How long should TSA be incubated for Active (Viable) Air Sampling?

For Active (Viable) Air Sampling using Tryptic Soy Agar (TSA), the incubation time of 48 to 72 hours is appropriate for a couple of reasons. This timeframe allows for the growth of a wide variety of microorganisms that may be present in the sampled air. By incubating for this duration, potential contaminants, including bacteria and fungi, have enough time to grow into colonies that can be counted and assessed.

Incubating for less time, such as 24 hours, may not capture organisms that have longer generation times or those that are slower to grow. On the other hand, a longer incubation time, such as 5 to 7 days, could lead to overgrowth or the possibility of non-viable organisms remaining from those that were alive when the sampling was taken, creating a false reading of microbial presence. Therefore, the 48 to 72-hour incubation span strikes a balance between allowing sufficient growth while ensuring accurate representation of viable air microbial contamination.