• Decrease font size
  • Return font size to normal
  • Increase font size
U.S. Department of Health and Human Services


  • Print
  • Share
  • E-mail

Science and Our Food Supply - Middle School Guide: Module 1 - Understanding Bacteria

Science and Our Food SupplyTeacher's Guide for
Middle Level Science Classrooms

2007 Edition

Return to Table of Contents



Module 1 - Understanding Bacteria - introduces students to the exciting world of bacteria and food safety.

Hand holding a pencil in a green circle background The Big Picture - explains that food safety is everyone's responsibility.

Empty flask and half-filled test tube in a green circle as background Bacteria Everywhere - shows that bacteria are everywhere and can spread from one surface to the next, potentially contaminating things that come into contact with food.

Hand holding a pencil in a green circle background The 12 Most Unwanted Bacteria - introduces a research project for the most common bacteria that cause foodborne illness.



Video tape in a green circle background This section explains the specific science concepts presented in Module 1 of the video/DVD, including fascinating facts relative to the module. Read this section before watching the video module or conducting the activities and experiments.

magnified image of Campylobacter jejuni

Magnified image of 
Campylobacter jejuni

Food Safety and the Battle with Bacteria

The United States has one of the safest food supplies in world, but there's always room for improvement. The battle to prevent foodborne illness is waged every day because bacteria are everywhere. Food safety has to do with controlling bacteria. And since everyone eats, we all share the responsibility for keeping our food free from harmful bacteria.


Electron Microscope

An electron microscope uses electrons instead of visible light to produce magnified images. It can magnify bacteria a million times their normal size.


magnified image of bacteria multiplying

Bacteria multiplying

Where Bacteria Come from and How They Grow

Bacteria are found everywhere, and under the right conditions, they can multiply fast! Each bacterium contains all the genetic information needed to make copies of itself. Bacteria multiply through binary fission, a process in which the cell's DNA doubles, the cell splits, and two independent cells are formed. Under the right conditions, a single bacterium will double with each division - 2 become 4, 4 become 8, etc. A single cell can turn into millions of cells in a few hours and billions of cells within one day!

This rapid growth is not usually a problem with good bacteria; however, when it occurs with bad bacteria (a.k.a. pathogens), it is "bad" news. As pathogens multiply, some give off harmful toxins or become infectious. If pathogens get into our food and multiply, people can get sick.


1 million bacteria can fit inside 1 square inch.


image of Dr. X
Dr.X, a crusading food
scientist, listing the 12
Most Unwanted

The 12 Most UnWanted Bacteria


Campylobacter jejuni
Clostridium botulinum
Clostridium perfringens
Escherichia coli 0157:H7
Listeria monocytogenes
Salmonella Enteritidis
Salmonella Typhimurium
Staphylococcus aureus
Vibrio cholerae
Vibrio vulnificus
Yersinia enterocolitica
Food thermometer showing the danger zone temperature as above 40 degrees F and below 140 degrees F
Danger Zone


Required Conditions for Bacterial Growth

Time/Temperature - Under the right conditions, some bacteria can double their numbers within minutes and form toxins that cause illness within hours. To minimize bacterial growth in foods, it's important to keep food temperatures below 40° F (4° C) or above 140° F (60° C). The level in between this temperature range is known as the Danger Zone.

Nutrients - Bacteria need many of the same nutrients as humans in order to thrive (glucose, amino acids, and some vitamins and minerals). For example, bacteria grow rapidly in high-protein foods like meat, poultry, eggs, dairy, and seafood.

pH range showing the level at which bacteria thrive
pH level

pH - Microorganisms thrive in a pH range above 4.6. That's why acidic foods like vinegar and citrus juices are not favorable foods for pathogenic bacteria to grow; however, they may survive.

Moisture - Most bacteria thrive in moist environments; they don't grow on dry foods. That's why dry foods like cereals can safely sit out at room temperature.

Note: If dry foods like dry cereals or spices become contaminated from infected hands or equipment, bacteria can survive on the food and make people sick, but they can't grow or multiply until the food is consumed.


