Teacher Notes

Mold Testing

Student Laboratory Kit

Materials Included In Kit

3M® Petrifilm™ Yeast and Mold Count Plates, 50
3M® Petrifilum™ Yeast and Mold Count Plates (Publication No. 10166)
Mold plate spreaders, 6
Pipets, 50
Sampling tubes with caps, 50
Swabs, 50

Additional Materials Required

Water, distilled (optional)
Autoclave (optional)

Prelab Preparation

  1. Make enough copies of the Flinn publication No. 10166 handout so each student may receive a copy.
  2. Fill sampling tubes half full with distilled water.
  3. Be sure to read the publication and practice the inoculating and spreading techniques for Petrifilm plates. Prepare for your demonstration of the techniques. Grow some mold on one of the plates prior to student work and show it during your demonstration.
  4. Determine locations for sample collections. Determine if you want to test areas in the school. There is no need to create a mold scare unnecessarily! Judge the situation at your school. Students love to collect samples in unique places and unusual environments. Set guidelines based upon your experience in your location. Samples can easily be collected at home as an overnight assignment and plates inoculated in the lab the next day.

Safety Precautions

Exposed Petrifilm™ Yeast and Mold Count Plates will contain viable yeast and/or mold cultures. Do not separate or handle the plates unnecessarily. Handle the plates using sterile techniques. Use eye protection and chemical-resistant gloves. Always clean work areas and wash hands after working with microbiological materials.


Please consult the Biological Waste Disposal section in your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Even though the amount of media on Petrifilm plates is very limited, and thus restricts the volume of growth, Petrifilm plates should be handled with care. Open the plates and soak them in 10% bleach solution or autoclave before disposing according to Flinn Suggested Disposal Method #26a.

Teacher Tips

  • Enough materials are provided for 50 test plates. This provides enough plates for a class of 30 students working in pairs to run tests on three different samples plus a few for teacher demonstrations. Different classroom team organizations can allow other testing patterns.

  • Be sure to emphasize proper handling technique for the Petrifilm plates once they have been inoculated.
  • It is important to note that the techniques outlined in this kit are not a truly sterile or controlled situation. If autoclaves and sterilizing equipment are available, then sterile sampling tubes should be prepared. Test tubes should be substituted for the polystyrene sampling tubes. This would eliminate possible contamination of the distilled water in the sampling tubes. The working assumption in the activity is that the sample tube water will be the same for all samples and that any differences that result will come from the mold differences at the sample sites. Experience shows that this assumption holds up and that legitimate differences will be observed at different test sites. If this activity is conducted in a microbiology course, the additional sterilization step should be discussed and utilized in the procedure.
  • Results will vary considerably if diverse collection places are examined. Damp, moist environments will test positive for molds for sure (e.g., restrooms, kitchens, locker rooms, janitor closets). It is also likely, however, that spores will be collected in what seem to be very unlikely areas. Mold spores are truly ubiquitous and we are surrounded by them. Only when molds grow in unwanted places where humans are in confined quarters do they usually become a health hazard. Persons allergic to mold spores, however, can have reactions wherever the wrong spores appear in concentrations high enough to cause reactions. Be alert and sensitive to the possible presence of individuals in your class who may be allergic to molds.

Correlation to Next Generation Science Standards (NGSS)

Science & Engineering Practices

Planning and carrying out investigations
Analyzing and interpreting data
Constructing explanations and designing solutions

Disciplinary Core Ideas

MS-LS2.A: Interdependent Relationships in Ecosystems
HS-LS2.A: Interdependent Relationships in Ecosystems

Crosscutting Concepts

Scale, proportion, and quantity

Performance Expectations

MS-LS2-1. Analyze and interpret data to provide evidence for the effects of resource availability on organisms and populations of organisms in an ecosystem.

Teacher Handouts


Student Pages

Mold Testing


“A west suburban high school infected with toxic mold will be closed indefinitely as a safety precaution while thorough environmental tests are done there.”

