Grow Germs Using Nutrient Agar
In this science experiment, kids use nutrient agar to grow germ specimens.
SAFETY NOTE: ADULT SUPERVISION REQUIRED. Germs can be dangerous and should not be touched or allowed to become airborne. Once this experiment is started, it must remain sealed and be properly disposed of. Preparing the agar also involves very hot water.
Germs, also called microbes, are so small that you need a microscope to see them. But rest assured – even if you can’t see them, they are everywhere! In fact, your body and most other things are covered with germs. Most are bad for you, but some are good!
Bacteria and viruses are both examples of germs.
Bacteria are single-celled organisms that live just about everywhere on Earth – from boiling hot volcanoes to freezing cold icebergs. They can survive in environments where we humans cannot, and survive by eating everything from sugar to sunlight. Bacteria are very tiny; for example, 10 million can be found on your desk at school! They can cause sicknesses like tonsillitis, strep throat and ear infections.
Most viruses are a thousand times smaller than bacteria. Unlike bacteria, viruses don’t have their own cell; they need to borrow a host cell, like a blood cell, to survive. Viruses come in many funny shapes – some look like round popcorn balls while others have more complex shapes that look like spiders. Viruses can spread quickly and cause sicknesses like chickenpox, the flu and the common cold.
Germs are a fact of life; they are everywhere, all the time. Though it’s important to avoid harmful germs by keeping your hands and body clean, there really is no way ever to get rid of the germs all around you. That’s why your body has a highly effective system for dealing with germs – called your “immune system.” It acts like a superhero would, defending your body against invading germs. For example, the tears in your eyes wash away and kill the germs that try to enter through your eyes; mucus traps germs and keeps them from entering your body through your nose; saliva kills the bacteria that try to enter through your mouth; the acids in your stomach kill the germs that manage to get past your saliva; and your white blood cells help attack and remove any harmful germs that start to float around your body.
It is important for us to study germs because they affect our bodies in many ways. Though many germs are harmful and cause us to get sick, scientists are learning that some germs are actually good for us! For example, some germs in our mouths prevent other harmful germs from growing there; some are used in vaccines to keep us healthy; and some help us digest our food.
In fact, if you've ever eaten yogurt, you've eaten healthy bacteria! Two types of bacteria are used in making yogurt: Lactobacillus Bulgaricus and Streptococcus Thermophilus. During the yogurt-making process, bacteria are added to milk; this causes a specific kind of fermentation to occur, which converts the milk into yogurt. These bacteria remain alive even after the yogurt is packaged and sent to the store. A similar process is used to make other dairy products, such as sour cream. Not only is this type of bacteria safe to eat, scientists believe these live bacteria may actually be good for your health by helping your digestive system, boosting your immune system and even fighting certain types of cancer.
Ever wonder how you can protect yourself from germs? Wash your hands! Soap and water work best in the fight against germs.
Nutrient agar is made up of ingredients that will support the optimal growth of germs. It includes elements that the germs can both grow on and feed on.
- Prepared Nutrient Agar - 1 of this item per student
- Petri dishes - 1 of this item per student
- Sticker labels
- Cotton swabs
- Invisible tape
- Stovetop or Microwave
If you are working in a classroom and will be sending these experiments home, please make labels to put on the Petri dishes to indicate that the kids (1) should never open the experiment, and (2) should throw it away unopened in 2 weeks. Better yet, just keep the Petri dishes in the classroom for the kids to observe there.
ADULT SUPERVISION REQUIRED. Prepare the nutrient agar according to the package directions. The agar will be hot, so you likely will want to put it in the refrigerator for a few minutes to cool. MAKE SURE IT DOES NOT COMPLETELY GEL IN THE REFRIGERATOR.
For best scientific results, sterilize the Petri dishes by boiling them.
Pour the liquid agar into the Petri dishes. Replace the lid and return to the refrigerator until solid -- about 30 minutes.
Once the agar is solid, remove the Petri dishes from the refrigerator.
Using a cotton swab, dab a germy spot -- such as your hands, the phone or a remote control -- to collect a germ sample.
Remove the petri dish lid. Swab the same cotton tip onto the solid agar to transfer your germ sample and replace the lid.
Repeat until you’ve used all of your Petri dishes. Be sure to label them so you’ll know which germs came from which location.
Tape the dishes shut completely. As an extra precaution, you may also want to put the taped Petri dishes inside a sealed zipper bag.
Never open the sealed Petri dishes; simply watch the germs grow through the lid. If any germs were transferred to the agar, they should begin to grow within a few days.
Use a magnifying glass to examine the germs, and compare them to images you find online to see if you can identify the type.
In 2 weeks, throw your Petri dishes away. Do not open them!
If you don't have Petri dishes, try pouring the agar into foil cupcake liners placed inside muffin tins, or inside sterilized recycled jar lids. Just be sure to seal these well with plastic wrap or similar.