  • Bacteria can multiply quickly - in fact, one cell can double within 20 to 30 minutes.
  • It takes less than 10 E. coli bacteria to make you sick.
Cook, Chill, Clean, Combat, cross contamination and Dr. X
The 4Cs of Food


How the 4 Cs of Food Safety Control Bacteria

If bacteria can grow so rapidly under the right conditions, then how do we control them? It's simple:

Cooking - kills bacteria by breaking down their cell walls and destroying enzymes, which they need to survive.

Chilling - slows down the bacteria's metabolism, thus slowing their growth. Not only can bacteria grow to large numbers and make people sick, but they can also spread everywhere. That's where cleaning and combating cross-contamination comes in.

Cleaning - removes bacteria from hands and surfaces.

Combating Cross-Contamination (separating foods) - prevents bacteria from spreading from one item to another.


bacteria mutating
Bacteria Mutating

Emerging Pathogens

Not only can bacteria multiply fast, but they can also mutate (adapt and evolve), a process that results in changes to genetic code. These changes happen very slowly and can make the bacteria better able to survive. They can change harmless bacteria into harmful bacteria, which often possess a new genetic characteristic like antibiotic resistance.


DNA molecules
DNA Molecules

How Scientists Can Tell Good Bacteria from Harmful Bacteria

DNA (deoxyribonucleic acid) is the "genetic blueprint" for all living things. A DNA molecule looks like a double helix that's shaped like a long ladder twisted into a spiral. The ends are joined to form a continuous loop, like a rubber band.

DNA contains the information that gives living things their traits or characteristics. In people, it determines things like physical features, behaviors, and even whether we're right or left-handed. In bacteria, the DNA molecule encodes the information that enables bacteria to grow, reproduce, and cause illness.

Scientists use DNA "fingerprinting," to identify similar groups of bacteria. DNA is treated so that it exhibits its own special pattern. When there is an outbreak of foodborne illness, epidemiologists (scientists who track down the causes of diseases and find ways to control them) try to determine the source of bacteria in foods by examining the pathogen's DNA "fingerprint." Then they see if it matches up to "fingerprints" (patterns) from other samples.


Hand holding a pencil in a green circle background (large)


Time: One 45-minute class period


This activity introduces students to food safety. It includes information about the number of people affected each year, the 4 Cs of Food Safety, the Farm-to-Table Continuum, who's responsible for keeping our food safe, and the link between food safety and science. The topic is launched by letting the students relate food safety to the foods they like to eat, such as hamburgers, orange juice, and salad. At the end of the activity, Module 1 of the video is shown to set the stage for "Understanding Bacteria."


Food safety is everyone's responsibility - everyone involved in growing, processing, transporting, and handling our food along all the points in our complex food distribution system. This responsibility includes all of us as we purchase, prepare, and eat our food. Students need to understand that food safety is a very serious issue that affects the well being of every individual. Because everyone must eat, we're all at risk of becoming ill if food becomes contaminated.





Set up a hot plate and skillet to cook the hamburger as students enter the room. Have a glass of orange juice and a salad sitting on your desk.



As students walk in, be cooking a hamburger to entice their senses. Other options are to post a large picture of the food in a conspicuous place, use food models, or dress up as a waiter/waitress. You can wear an apron and have a pad and a pen readily available for taking your students' orders. As the students come in, let them comment on the food. Don't give them an explanation. Let the atmosphere stimulate their curiosity.

CAN I TAKE outline of a chef stirring a pot YOUR ORDER?

Walk up to one student and ask: Can I take your order, please? How do you like your hamburger? What would you like on your salad?

Take 2 or 3 more orders and write them down. Then ask students (if they haven't already asked you): What do you think the hamburger, orange juice, and salad have to do with science?

List their answers on the board, then ask: Which of the foods would you most like to eat? What do you want on it? Is there anything that might be on the hamburger, in the orange juice, or in the salad that you didn't order?

You may have to give them a few hints. Hopefully, someone will mention bacteria. Then say: Aha! You have your first clue to the connection between these foods and science!

Now ask: Have you or has anyone you know ever become ill from eating food? Encourage students to express, when? what? and where? How could you get sick from a hamburger, orange juice, or a salad? (You can get sick if harmful bacteria are present in the food.)


