Safe Food For the Hungry -- II
Learning Center Activities Part 1: Food Safety
Learning Center Activity 2: The Microbial Zoo Lesson Plans
During this activity participants will:
- learn that microorganisms are everywhere
- learn the importance of good sanitation
- bacterial sources for inoculating plates
- petri plates containing sterile nutrient agar
- sterile cotton swabs
- masking tape and scotch tape
- marking pens
Preparations for activity:
- Obtain petri plates with sterile agar. You may be able to get these from a science
teacher, university, or hospital.
- Collect the bacterial sources you wish to use to inoculate the plates. Suggestions
- dirty fingers
- clean fingers
- gloved fingers
- gloved fingers after touching face/hair/etc.
- coin (not a penny)
- raw meat
- drag finger across a table, floor, counter.
- Inoculate the petri plates using a different bacterial source for each plate.
- fingers - gently touch fingers to the agar. lips - touch your lips lightly to the
agar (kiss the agar). Note: agar is nontoxic.
- hair - remove a piece of hair from your head and gently lay it on the agar. Try
to avoid touching the agar with your fingers.
- cough - hold the plate 2-3 inches from your mouth and cough directly onto the agar.
- coin - place a coin (not a penny, the copper will keep many microorganisms from
growing) on top of the agar in the middle of the plate. Or, gently rub or roll the
coin over the surface of the agar (try not to dig a hole in the agar).
- saliva - place a clean cotton swab in your mouth and moisten it with saliva. Gently
rub the moistened swab over the surface of the agar.
- raw meat - place a small piece of raw meat (i.e. ground beef) on top of the agar
in the center of a plate; or gently rub the meat over the surface of the agar.
- nose - place a clean cotton swab in your nose and move it around with a circular
motion. Gently rub the moistened swab over the surface of the agar.
drag finger across the floor or a counter top, then trace an S pattern on the agar
with the same finger.
Instructions for activity:
- Label the bottom of each plate with the a code (a, b, c, ...). Make a key with the
code, date of innoculation, and source of bacteria for each petri plate.
- Tape each plate closed by running scotch tape around the edge of the plate.
- Place the plates upside down in a warm place (70-85 oF)
to grow. Note: Keep the plates away from windows since UV light kills bacteria.
You incubate them upside down so that the moisture droplets that form don't fall
on the agar. When plates have grown the desired amount (3-4 days) place them in
the refrigerator until you are ready to use them.
- Hang sanitation posters and the bacterial "Most Wanted" posters on the wall.
- Place coded petri plates on a table in front of the posters.
- Post the Microbial Zoo fact sheets and Instruction Sheets.
- Post the petri plate key.
- Take used petri plates to an appropriate place for disposal, for example, a high
school science teacher, a hospital, or a university.
Learning Center Activity 2: The Microbial Zoo Background Information
Bacterial Plating Experiment - Discussion Sheet
The nutrient agar in the petri plates is a general purpose food source for microorganisms.
Although not all microorganisms like it, many do and will grow.
Use the information on this page when examining the petri plate display. Note the
- # colonies seen
- color of colonies
- presence of fuzziness
- shape of colony (blob)
- any other characteristic observed
It is not important to identify the organisms on the plates. These plates illustrate
the fact that microorganisms are everywhere and can grow under favorable conditions.
Don't open the petri plates!!
- Fuzzy things are molds. You will frequently see molds that are green, black, or
white. Some molds are good, like the Penicillium mold that provides us with the
antibiotic, penicillin. Some molds produce toxins that can make us very sick. Some
molds make our food look, taste, or smell bad.
- Blobs that aren't fuzzy may be bacteria or yeasts. Some yeasts are used to make
foods, like the yeast that makes bread rise or the yeast that turns the sugar in
grapes to alcohol in wine.
- Each blob is a colony. Each colony is made up of millions of individual cells. Each
colony started out as a single cell (one microorganism).
- Note the different colors and shapes of the colonies.
- Remember that some of the microorganisms on the plates can make you sick, some of
them can be used for good things, and many are neither good nor bad.
Be sure to wash your hands after handling the petri plates!!!
Learning Center Activity 2: Microbial Zoo Worksheet
Code | Description | Suspected Source of
| (number and | Contamination
| type of colonies, |
| colors, appearance, |
| amount of growth) |
Learning Center Activity 2: The Microbial Zoo Instruction Sheets
The Microbial Zoo
- Read The Microbial Zoo-Fact Sheet.
- Examine the petri plate display.
- Use the Microbial Zoo Worksheet to note the number and variety of organizms on the
- Guess the source of contamination for each plate.
- Check your answer against the key.
- DO NOT OPEN THE PLATES!!!
- WASH YOUR HANDS AFTER HANDLING!!