4/6/2001 Chicago Sun-Times

A school costs millions of dollars? Mold is everywhere. How could this happen?


  • Mold morphology

  • Mold testing


Molds are simple microscopic organisms that play a major role in the ecosystem by helping to break down dead materials. Mold spores are nearly everywhere and actively growing molds can be found wherever growth conditions are favorable. Molds need only a few basic things to thrive—moisture, food and a surface to grow on. When a mold spore lands on such a spot, it usually starts to grow and reproduce rapidly.

Some molds are considered useful and beneficial, such as those used to make antibiotics and cheese. Other molds, however, are less beneficial to humans and may even be highly toxic. Most molds found indoors (like those in the west suburban high school) come in from the outdoors. Molds reproduce by producing very tiny particles called spores. The spores float on air currents and may reproduce indoors where they find a suitable place to grow. Free-floating mold spores are known to cause human allergic reactions, much like plant pollen causes allergic reactions associated with hay fever and the like. Mold spores cause health problems when they become airborne and are then inhaled in large quantities. Everyone is exposed to mold spores in some concentration in outdoor air. Exposure to molds indoors, however, where spores are more concentrated, is not considered healthy. Allergic individuals are particularly at risk when exposed to high levels of indoor mold spores. Symptoms of mold exposure are varied and depend on the individual. Typical reactions include wheezing and difficulty breathing; nasal and sinus congestion; burning eyes; sore throat; dry cough; nose and throat irritation; and skin irritation.

Some molds are obvious because they can be observed easily while they are growing. Wet, musty areas of the home (e.g., bathroom, basement) are often the substrate for molds. Other times molds grow beneath wall paper or behind walls and are not as obvious. Sometimes they can be growing in even harder to locate places, such as in heating ducts. Home inspectors can conduct air sampling tests to test the air for mold spores. It is possible to conduct mold-swab contact tests in areas that can be reached.


Water, distilled
3M® Petrifilm™ Yeast and Mold Count Plates
3M® Petrifilm™ Yeast and Mold Count Plates (Publication No. 10166)
Mold plate spreader
Pipet, transfer
Sampling tubes with cap

Safety Precautions

Exposed Petrifilm Yeast and Mold Count Plates will contain viable yeast and/or mold cultures. Do not separate or handle the plates unnecessarily. Handle the plates using sterile techniques. Use eye protection and chemical-resistant gloves. Always clean work areas and wash hands after working with microbiological materials.


  1. Read and study the 3M® Petrifilm™ Yeast and Mold Count Plates (Flinn publication No. 10166).
  2. Your teacher will demonstrate the use of Petrifilm Yeast and Mold Count Plates. The demonstration will include how to collect samples, inoculate the Petrifilm plates, spread the sample on the plate and incubate the plates.
  3. Secure a swab and a capped sampling tube containing distilled water. Collect a swab sample(s) as directed by your instructor. Upon returning to the laboratory, inoculate Petrifilm plates with your collected sample(s).
  4. Incubate the Petrifilm plates and observe the plates after three days and after five days. Follow the guidelines for distinguishing yeast and mold colonies found in the 3M® Petrifilm™ Yeast and Mold Count Plates publication. Count the number of colonies found on each of your sample plates.
  5. Record your observations and descriptions of each test site. Draw sketches of the various molds found at each test site.
  6. Compare mold numbers from various locations. Do the numbers correlate with the conditions found at the collection sites?
  7. Your instructor will hold a Mold Count Seminar. Be prepared to discuss these questions as a class:
  1. Was mold found at every location?
  2. Which areas had the most mold? Describe conditions at these sites.
  3. Were any of the high mold count locations where they might affect people’s breathing or health?
  4. How can mold be killed?
  5. Research molds and determine which molds are most toxic to humans.
  6. How do we prevent mold growth in foods?
  1. Consult with your instructor for appropriate disposal procedures.

Next Generation Science Standards and NGSS are registered trademarks of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.