  1. Use the following exercise to emphasize how prevalent foodborne illness is and to help students realize the seriousness of this issue and how it relates to them.
    • Ask students: How many of you have been affected by foodborne illness? Write that number on the board.
    • Now compute what percentage of the class thinks they've had foodborne illness.
    • Using that percentage, ask them to estimate how many students in the entire school might have had foodborne illness.
      (Note: Tell the students that this is only an assumption, and not an actual survey. This information is simply to help the students relate to the statistics that you are about to give them.)
    • Present this information on the board:

      Foodborne Illness in the U.S. (1999 estimates)
      76 million illnesses
      325,000 hospitalizations.
      5,000 deaths

      Centers for Disease Control and Prevention

    • There are approximately 274 million people in America. If 76 million people become sick due to foodborne illness, ask the students to calculate the percent of the population affected. Discuss the students' reactions to this percentage and have them relate it to the percentage calculated for the class. Then reiterate the importance of studying food safety.
  2. Let the students form the following 3 teams - hamburger, orange juice, and salad. Then ask: How do you think the hamburger, orange juice, or salad got to you? Let them brainstorm for about 10 minutes and list their ideas. This provides the segue to the Farm-to- Table Continuum.
  3. Show students the Food Safety Farm-to-Table illustration. Let them cross-check their lists with the Farm-to-Table Continuum. They may include even more steps, and that's good!
  4. Now ask: Whose responsibility is it to keep this hamburger, orange juice, and salad safe from harmful bacteria? Hopefully, the students will come up with it's everyone's responsibility, including their own once the food is in their possession. Discuss the reasons we all play a role in protecting our food supply.

Video tape in a green circle background TIME TO TUNE IN . . .Module 1 - Understanding Bacteria

Introduce the video by explaining: There's a lot of science behind keeping our food safe. Throughout this unit, you'll become food scientists and conduct experiments and research projects. Let's begin by meeting Dr. X, a crusading food scientist who's dedicated his life to fighting harmful bacteria and foodborne illness, and Tracy, a student working on her science video project, who teams up with him on his mission. I challenge you to uncover the following food-safety science links as you watch the video:

  • What 4 weapons does Dr. X use to fight harmful bacteria?
  • What is the significance of the mysterious O157:H7?
  • What is Dr. X referring to when he talks about the "baddest of the bad"?
  • What does DNA have to do with bacteria? What does it tell us?

Tell the students: You'll be conducting experiments and doing further research on many of the things you'll see in the video, so pay close attention! Show video/DVD Module 1 - Understanding Bacteria (Time: 15 minutes).

Video tape in a green circle background INSTANT REPLAY Time to review and summarize.

  1. Dr. X talked about his 4 food safety weapons for fighting harmful bacteria; what are they? (Clean, Cook, Chill, and Combat Cross-Contamination)
  2. What's the significance of O157:H7? (E. coli O157:H7 is one kind of E. coli that causes foodborne illness. E. coli O157:H7 evolved from the harmless E. coli bacterium.)
  3. Dr. X described the "baddest of the bad"; what was he referring to? (The 12 Most Unwanted Bacteria that cause foodborne illness)
  4. What does DNA have to do with bacteria? (DNA encodes the information that enables bacteria to grow, reproduce, and cause illness.)
  5. What does DNA tell us? (When there is an outbreak of foodborne illness, epidemiologists use the pathogen's DNA fingerprint to determine the source of the bacteria.)
  6. What does science have to do with food safety? (Food safety has everything with controlling bacteria. There are all kinds of scientists dedicated to developing methods to keep our food supply safe.)
  7. Whose responsibility is it to keep our food supply safe along the Farm-to- Table Continuum? (It's everyone's responsibility.)
  8. What effect do each of the 4 Cs have on bacteria? (Cleaning removes bacteria from hands and surfaces. Cooking (heat) kills bacteria by breaking down their cell Chilling slows down the bacteria's metabolism, thus slowing their growth. Combating Cross-Contamination prevents the spread of bacteria from one thing to another.)


