Black-crowned night heron.

Microbes & Indoor Air Quality
An Environmental Project
Christine L. Case

  BIOL 215   My home page

Sick Building Syndrome | Lab Protocol | References | Data


  Lab Protocol
Use the impaction-type MicroBio air sampler to inoculate nutrient media. Some general guidelines for sampling and cultivation are described here.

Air Sampling

When to sample:

  • Visual evidence of biological contamination

  • Complaints after water damage

  • Different times of day

  • When ventilation is on (check for air flow)

How much to sample:

  • Take 5 to 10 samples from each test area

  • Sample 100 to 1000 L of air/sample. Caution: exposing one plate for >5 min could desiccate cells already trapped on the plate.

Where to sample:

  • Complaint area

  • Outdoors (control)

  • Noncomplaint area (control)

What to look for:

  • Ventilation system

  • Windows

  • Doors to outside

air sampler
Instruction manual

To cultivate fungi:
Inoculate Sabouraud dextrose agar (SDA)
Incubate 3-7 days at 20-25°C

To cultivate bacteria:
Inoculate trypticase soy agar, nutrient agar (NA)
Inoculate 1-2 days at 28-35°C

Count the colony forming units (CFU). For statistical accuracy, plates with between 25 and 250 colonies are used.

Calculate the CFUs/volume of air sampled.

Fungi can usually be identified by macroscopic and microscopic appearance.

Bacteria can be classified by gram reaction.

  When are results meaningful?

  1. If fungi are more than half of the outdoor counts.
  2. If there is a significant difference between indoor and outdoor counts.
  3. If common fungi> 300 cfu/L.
  4. If other fungi> 150 cfu/L.