Growing Bacteria in Agar Activity with Free Lesson Printable
The ever-popular growing bacteria in agar activity is eye-opening, fascinating, and well, kind of disgusting! But it’s an activity I highly recommend for all ages. There is much to learn!
We used this kit which comes with the agar already pre-made and in petri (pitri) dishes and includes swabs. You will want to gather extra swabs and disposable gloves.
(High school content for this activity is in a separate document from the lesson printable. Both request forms are at the bottom of this post. The information in the PDF goes into more detail about bateria, antiseptics, and disinfectants. )
Not wearing shoes in the house is a big pet peeve of mine, and despite the kind reminder on the garage door mat, shoes still make it into our house sometimes. So, since we had the bacteria growing kit, we decided to end the great debate – “How much bacteria comes in on the bottom of shoes?”
We have put together a detailed lesson and printable. Some of the information may be above your child’s grade level, and some of the pages in the printable are geared towards the youngest scientists.
You will want to also check out our other printable on germs and the immune system. If you have elementary-age children, use this agar activity and printable with the germ printable. You may also want to check out this make-a-mold-terrarium activity too.
My advice is to download the printable and use what works for your homeschool or classroom. Regardless of grade level, everyone will have fun swabbing different surfaces and watching the results grow!
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Table of Contents
Growing Bacteria in Agar Petri Dishes- What Is Microbiology?
Let’s review some microbiology background before we start growing bacteria in agar.
When most people think of the word “biology,” they think about all the amazing living beings they have seen. from the magnificent matriarchal herds of elephants to the gentle sea turtles floating through our oceans’ currents, even down to the humble dandelions that brighten up city sidewalks.
But biology is the study of all living things, and not all living things can be seen, at least with the naked eye. That’s right, there is a whole society of organisms living right under our noses – literally!
The study of these incredibly small living organisms is composed of two words, micro meaning “small” and biology meaning “the study of living things. So. this means that microbiology is the study of small living things, and that is exactly what we will be talking about in this lesson.
Salmonella bacteria under an electron microscope.
Actinomycetes bacteria under an electron microscope.
Why Study the Small Stuff & Grow Bacteria in Agar?
There are many reasons to study microbial life, both the good and the bad.
Pathogenic organisms, organisms like bacteria, viruses, cysts that cause diseases such as meningitis or tetanus, are some of the most famous microbes. We have to study them in order to understand the course of their infection, what medicines they are vulnerable to, and how they may be transmitted throughout human societies.
But, while many people believe bacteria and other microbes to be dangerous, gross, and overall undesirable, we actually cannot live without them.
There is an unending list of benefits that they provide for other living organisms, including humans, elephants, sea turtles, and even dandelions stuck in sidewalks.
Reasons Why We Study Bacteria and Microbes
Some of the reasons we study bacteria and microbes include:
- Food production and safety: Microbes are involved in food fermentation and preservation. Understanding their role helps in improving food production processes and ensuring food safety.
- Microbes can be both beneficial and harmful to human health. Studying them helps in developing treatments for infectious diseases and understanding the role of the microbiome in overall well-being.
- Many diseases are caused by or associated with microorganisms. Researching microbial life is essential for developing strategies to prevent, treat, and control infectious diseases.
- Microbes are used in various biotechnological processes, such as producing antibiotics, enzymes, and biofuels.
- Microorganisms are key in nutrient cycling, soil fertility, and waste decomposition. Understanding their functions is vital for assessing and managing environmental impact.
- Microbes are essential for maintaining ecological balance. They influence the growth of plants, the cycling of nutrients, and overall ecosystem health.
What is Agar?
Agar is a polysaccharide (puh-awl-ee-sac-uh-ride), which is a long, fancy way to say a big sugar molecule. This sugar is obtained from algae, and humans often use it as a thickening agent in many soups, preserves, and desserts.
When dealing with microbial life in any sort of laboratory setting, scientists have to provide microbes with plenty of nutrients and space to safely grow, without risk of contamination or infection.
Agar in powder form
Many microbes are grown in nutritional broths inside test tubes, but broths can be hard to store for long periods of time. Also, they don’t allow scientists to observe the colony characteristics of bacteria, which can be really important for diagnosis and research.
To combat the issues of broth cultures, scientists will add uncultured broth and agar to either a tube or a plate, with the agar acting as a thickening agent for the broth. Tubes are best for long-term storage and allow for greater specimen storage space. However, plates are best for observation and testing.
Slant cultures of Tricophyton mentagrophytes growing on Sabourard’s agar. Photo credit: Shutterstock
There are many different kinds of agar plates. Some can be selective for or against specific bacterial traits; others may help scientists differentiate between different kinds of bacteria based on their chemical characteristics. However, some agar plates may just be enriched, meaning they don’t select or differentiate, they just provide nutrients for microbes to grow. When we are growing bacteria in agar in this experiment, we will be using LB-enriched agar plates.
Experimental Purpose of Growing Bacteria in Agar
As stated previously, there are microscopic organisms right underneath our noses. They’re also in our noses, under our fingernails, and if you have ever heard the term gut flora, that is not referring to plants that grow in your belly. Rather, it refers to the billions of microbes that have lived and developed in our intestines.
However, microbes are not found only in or on our bodies, they are found everywhere, even in places that no other organisms can even dream of living. There are entire classifications of organisms called extremophiles that live and thrive in extreme environments. For example, the organisms that live in hot springs and deep-sea hydrothermal vents are known as thermophiles. Check our resource section below for more information about extremophiles.
Thermal pools at Norris Geyser Basin, Yellowstone National Park.