UP NEXT . . .
Bacteria are everywhere - even in this classroom! In the next activity, you'll join Dr. X's crusade by finding where these organisms live and thrive.


SciLinks Logo
Keyword: Food Safety
Go to: www.scilinks.org disclaimer icon
Code: FS300


It's everyone's responsibility to control the spread of bacteria - from the farmer, the food processor, the person who transports our food, people who work in supermarkets and restaurants, and consumers when they take the food home.


  • Check the Internet to learn more about when and why food safety became a National Initiative.
  • Collect articles on food safety from your local paper and TV news reports, and write a report on local food safety issues. Post articles and reports on the class bulletin board.
  • Check out the Food Safety A to Z Reference Guide, particularly the 4 Cs section.
  • Survey people in your class/grade/school/ faculty to find out how many of them may have experienced foodborne illness.

Career Connection icon with lab coat (large)

See real-life scientists in action!

  • Food Safety A to Z Reference Guide



Empty flask and half-filled test tube in a green circle as background (large)


Time: Two 45-minute class periods



Students will be challenged to hypothesize about where most bacteria are found. They will develop an awareness that bacteria are everywhere and that various surfaces might have different levels of organisms. Students will learn how to work safely with bacteria. In the extension activity, they'll hypothesize about how to control the spread of bacteria. The skills learned in this lab will prepare the students for other experiments and activities in the food-safety curriculum.


Bacteria can spread from hands to food, from food to food, and from surfaces to food. Cross-contamination can be controlled by thoroughly washing hands and surfaces.




For the Class

  • Dissecting microscope or hand lens to view microbial colonies
  • Additional sterile Petri dishes with nutrient agar and covers for expanded tests
  • Disinfecting solution to disinfect lab surfaces (20 ml of liquid household bleach in 1 L of tap water, see Laboratory Procedures)

For Each Team of 3 to 4 Students

  • 3 sterile Petri dishes with nutrient agar and covers
  • 2 cups of sterile water
  • Sterile cotton swabs
  • Parafilm or masking tape to seal the dishes
  • Permanent marker
  • Safety gloves
  • Lab Report Outline for each student
  • Bacteria Everywhere Data Table to record results


  • Prepare or order 3 sterile Petri dishes containing nutrient agar for each team of 3 to 4 students. You may want to order extra plates for students who want to test additional areas. Note: Petrifilm™ plates can be used instead of Petri dishes. See Resources.
  • Sterilize (boil) 2 cups of tap water for each team. You can boil the water in beakers and then cover with aluminum foil until ready to use. Students will use the water to wet swabs for testing dry surfaces.
  • Photocopy the Lab Report Outline for each student.
  • Photocopy the Bacteria Everywhere Data Table for each team.



As students walk into the classroom, be peering through a large magnifying glass in search of bacteria in various sections of the classroom. Your students will wonder what you're doing. Explain to them: Like Dr. X, I'm on a mission - to find out where bacteria live and how they thrive. Now tell them: You're going on a microorganism safari, and during this safari you're going to become "science sleuths." Your assignment is to find areas where bacteria are living and come up with a plan to determine which areas have the most and least bacteria.

Get the students started by asking:

  • Are there bacteria in this classroom? Where?
  • Where else might they be living around the school?

Make a list of the responses.

Some probable answers:

  • Soda machines, door knobs, desks, trash cans, door handles, water fountains, faucet handles, bathroom stall doors, toilet seats, biofilm in sink drains, handle on paper-towel dispenser, lab tables and counters. Allow the students to mention things at home, but tell them: For today, let's investigate bacteria here at school.
  • If they haven't mentioned their hands, under fingernails, etc., ask: What about you? Could bacteria be on you? Now ask: What do bacteria look like? (Let them discuss this.) Can you see them? If you can't see them, how can you tell that bacteria really exist? This leads us into today's lab. We're going to design experiments that allow us to "see" bacteria.


