Introduction: Grow Bacteria From Gross Stuff!

Picture of Grow Bacteria From Gross Stuff!

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

Picture of 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

Picture of 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

Picture of 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!

Picture of 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

Picture of 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)

Picture of 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!


SHOE0007 (author)2016-12-05

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.

SHOE0007 (author)2016-12-05

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.

SHOE0007 (author)2016-12-04

Iron (II) sulfate - some bio film result.

Manganese sulfate - bio film.

SHOE0007 (author)2016-12-04

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

Copper (II) bromide - low bio film.

SHOE0007 made it! (author)2016-12-04

Here is 2.35% (Not 2% I just labeled it that to prevent errors with saving) of Hypobromic acid with glucose and soil. The pH rapidly drops sometimes by 0.4 unit of pH. Some bio films formed too.

SHOE0007 (author)2016-12-03

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!

SHOE0007 (author)2016-12-01

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.

SHOE0007 (author)2016-11-29

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.

SHOE0007 made it! (author)2016-11-29

Here is data on Potassium sulfurmic acid with Potassium acetate as a buffer. The slight reduction of pH but no bio film occurred may mean little resistance to this chemical.

SHOE0007 (author)2016-11-28

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

SHOE0007 made it! (author)2016-11-28

Here is a graph of 1.5 g of iron sulfate 7 hydrate with lactobacillius bacteria. No death of cells were recorded and a slight shift in pH down wards by 0.2-0.3 pH units per 24 hours was recorded. Also no bio film occurred. Perhaps the dose of iron sulfate was not high enough to kill or effect severely the bacteria! Here is the graph. An issue of tightness to prevent air from converting iron sulfate into iron (III) sulfate and rust may have been an issue too. It took 15 minutes with careful and quick opening of lids of containers to limit oxygen exposure.

SHOE0007 (author)2016-11-27

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

SHOE0007 (author)2016-11-27

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.

SHOE0007 (author)2016-11-27

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.

SHOE0007 (author)2016-11-27

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.

SHOE0007 (author)2016-11-26

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.


SHOE0007 (author)2016-11-26

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

SHOE0007 (author)2016-11-26

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??

SHOE0007 (author)2016-11-26

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).

SHOE0007 (author)2016-05-19

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.

SHOE0007 (author)2016-05-15

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.

SHOE0007 (author)2016-05-15


SHOE0007 (author)2016-05-15


SHOE0007 (author)2016-05-15

Here are some examples of molds absorbing 0.25% Malachite green solution which is still toxic. Here the Ma Green is broken down by the fungi. This fungi is safe but others may not be. (Do your own research before attempting this!!!)

SHOE0007 (author)2016-05-15

The Pencillium absorbs and traps the Iron EDTA sulfate solution into the spores so it would be safe for normal diposal. Only very harsh chemicals like 20% bleach in the landfill could in theory break the bonds and release the Iron EDTA. Extremely unlikely though.

SHOE0007 (author)2016-05-15

Here I am making iron EDTA sulfate salt solution with inositiol and sucrose as the medium with agar to allow Pencillium D to grow on.

SHOE0007 (author)2016-05-14

I decided to only use Iron ferro(II)cyanide salts and potassium ferrocyanide salts since they are the least toxic. Other molecules like Cobalt cobalt ferrocyanide and similar salts MAY release toxic cyanide gradually even if bio remediated and thus I will only test certain types.

SHOE0007 (author)2016-05-11

Again the slopes for both were 1 perfect indicating no effects on the bacteria and the disinfectants due to buffers see below and the fact the slope shift is constant.

SHOE0007 (author)2016-05-11

Here is some more data on Garlic vs sodium bisulfite solution. The garlic has citrate and sodium citrate buffers slowing down the reaction a bit. Sodium bicarbonate sodium bisulfite has a buffer properties too.

SHOE0007 (author)2016-05-11

EDTA reactions with very reactive metals (Manganese) could do more damage than EDTA copper. It is all to due with the reactivity of the EDTA and the metal. This data will eventually be shown with 0.5 moles EDTA with excess lye to make the pH 8.0!

SHOE0007 (author)2016-05-10

As long as there are trace of lye present for the equilibrium you will get iron as ions and as Fe(OH)2 solid as well. This would work with Cu+2, Mn+2, Ca+2, Zn+2, Ni+2, Mg+2, etc.

SHOE0007 (author)2016-05-10

Here is how EDTA works with lye and iron.

2*EDTA-Na(2)-1(aq) + Fe(OH)2 + 3 Na+ + 3OH-1 <> NaOH + 2EDTA-Na(3) + Fe+2 + OH-1 + OH-2.

SHOE0007 (author)2016-05-10

Oops I mean to say when the slope is abnormal it MAY lead to lower R2 values. Resistance to the chemcial is directly releated to the slope dropping below a specific value = 1.

SHOE0007 (author)2016-05-09

Here is graph of two more types of chemicals Gold acetate and cobalt ammonia chloride.

Here the cobalt salt is more toxic to the bacteria than the gold acetate. Thus the bacteria slope is slowed down.

SHOE0007 (author)2016-05-09

Here are two pictures of the graphs I made below. A lower R2 value doesnot mean error but less tolerance than some other types of graphs.

SHOE0007 (author)2016-05-09

Here is some data for squats and bacteria and sugars.

Quats 6 mg with acetic acid and sodium acetate with silicon

Time Hrs pH amp
by 62.5

0 4.0

24 3.9

48 3.7

72 3.6

96 3.5

Sugar (5 g glucose) plus 100 ml tap water (CONTROL) + 4 ml
bacteria through filter. + 1 g milk powder.

