Study Household Microbes
(Bacteria and Fungi)

You may grow household microbes such as bacteria and fungi for different reasons. For example you may want to view them under microscopes or see the shape of their colonies or see how different antiseptics or germicides may affect them.

There are about 13 different science projects or science experiments listed at FreeScienceProject.com that require growing bacteria.

See all 13 projects

In order to study bacteria, you need to grow bacteria. Bacteria can grow in flasks with proper nutrients, but if you want to count bacteria or observe the shape and color of bacteria colonies you will need to grow bacteria in petri-dishes.  Bacteria growth Science set contain the supplies that you need in order to conduct many different bacteria growth experiments. The same material and supplies can be used for many other chemistry and biology projects as well.

In a bacteria growth science set you will find the following items:

1. 20 sterile clear plastic petri-dishes
2. 5 sterile and individually wrapped 5ml pipettes
3. 5 sterile and individually wrapped 1ml pipettes
4. 5 clear plastic test tubes with screw caps
5. 5 sterile and individually wrapped transfer pipettes
6. Fine U.S.P. grade agar (about 7grams in one clear test tube or about 15 grams in one glass bottle)

You can use the material in this kit to experiments on collecting and growing household bacteria. When you grow bacteria, you will then be able to go further and research on bacteria and factors affecting their growth and reproduction.

Bacteria are single-celled micro organisms that play an important role in many ecosystems. Bacteria vary in terms of morphology, oxygen and nutritional requirements and motility. Bacteria may be free-living, live on dead or decaying organic matter (saprophytic), or pathogenic in plants or animals. Bacteria reproduce by fission. 

In order to grow bacteria, you will need culture media, plates or petri-dishes and some laboratory supplies and an incubator. 

Culture Media: Culture media is a moist or liquid matter that contains nutrients for bacteria. Almost any nutrient food may be considered a culture media for general bacteria, however if you want to grow a specific bacteria or prevent growing some other bacteria, you will need to use a fine tuned recipe for your culture media. 

Chicken broth and beef broth are among nutrients that most bacteria can use. In some recipes you may also add some mushroom extract. Sugar can also be added to some culture media. Small amounts of some minerals such as potassium phosphate and calcium carbonate may also be added to the culture media. Note that there are many foods that are good for growing bacteria, but they are not good as culture media. For example bacteria can easily grow on milk, but milk is not a good culture media because it will change by the activity of bacteria. Part of milk solidify when bacteria produce acids. A good culture media must be clear and must remain liquid and should not easily change pH. If you need to solidify your culture media, use agar to do that. Agar is a gelatinous substance that is extracted from sea weeds. If we need to grow bacteria for the purpose of identification or counting, we need to grow bacteria in nutrient agar plates. These are petri-dishes containing a mixture of agar and nutrients.

See More Details about making Nutrient Agar Plates at home

Incubator: Incubator is a warm cabinet that you can set its temperature to a proper temperature for bacteria growth. About 35º C is a good temperature for most bacteria. This is close to the body temperature. If you are able to create such a temperature in any other way, it is as good as an incubator. You may find warm places behind your refrigerator, next to the radiator or inside an oven that is off.

You may also make an incubator by placing a small desk lamp inside a wooden or metal box. Or you may put a Styrofoam cooler upside down over a desk lamp. A small lamp (15 watts) should be able to create enough heat to warm up a small space. Prepare your incubator in advance and use a thermometer to test it a day before starting your experiment.

* Chicken broth or beef broth can be purchased from supermarkets and health food stores or you may make them at home. (It must be fat free). Filter paper is coffee filter or you may substitute it with any clean cotton cloth. 

How to prepare nutrient agar plates?

Prepare the nutrients such as chicken broth or beef broth and boil it with some mushroom. Let it cool off to the room temperature and filter it to be clear. Add  water to bring it to 800ml to 1000 ml. Add 7 to 10 grams of agar and stir it to make an emulsion.

• If you have purchased a kit with a test tube of agar powder, it contains about 7 grams of agar. Use all of that for 800 mL up to 100 mL nutrients. 
• If the agar comes in a glass bottle, it is 16 grams. Use half of that for 800 mL nutrients.  

Reheat the emotion while stirring until it boils for about one minute. Your nutrient agar is now ready. Let it cool to about 45ºC. At this time you can pour the nutrient agar solution in petri-dishes and place the lid. The amount of nutrient agar in each plate must be enough to cover the bottom of the plate. Agar will solidify in plates. 

Note that boiling does not kill all the bacteria and your agar and your plates may not be sterile at this time. If you have access to an autoclave, place your plates in autoclave for about one hour at the temperature of 135ºC. Without autoclave your results will not be reliable and some unexpected bacteria may grow in your nutrient agar.

You can keep your nutrient agar plates in a refrigerator for later use. When you are ready to use a plate, remove it from the refrigerator and keep it in room temperature for a few hours. 

To grow bacteria, use a pipette to drop 0.1 ml of infected water or any other sample on one agar plate and spread it on the surface of the agar using an sterile glass rod or spoon. Place the plate in an incubator or any other place with a temperature of about 35ºC. Within 24 to 48 hours you should be able to observe bacteria colonies.