LAB 1 Find The Bacteria


This lesson involves the following 3 steps in gathering information:

  1. Isolate the sample.
  2. View the sealed plates under a dissecting microscope or a hand magnifier.
  3. Consider the number of organisms and the diversity of the colonies.
  1. Have students work in teams of 3 or 4. Ask each team to select a name and choose at least 4 or 6 areas to examine. Have the students try for as many different areas as possible, but make sure the important areas, such as hands and/or under the fingernails, are tested by at least 2 teams. (If students are searching for bacteria on their hands or under their fingernails, they should wash their hands after they swab those areas.)
  2. Now, have each team hypothesize about which areas will have the most bacteria. Which will have the least bacteria? Why? How fast will the bacteria grow? Why?
  3. Have them design an experiment to test their hypothesis.
  4. Let each team present their hypothesis and experimental design to the class. Encourage students to discuss the merits of each suggested test. This is also an important time for "guided inquiry. "For example, you can guide them by asking a question such as: How can you be sure that your agar isn't contaminated?
    (You should always have a control plate). After the group discussions, give teams time to revise their hypotheses and experimental designs.
  5. Show students how to swab a surface (on dry surfaces use a moist swab) and inoculate a Petri dish (see Laboratory Procedures). These procedures will be used throughout the unit.
  6. Review the important rules of lab safety, especially the handling of bacteria in Petri dishes.
  7.  Give each team 3 Petri dishes. Ask them: Is there anything you should do with these dishes before you start your experiment?
    • Label the dishes on the bottom (agar side).
    • Divide the control dish into thirds. Label the control plate: agar, wet swab, and dry swab. Then swab the control plate.
    • Divide and label the other 2 dishes with the areas they want to test.
    • Label the dishes with the date, their team name, class, and hour to avoid mix-ups. Label along the side, so you can see the bacterial growth in the center. For easy and fun identification, students can swab the plates using their initials.
  8. Give the students 10 to 15 minutes to gather their samples and inoculate their dishes.
    • Tape Petri dishes closed.
    • Place dishes in an incubator at 35° C (95° F) or let the dishes sit at room temperature for the appropriate amount of time.
    • Ask students to set up time parameters - the number of hours or days they think it will take for the bacteria to grow.



  • Wash hands thoroughly before and after the lab.
  • Disinfect all lab surfaces before and after working in the lab (see Laboratory Procedures).
  • Wear safety gloves.
  • Seal inoculated Petri dishes using Parafilm or masking tape (see Laboratory Procedures).
  • Remind students never to open a dish with organisms growing in it. Some organisms could be dangerous pathogens.
  • After the experiment is completed, discard all disposable dishes using safe techniques (see Laboratory Procedures).

LAB 2 Observe Bacteria and Record Results


  1. This lesson involves the following 3 steps in gathering information:

    1. Isolate the sample.
    2. View the sealed plates under a dissecting microscope or a hand magnifier.
    3. Consider the number of organisms and the diversity of the colonies.
    Have students observe the bacterial growth and record the results. Students can use the Bacteria Everywhere Data Table to record their results. Tip: Ask the students to draw their Petri dishes on the back of the Data Table and illustrate the organisms that are growing.
  2. Students can analyze the results based on their observations. Ask them:
    • What do you see? (Their first observation may be the number of bacterial colonies. If so, use a 0-5 scale for rating the quantity. Guide students in ranking the results.)
    • What else do you notice about the colonies? (Their next observation may be the size and shape of the organisms.)
    • Why do they look different? (Different microorganisms have different characteristics.)
  3. Have each team report the following to the class: the areas they sampled, the number of organisms they observed, and the characteristics (size, shape, and color) of the organisms.
  4. Ask students: Were there any differences in your results compared to the other teams? How did your results support or reject your hypothesis?
  5. Are the organisms good or harmful organisms? (With this experiment, students will not be able to identify good versus harmful organisms - they would need specific agars to grow and identify specific organisms. The purpose of the experiment is to demonstrate that bacteria are everywhere and different surfaces have different levels of organisms. Also, stress that not all bacteria are harmful. In fact, most bacteria are beneficial to us.)
  6. Be sure to properly dispose of the Petri dishes.
  7. Ask students to write a lab report (see the Lab Report Outline).

INSTANT REPLAY  Time to review and summarize.