Time Hours pH
amplified by 62.5x

0 4.5

24 4.2

48 4.0

72 3.8

96 3.6

SHOE0007 (author)2016-05-09

This isn't advertizing just that the Phenol in the acid fast is very useful (for me) to identify the bacteria that was growing on two different types of soils (sterilized soil). However with Phenol at 4.55% you need to be very respectful with this chemical. It is also very unlike to find TB in steralized packaged soil!?

SHOE0007 (author)2016-01-14

Here is some data on 0.5 ml cobalt ammonia chloride in 5 g glucose, 5 g ox powder, 100 ml tap water, etc. 0.5 ml

Hours ph amplified by 2000. 20 mg cobalt ammonia chloride.

0 4.31

24 4.12

48 3.01

72 2.62

96 3.31

Here is the data for 4 ml or 280 mg cobalt ammonia chloride.


0 3.38

24 3.38

48 3.82

72 4.32

96 4.63

Joekevdv (author)2015-10-20

I always enjoy your Instructables! I used this one to sample bacteria from objects from a museum for an art project for school. I got caught while I was rubbing a q-tip on the surface of one of the art objects, haha. But the bacteria are growing pretty good!

SHOE0007 (author)2015-07-24

Here I talk about the min chlorine capable of killing bacteria 5 mg per L. Several more safer salts like Trichloro-S-Triazinetrione can be used to prevent mold and other fungi from growing on plates. A dosage of 3 to 3.5 mg per L chlorine (free) can be added just before you make plates after boiling has stopped due to lower heat. HOCl plus oxygen and boiling could make HClO3. Avoid by adding Trichloro-S-Triazinetrione after agar boils and starts to cool off. PLAY IT SAFE READ BELOW,

SHOE0007 (author)2015-07-22

Below is the recipe HOWEVER only grow from specific SOIL to be fairly safe. Make sure that the soil has been STERILIZED FIRST. Research the legatiy and the soil company past (like any issues with disease outbreaks from that soil) BEFORE doing!!! Otherwise it could be dangerous.

SHOE0007 (author)2015-07-22

Here is a fairly cheep way to grow any organism (though be extremely careful) with vitamin tablets, glucose, yeast extract and beef extract. Here is the vitamins and minerals that 100 ml would give you.

eef Ox Vitamin/Minearal Yeast Glucose agar.

for 100 ml

Grams Protien: 3 g.

Vitamin B1 = 0.75 g +0.0041 g = 0.754 g.

Vitamin B2 = 0.75 g +0.0046 g = 0.755 g.

Vitamin B3 = 1.5 g +0.016 g = 1.516 g.

Vitamin B12 = 0.5 g + 0.000021 g = 0.500021 g.

Folic acid = 1 g + 0.0004 g = 1.0004 g.

Biotin = 54 mcg. Trace.

Pantothenic acid= 12.5 mg.

Vitamin K3 = 25 mcg. Trace.

Sodium salt: 160 mg + 700 mg = 860 mg or 0.860 g salt.

Calcium carbonate = 0.3 g

Iodine (potasium iodide)= 0.015 mg.

Iron (iron fumarate) = 6 mg.

Manganese (II) sulfate = 5.5 mg.

Chronium (III) chloride = 35 mcg.

Selenium salt of sodium = 55 mcg.

Zinc oxide = 11 mg.

Fungi inhibitors ( Made by boiling 2 ml 1% bleach in 100 m tap water).

sodium chlorate = 0.008 g.

sodium hypochlorite = 0.0066 g.

SHOE0007 (author)2015-07-04

I have made agar like this and added protein mix from the store since it higher in protein. I another chemical that you could add is Phenol red as a indicator. If the bacteria can use the sugar then the bacteria will produce an acid turning the plate yellow. If the bacteria cannot use sugar but converts protein (amino acid) into ammonia the plate will go from orange-red to pink. I did this with Nutrient agar with sucrose and phenol red (1.5 ml of 0.02%). The phenol red acts as a way to easily tell if something is growing on the plate. Amazon and other supply companies sell phenol red at low concentration 0.02% with chemicals that reist bleaching from chlorine.

SHOE0007 (author)2015-07-01

Remember to check MSDS always before using any chemical or toxic gases or an explosion may be the result. Be careful.

SHOE0007 (author)2015-07-01

I have in the past taken bacteria from packaged soil and with many test for microbiology have determined what kind of bacteria it is. NEVER take a culture from pond water due to the risk of pathogens!! Cultured bacteria from packaged soil is screened first and samples are regularly taken so this makes it fairly safe to do. This is what my doctor told me when I discussed what I was doing. I did phenol red sugar broths, Methyl red test and much more. If it is ok to do it here then I guess there is no risk or very little risk.

I did Gram stain, Acid fast stain, Endospore stain, and Loafer Methylene blue stain as well. All these chemicals are dangerous so I always wair gloves and safety goggles with a rubber apron.

Tanmayg (author)2015-06-25

What if the bactera spreads and causes diseases? Take care while handling those dishes.

Hey Tanmayg!

It's a good thought to take precautions with things, but the things that grow here are pretty innocuous as they are seeded from things that are all around us anyways. It is a good thing always to take precautions with live cultures. No licking the plates when you're done! :)

Thank you much for the comment!

I can see it now,
"I'll give you $3 if you luck the plate"

rbessa (author)2015-06-26

Nice tutorial for introducing people to microbiology.

You should add an appendix on how to properly propagate desired colonies to other plates (under flame). And a few safety guidelines and disclaimers (just in case :p).

csorin1 (author)2015-06-26

hello again ! can i use pork gelatine instead of agar agar?

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