What Lives in the Air Conditioner?

4.2 based on 28 ratings

Updated on Jul 10, 2013

Grade Level: Elementary School; Type: Biology


Air pollution is a major issue in urban environments. In this experiment, students will grow out the bacteria that collect on air conditioner filters and determine whether there are also bacterial invaders, in addition to chemical pollutants.

Research Questions:

  • Do air conditioner filters collect bacteria?
  • How long can bacteria survive on an air condition filter?
  • What implications does your experiment have for the bacteria found in an air-conditioned house?
  • What is the difference between a Sabouraud agar plate and a regular one?


  • Two sterile Sabouraud agar plates (found online or from specialty supply houses)
  • Two regular agar plates (found on line or from specialty supply houses)
  • New air conditioner filter
  • Used air conditioner filter
  • Tape
  • Forceps or tweezers
  • Sharpie marker
  • Scissors
  • Rubbing alcohol
  • Camera

Experimental Procedure #1

  1. Wash your hands thoroughly.
  2. Label the bottom of the Sabouraud plates “S Used” and “S New.” Label the bottom of the regular agar plates “R Used” and “R New.”
  3. Wipe down your scissors and forceps with alcohol.
  4. Holding the dirty air conditioner filter with the forceps, cut two 1” squares from the dirtiest part of the filter. Place one l of these pieces in the center of the Sabouraud agar plate and the other in the center of the regular agar plate.
  5. Repeat step #3, using the clean air conditioner filter.
  6. Incubate all the plates in a warm area of the house where the temperature does not change much.
  7. Inspect the plates every day, making notes about your observations. Count the number of colonies of bacteria found in each plate. Take photos of the plates.

Experimental Procedure #2

  1. Repeat experiment #1, using a dirty air conditioner filter from an air conditioner that has been turned off for several months.
  2. Compare the number of bacterial colonies found on the dirty filter in experiment #1 with the number found on the dirty filter in experiment #2. Consider how long bacteria live on air conditioners.

Terms/Concepts: bacteria, fungi, air pollution, bacterial life cycle.


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