Video tape in a green circle background (shown in The Big Picture activity)

  1. How do bacteria multiply?(Bacteria multiply through a process called binary fission - where the cell's DNA doubles. The cell splits and two independent cells are formed.)
  2. How fast can bacteria multiply? (Bacteria can multiply really fast - from a single cell to millions in 10 to 12 hours!)
  3. What's the difference between an electron microscope and a light microscope? (Electron microscopes magnify way beyond what our light microscopes do. They magnify images up to a million times their actual size, and they use electrons instead of visible light to get magnified images.)
  4. In the video, why was Dr. X so concerned about what happened at the Barkley house? (The cutting board that Mr. Barkley used to prepare the raw poultry was not properly cleaned before Alex used it to cut up raw vegetables for the salad. Dr. X was concerned that the raw juices from the poultry could have contaminated the raw vegetables.)

Empty flask and half-filled test tube in a green circle as background Lab Procedure:

  1. How do you know the agar and swabs used to collect samples were free from microorganisms? (Make a control plate.) If the agar or swabs were not free from microorganisms, explain how this would affect your results. (Results could be misleading because of contamination.)
  2. What do the data you've collected have to do with the food you eat? (Bacteria are everywhere and can be transferred from surfaces to food and from hands to food.)
  3. Why do certain surfaces have more bacterial growth than others? (Bacteria thrive in certain environments depending on the moisture level, temperature, time, pH, etc.)
  4. How would you know if the organisms you observed were harmful or not? (You would need specific agars to grow and identify specific organisms, so in this experiment you wouldn't know.)
  5. Are all bacteria bad? (No, most bacteria are beneficial to us.)

Application to Food Safety:

  1. How can bacteria transfer from objects to foods, from people to foods, and from foods to other foods? (By contact with contaminated objects, hands, and food)
  2. Which of the 4 Cs applies to the data you've collected? (Clean and Cross- Contamination)
  3. Why is it important to thoroughly clean some surfaces more than others? (Bacteria thrive in some areas more than others because some areas may have more opportunities for contamination and for growth.)
  4. What are your suggestions for cleaning surfaces during food preparation? (Allow student suggestions.)
  5.  Based on your findings, what advice would you give to people who prepare food (restaurant workers, cafeteria workers, etc.) to help prevent the spread of harmful bacteria? (Clean surfaces thoroughly, properly wash hands, and don't cross contaminate surfaces and foods.)


SciLinks Logo
Keyword: Bacteria
Go to: www.scilinks.org disclaimer icon
Code: FS100


Bacteria are everywhere and can spread from surface to surface, person to person, food to food, and person to food. Harmful bacteria can be controlled by practicing the 4 Cs of Food Safety. To prevent the spread of harmful bacteria, proper cleaning of both hands and surfaces is especially important. The good thing is that not all bacteria are harmful; most bacteria are beneficial to us. When designing experiments, you should always use safe techniques when working with bacteria. Also, it's important to have a control plate.


  • Research the following questions:
    - Is it possible to eradicate all bacteria from the environment? Why or why not?
    - Would this be a good idea? Why or why not?
    - What essential functions do bacteria play in the environment?
  • Also try the following:
    Bacterial Reduction Activity
    1. . Write a hypothesis and design an experiment to remove or reduce the amount of bacteria on the areas where you saw bacterial growth. Test variables such as:
      • Different techniques, e.g., rinsing hands with water versus washing with soap and water, versus not washing at all.
      • Washing hands for different times: 10 seconds, 15 seconds, 20 seconds.
      • Other variables that you might suggest.
    2. Record your predictions on your Lab Report Outline.
    3. Design the experiment with your team, consult with your teacher for guidance, and carry out the test.
    4. Conduct the experiment using a more quantitative approach:
      • Swab the surface.
      • Transfer the swab to 10 ml of buffered saline and mix.
      • Inoculate Petri dishes from the liquid.


Career Connection icon with lab coat (large)

See real-life scientists in action!

  • Food Safety A to Z Reference Guide


UP NEXT . . . The worst. The baddest of the bad! The 12 Most Unwanted Bacteria. Discover what foodborne illnesses they cause and how to control them.



