Microorganisms are always around and ready to contaminate your carefully grown cultures. In this practical we will determine what common airborne contaminants look like. This makes it easier to identify them when they pop up on your plates later on


  • 1 Peptone agar (PA) plate, favourable to bacteria
  • 1 Malt agar (MA) plate, favourable to yeast and fungi

In case you have no clue how to make Agar plates, please take a look at the Microbiology at Home manual of Dr. Simon Park or follow our BHA Microbe Cultivation Manual. You will need a pressure cooker to sterilize the mediums.


  1. Find an interesting spot in the building, preferably in the room that you are going to conduct the experiments
  2. Remove the lid from the plates and leave the plates for 30 minutes.
  3. Collect the plates.
  4. Incubate at 30° C for 24h.
  5. Inspect your plates and look at them under the microscope.

Additional test

You can also use this method to test whether your sterile hood works properly. Turn on the sterile hood and open up 2 plates in front of it for 30 minutes. Incubate and watch the results. The plates should be sterile, with no colonies or fungi growing on it.

Some example outcomes

Back to BHA6 - Class 2