In this experiment we will be growing bacteria in agar as we explore how common and numerous microbes are in our daily lives by swabbing everyday places. To do this, we will be using pre-poured agar plates, sterile cotton swabs, and our creativity to think of the oddest places where nothing except microbes could ever live in our environment.
Did you know? Scientists have isolated many of the enzymes that extremophiles, particularly thermophiles, use to survive harsh conditions.
One of the most important enzymes for life is DNA polymerase, which is an enzyme that synthesizes new DNA strands off of template strands. Scientists can use the DNA polymerase from thermophiles to synthesize entirely new and isolated DNA strands from just one sample. This technique is called Polymerase Chain Reactions (PCR) and is foundational to ancestry testing, molecular forensics, and the diagnosis of genetic diseases.
What Will You Swab – Growing Bacteria in Agar
Before getting started with growing bacteria in agar, think about what you are going to swab.
In addition to testing different surfaces (ie, kitchen counter, cell phone, steering wheel, toilet handle, etc.), think about how you can test a surface before spraying it with disinfectant and after spraying it with disinfectant. When we tested disinfectant, we swabbed 1/2 of the agar with disinfectant. Once the top is back on the petri dish, draw a line down the middle and use the marker to indicate which side has disinfectant and which does not.
Additional ideas for growing bacteria in agar:
- •Swabbing a hand before washing with soap and then after.
- •Swabbing a scalp. Wipe one-half of the agar with disinfectant and leave the other side untreated. Then, take two swabs of a scalp. Transfer one swabbing to one half of the dish and a second swab to the other half of the petri dish.
- •Swab your gum line in your mouth and place it on one half of the petri dish. Then, use a mouthwash like Listerine, take a second swab, and transfer it to the other side of the petri dish. Don’t forget to label which side is which! We swabbed one half of our agar plate with the mouth antiseptic first. Then, took two swabs – one for the non-antiseptic side of the plate and a second swab for the antiseptic side of the plate.
- •Discuss dependent variables, independent variables, and control variables with your students. It will be important to keep all of the petri dishes in the same area where they receive the same temperature and light. For example, you don’t want some of the dishes in front of a sunny window and others sitting behind a nearby curtain. You want to keep all of the Petri dishes in the same area where the temperature is the same.
- •If you’re testing dirty hands vs. hands that were washed with soap before swabbing, your independent variable is whether soap is used or not. If you opt to swab inside your mouth, then if you compare swabbing before using a mouth antiseptic, like Listerine®, using antiseptic vs. not is the independent variable. What independent variables will you test?
- •The dependent variable is the bacterial growth observed in the agar petri dishes.
Procedure for Growing Bacteria in Agar
Growing Bacteria in Agar
Equipment
- 1 Agar testing kit
Materials
- 1 kit Agar testing kit
- 1 piece permanent marker
- 1 copy lesson printout
- 1 pair safety glasses
- 1 pair disposable gloves
Instructions
- Determine where you will place the petri dishes while you wait for the colonies to grow. Try to place in a warm area between 78 degrees Fahrenheit and 100 degrees Fahrenheit. A warm room or incubator works well.
- Identify what you want to sample.
- Fill out the lab worksheets to label what is being tested.
- Wash hands, put on gloves, and put on eye protection.
- You will use one swab per surface swabbed.
- Run the swab over the first item or area you want to swab. Twirl the swab as you wipe to get material all over the cotton tip.
- Remove the lid from one agar plate.
- Gently roll the swab over the agar material. Do not press down too hard. Just run the swab over the agar.
- Place the cover back onto the agar plate.
- Dispose of the swab.
- Flip the agar dish over and write down the date, time, and what was swabbed. KEEP THE PETRI DISHES COVERED AND UPSIDE DOWN. Condensation may form on the inside tops of the dishes, and we do not want the condensation dripping down on the agar.
- Fill out the activity worksheets in the lesson printable.
- Place the petri dishes in a warm place. All of the dishes should receive the same temperature and light. The ideal temperature is between 78- and 100-degrees Fahrenheit. Do not open the dishes!
- Observe the petri dishes for 3 to 5 days and record your results.
- Once the activity is complete, wear gloves and eye protection and dispose of the dishes properly. Do not open the lids. Toss all gloves and disinfect the area where the dishes were sitting.
Photo Results – Growing Bacteria in Agar
What did you learn from growing bacteria in agar? What was surprising? What swab grew the most bacteria?
In our set of swabs, the cell phone swab was the clear winner for the biggest colony of bacteria. We thought the steering wheel would have more bacteria. We tested soap vs. no soap on hands and disinfectant vs. no disinfectant too. As expected, the swabs with soap and disinfectant had fewer bacteria than the non-soap and non-disinfectant swabs.
Complete the results and observations sections in the printable.
Get the Growing Bacteria in Agar Microbiology Lesson Printable & Extra High School Reading
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High School Level Extra Information
We have put together a 5 page read for high school and above. This reading lesson contains more information about bacteria, disinfectants, and antibiotics. We will soon add this information as a blog post.
I hold a master’s degree in child development and early education and am working on a post-baccalaureate in biology. I spent 15 years working for a biotechnology company developing IT systems in DNA testing laboratories across the US. I taught K4 in a private school, homeschooled my children, and have taught on the mission field in southern Asia. For 4 years, I served on our state’s FIRST Lego League tournament Board and served as the Judging Director. I own thehomeschoolscientist and also write a regular science column for Homeschooling Today Magazine. You’ll also find my writings on the CTCMath blog. Through this site, I have authored over 50 math and science resources.