Name __________________________________________________ Date ___________ Class/Hour _____________

(Write in complete sentences. Measure in metric.)

1. Problem
(What question are you investigating?)
2. Hypothesis
(What do you think will happen?)
3. Materials
(List the supplies needed to conduct the experiment.)
4. Procedure
(List the steps followed to complete the experiment.)
5. Data/Organization/ Interpretation
(What did you see, hear, or smell? You should use a graph, chart, and/or illustration.)
6. Summary
(Explain the results using science vocabulary.)
7. Further Questions
(Good scientists always think of something else they'd like to try!)


Name __________________________________________________ Date ___________ Class/Hour _____________

LAB 1 - Find the Bacteria
Choose the Areas to Be Examined Hypothesize the Least/Most Abundant Areas
LAB 2 — Observe and Record the Results
Rank the Amount of Microorganisms - 5 (most) 0 (least) Describe the Size, Shape, and Colors of Organisms


Hand holding a pencil in a green circle background (large)


Time: One 45-minute class period to set up the activity
One 45-minute class period for team presentations


Students will divide into teams and select a bacterium from The 12 Most Unwanted Bacteria reproducible to research throughout the food safety unit. Each team will relate all subsequent activities and experiments in the unit to their bacterium and conduct an innovative presentation at the end of the unit. Each team will be able to recognize the foodborne illness that their bacterium causes and understand how to control that bacterium.


Foodborne bacteria can have a major impact on public health. Everyone is susceptible to foodborne illness, especially the "at-risk" populations, including young children, pregnant women, the elderly, and people with weakened immune systems. There are four simple steps to preventing foodborne illness: clean, cook, chill, and combat cross-contamination.




  • Write the name of each bacterium from The 12 Most Unwanted Bacteria reproducible on separate pieces of paper and place them in a bowl. Teams of students will randomly select a bacterium to study throughout the unit.
  • Photocopy background material on each of the 12 Most Unwanted Bacteria from the Food Safety A to Z Reference Guide.
  • Photocopy The 12 Most Unwanted Bacteria reproducible for each student.
  • Collect actual foods, pictures, or models of foods that contain good bacteria (e.g., cheese, yogurt, etc.)
  • Set a due date for the final team presentations.


For the Class

  • A bowl containing the names of the 12 Most Unwanted Bacteria
  • Foods, pictures, or models of foods that contain good bacteria, such as cheese and yogurt

For Each Team of Students

  • A food safety portfolio for recording research data (use a notebook or folder)
  • An assortment of items for final presentations
  • Photocopy of background information for their chosen bacterium
  • Photocopy of The 12 Most Unwanted Bacteria reproducible for each student



Ask students: What do you usually see on a "Most Wanted" list? Hopefully, students will respond with "bad guys" or "criminals." Then hold up a copy of The 12 Most Unwanted Bacteria reproducible and ask: Does anyone know why these are "unwanted"? (They're pathogens that can be found in foods and can make us sick if we eat them.) Distribute the reproducible. Continue the discussion with:

  •  Are any of these familiar to you? Which ones? What have you heard about them?
  •  Are all bacteria bad? (No, most bacteria are beneficial to us in our everyday lives.)
  • If I asked you to make a poster of "Wanted Bacteria," what would you put on that poster?
  •  Have you ever eaten foods that contain bacteria?
  • Have you ever eaten this? (Show a picture or a slice of cheese, and/or a container or picture of yogurt.) What do these foods have in common? (They all contain beneficial bacteria.) Can you think of some other foods that contain good bacteria? (Some examples: buttermilk, sauerkraut, pickles - even wine and beer.)
  •  Are you surprised that these foods contain bacteria? Why?
  • Where else might we find good bacteria? (Examples could include: In our small intestine there's generic E. coli, which helps us digest our food; and in antibiotics like Streptomycin, which helps treat patients with infections.) Explain to the class: In this activity we're going to focus on some harmful bacteria that can make us sick and explore why Dr. X considers these bacteria the worst, "the baddest of the bad!"


