near 1. With bio films formed for garlic and etc it proved that some did kill or stress out the bacteria!

I have been thinking....

I have recently tested cobalt chloride salt 10 g per 250 ml tap water with 5 g glucose and 4 g soil. The pH drop was a constant 0.2-0.3. The water used was fresh tap water stored in a jug closed to prevent change in CO2 levels in the water. R2 was 1.

Another important issue is for resistance is Bio-films. Alone a graph cannot tell you much but with the formation of bio films you can. All of these bio films happened in 5 days.

Cobalt (II) chloride 10 g per 250 ml Bio film.

Calcium (II) chloride 2.6 g per 250 ml No bio film.

Copper (II) chloride X g per 250 ml No bio film.

Tree tea oil 5 g in 250 ml No bio film.

Pine oil 5 g in 250 ml. Some bio film.

About the iron sulfate graph it also could have been that the bacteria grew and consumed iron ions but did not produce any Hydrogen sulfide. No black prepripate of FeS occurred.

Soon I will be recording data on salts of sulfumic acid (Potassium) with potassium acetate as a buffer.

I will also be testing just regular sodium dichloroisocyanurate at 0.1%.

Bromine from Potassium bromide mixed with sodium dichloroisocyanurate salt produces a lot of HOBr with a pH of 6.0-7.0! Wait a week for the chemical to come and I will be making a 2% stock solution. It must be near 0.1% or less when passing through the filter.

Here is more data on Tree tea oil with a low solublitiy in water. About 2 g of tree tea oil in 100 ml of tap water was added. Here a graph. A formation of bio film and the fact that the solution was not soluble in water gives a high resistantance to the chemical.


Here is data (Graph) on cobalt thiosulfate. Most of it has been neutralized with soda since I used sodium metabisulfite as a starting agent. No sudden drop in pH ment little Co ions attacked the cell.


Here is a link to lactobacillius bacteria and bio films. 40% of lactobacillius resisted QAC. The biofilm when stressed may act to protect this friendly type of bacteria.


Chloroxylene is condsiered a broad spectrum disinfectiant so it may not provide complete resistant to lactobacillius type bacteria.

Pine oil and chloroxylene are reactive to many bacteria but maybe this bacteria (lactobacillius R) is sort of tolerant to the dose of this chemical??

Here is what happened with a graph when I added 8 g of pine oil with chloroxylene to 100 ml of tap water with 5 g glucose and 4 g soil (bacteria sample).


Here is a graph of mint concentrations of menthol: 89.5 mg, menthone: 51.6 mg, etc. It is fresh mint boiled in water for several hours until it reaches 100 ml then 4 ml of solution is added to a graduated flask measured up to 250 ml. Each filtered solution is recorded up to 96 hours.

Mint filter graph.jpg

Here are some graphs on Tarragon and Mustard as you can tell Tarragon has less of an R2 value then Mustard. This may mean that Tarragon at these concentrations boiled has a greater antimicrobal effect on the lactobacillius bacteria.

Tarragon and mustard comparison.jpg