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Germ Invasion

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Microbes are everywhere in our environment, but for the most part they escape our notice. This project shows you how to safely culture and study common bacteria from your everyday surroundings.


Areas of Science
Time Required
Average (6-10 days)
Material Availability
A kit for this project is available from our partner Home Science Tools.
Average ($40 - $80)
Follow the safety precautions for handling microorganisms listed in the Procedure.

Laurie Usinger, Bio-Rad Laboratories
Images courtesy of Bio-Rad Laboratories

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In this science project you will determine the microbial diversity present in your own everyday environment. Of the 100 million or so bacteria that are proposed to exist, how many distinct species can you identify? How can these different species be identified: By size, shape color, growth rate?


Microorganisms are the most fundamental, diverse, and prevalent biological organisms that inhabit the earth today. Prokaryotic microorganisms, organisms without a nucleus, can be generally divided into three classes: bacteria, protozoa, and fungi. By far the most predominant of these three classes of organisms are bacteria, single celled organisms which inhabit every type of environment on earth, and which have been in existence for greater than 3.5 billion years. Bacteria are ubiquitous, and are found in almost any environment. They thrive in the hot environments of deep sea sulfur vents, the frozen tundra of the Antarctic, the saline environments of the Dead Sea, and even extremely acidic environments such as the stomachs of organisms. In this science fair project, you will investigate what kind of bacteria, and how much bacteria, grows in different locations around your home.

Bacteria can be both pathogenic, responsible for a variety of diseases, and non-pathogenic, or harmless. Pathogenic bacteria are responsible for outbreaks of diseases like cholera, tuberculosis, and food poisoning. In contrast, non-pathogenic bacteria have many roles, including helpful ones! Some non-pathogenic bacteria lives in the stomachs and intestines of humans helping to break down foods and produce necessary nutrients such as Vitamin K. Moreover, a variety of naturally occurring antibiotics are synthesized from bacteria, such as streptomycin.

What kind of bacteria do you think live around your home? Try this science project to find out!

Terms and Concepts

Any basic biology text will have a chapter on prokaryotic organisms. Begin by reading a text on basic microbiology, such as Chapter 16 in Biology, Exploring Life, by Campbell, Williamson, and Heyden. Topics and terms which should be researched include:


Visit these websites for an introduction to bacteria:

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Experimental Procedure

Working with Biological Agents

For health and safety reasons, science fairs regulate what kinds of biological materials can be used in science fair projects. You should check with your science fair's Scientific Review Committee before starting this experiment to make sure your science fair project complies with all local rules. Many science fairs follow Regeneron International Science and Engineering Fair (ISEF) regulations. For more information, visit these Science Buddies pages: Project Involving Potentially Hazardous Biological Agents and Scientific Review Committee. You can also visit the webpage ISEF Rules & Guidelines directly.

  1. Identify 7 different locations where you would like to assess microbial biodiversity. Suggested sites could include the bathroom, kitchen, locations near heating vents, bedrooms, the refrigerator, the backyard, the garage, etc.
  2. At each site, place 3 nutrient agar plates. Use the permanent marker to label the bottom of each plate with its location. Leave the plates open and exposed for 3 hours.
  3. An additional 3 plates should be unopened and used as negative controls. In other words, you will study what grows on these plates even though you never expose them to the air. Hopefully, very little if anything will grow! Use the permanent marker to write "negative control" on the bottom of each of these plates.
  4. At the end of 3 hours, collect all the plates. Seal each plate with heavy-duty tape or saran wrap.
  5. Allow the plates to incubate by placing all of them in one single location that has a fairly constant room temperature (about 22 degrees Celsius) for 7-10 days, until distinct bacterial colonies can be observed. (Don't forget to put the 3, unopened control plates in this same location.)
  6. Collect data over the course of the experiment. Every other day, write down the number of colonies, the color, and the size in your lab notebook.
  7. After the end of the three week period, make various graphs of the data. Suggestions include, but are not limited to:
    1. Colony count on each plate.
    2. Colony count at each location (take an average of the 3 plates).
    3. Different types of microorganisms, based upon:
      1. Size
      2. Color
      3. Shape
  8. Keep the microbial plates until your science project is completely done, and while you are writing up your display board or other assigned summary. You will want to make many observations.

Discussion Points to Consider When Writing up the Conclusions of your Science Project

  1. Which environmental areas resulted in the most microbial growth?
    1. What environmental features unique to those locations might lead to microbial growth?
      • Moisture content?
      • Air circulation?
      • Cleanliness?
  2. Based upon your background reading, can you identify any of the bacterial/microbial colonies based upon their morphological features? Tip: The Science Buddies guide to Interpreting Plates should be helpful.
    1. Color?
    2. Shape?
    3. Size?
  3. If you had access to reagents in a biology laboratory, how could you use more sophisticated methods to type, classify, and characterize the individual colonies?
  4. Based upon your background reading, what percentage of the microbial organisms that are present in your environment did you isolate and identify?

Bacterial Safety

Bacteria are all around us in our daily lives and the vast majority of them are not harmful. However, for maximum safety, all bacterial cultures should always be treated as potential hazards. This means that proper handling, cleanup, and disposal are necessary. Below are a few important safety reminders.

  • Keep your nose and mouth away from tubes, pipettes, or other tools that come in contact with bacterial cultures, in order to avoid ingesting or inhaling any bacteria.
  • Make sure to wash your hands thoroughly after handling bacteria.
  • Proper Disposal of Bacterial Cultures
    • Bacterial cultures, plates, and disposables that are used to manipulate the bacteria should be soaked in a 10% bleach solution (1 part bleach to 9 parts water) for 1–2 hours.
    • Use caution when handling the bleach, as it can ruin your clothes if spilled, and any disinfectant can be harmful if splashed in your eyes.
    • After bleach treatment is completed, these items can be placed in your normal household garbage.
  • Cleaning Your Work Area
    • At the end of your experiment, use a disinfectant, such as 70% ethanol, a 10% bleach solution, or a commercial antibacterial kitchen/bath cleaning solution, to thoroughly clean any surfaces you have used.
    • Be aware of the possible hazards of disinfectants and use them carefully.

Explore More!

Interested in the science behind viral outbreaks? Check out Coronavirus.

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Ask an Expert

Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

Global Connections

The United Nations Sustainable Development Goals (UNSDGs) are a blueprint to achieve a better and more sustainable future for all.
This project explores topics key to Good Health and Well-Being: Ensure healthy lives and promote well-being for all at all ages.


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Many people work in environments that have obvious potential dangers, like collapses in mines, chemicals in laboratories, or machinery in factories, but there can be hazards in almost any job, like repetitive stress injuries from constant computer use or from scanning groceries. Occupational health and safety specialists identify potential hazards in a job, and then figure out ways to reduce the risks of accidents or injuries to workers or to the public. They also investigate accidents when… Read more
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General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Science Buddies Staff. "Germ Invasion." Science Buddies, 3 June 2021, https://www.sciencebuddies.org/science-fair-projects/project-ideas/MicroBio_p007/microbiology/germ-invasion?from=Blog. Accessed 26 Feb. 2024.

APA Style

Science Buddies Staff. (2021, June 3). Germ Invasion. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/MicroBio_p007/microbiology/germ-invasion?from=Blog

Last edit date: 2021-06-03
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