  1. Divide students into 12 teams. Have a person from each team select a pathogen from the bowl.
  2. Ask the students what they'd like to know about bacteria in order to become "super science sleuths." Write their answers on the board.
  3. Give a food safety portfolio to each team. Challenge them to be constantly on the lookout for information about their pathogen and to record their findings in their portfolio. Remind them to include the date, URL for Web sites, title, author, year, and page numbers of books or articles.
  4. Have each team divide the questions on The 12 Most Unwanted Bacteria reproducible equally among members of their team, so that everyone in the group has a task. The reproducible can be used as a checklist during their research.
  5. Give each team background material on their selected pathogen from the Food Safety A to Z Reference Guide to get them started.
  6. Explain that each group will work together to:
    • Conduct in-depth research about their pathogen.
    • Find out how their pathogen makes an impact on food safety along the Farm-to-Table Continuum.
    • Discover what can be done to control the growth of their pathogen.
    • Present their research to the class to teach other students about their pathogen. Give students a date for their presentations.

Planning the Final Presentation

  1. Explain to the class that at the end of the food safety unit, each team will present their research to the class in a fun, creative way. The presentation should be a maximum of 5 minutes. Students can use the following suggestions or come up with their own ideas.
  2. Since one of the purposes of the presentation is to share what they learned about their bacterium with the other students, each team should prepare a simple fact sheet on their bacterium for the other teams to add to their portfolios. At the end of the presentations, each team will have information on all the 12 Most Unwanted Bacteria.

Ideas for Final Presentations


  • Perform a skit using your pathogen as the main character.
  • Dress up as your pathogen and perform a moving monologue.
  • Create a poem, song, dance, or rap about your mighty microbe.
  • Produce "Jeopardy" or "Who Wants to Be a Millionaire?" type game shows.
  • Put on a news broadcast about a real outbreak involving your pathogen.
  • Put on a puppet show or create picture books to share with primary school students.


  • Prepare posters or 3-D models of your pathogen to hang around the classroom, using assorted materials (coat hangers, newspapers, papier mâché, balloons, cardboard, plastic bottles, poster board, fabric scraps, pipe cleaners, and beads).
  • Design a food safety calendar with a theme for removing or eliminating your pathogen for each month of the year.
  • Design and prepare Web pages that offer photos and facts about your pathogen.
  • Develop an animated slide show, using Power Point slides and clay animation.
  • Design a travel brochure with graphics and text tracing the journey of your pathogen.
  • Create an animated flip book about your microbe.


  • Interview your pathogen like Dr. X did in the video.
  • Write humorous comic strips featuring your pathogen.
  • Create a recipe book filled with food safety tips for avoiding your pathogen.
  • Write a moving story about a day in the life of your pathogen.

Create Video

  • Create a video pertaining to your pathogen using one of the following styles - documentary, newscast, drama, advertisement, or game show.


  • After completing each activity and experiment in this food safety unit, remind the teams to add what they've learned about their bacterium to their food safety portfolio. Encourage them to also include information they've discovered from their own research.
  • Throughout the unit, periodically check the students' food safety portfolios to evaluate their progress and give guidance on additional research.



SciLinks Logo
Keyword: Foodborne Illnesses
Go to: www.scilinks.org disclaimer icon
Code: FS301


A pathogen is any microorganism that is infectious and causes disease. There are bad bacteria (pathogens), such as the 12 Most Unwanted Bacteria, that cause foodborne illness. However, not all bacteria are bad. Good bacteria, such as those found in foods like yogurt and pickles, and those in antibiotics like Streptomycin, are helpful to us.


  • Be on the lookout for reports about your pathogen in local newspapers, on TV news reports, and on the Internet. These newsworthy reports can be added to your food safety portfolios.
  • Take a virtual field trip to the American Museum of Natural History's "Epidemic! The World of Infectious Disease".
Career Connection icon with lab coat (large)

See real-life scientists in action!

  • Food Safety A to Z Reference Guide


UP NEXT . . . Put on your boots! We're going to the farm with Dr. X to meet his scientist friends who will introduce us to the first step in the Farm-to-Table Continuum.