Strategy for Air Sampling for Culture-based Analysis

Jan. 12, 2009 - PRLog -- Information on the presence of culturable molds may be a possible indication of active growth in indoor environments. Active growth in indoor environments needs to be addressed, and the source needs to be detected immediately to stop further contamination. The presence of culturable molds in indoor environments implies not only the presence of allergens and mycotoxins, but potentially also pathogens that may cause disease, especially in people with compromised immune systems. Detection of culturable organisms in the air is performed by impacting air samples directly onto culture media. Unlike direct microscopy, this method provides quantitative and qualitative data on the specific genera and/or species present in the indoor air.

This method is usually performed using one of the most common type of samplers are the vacuum pump and an Andersen single-stage viable impactor. Air is drawn through the pump calibrated to a flow rate of 28.3 liters per minute and, by the inertia principle, particles are impacted onto 90mm Petri dishes containing specific agar. The type of media used in the Petri dishes varies depending on the purpose of the investigation (mold, bacteria, or specific genera).  After the sampling, the plates are sealed with laboratory film and labeled in conjunction with the sample number and information on the COC form. The agar plates are sent to the laboratory, where they are incubated at 25°C for a specified period, usually 4-5 days for mold species. At the end of this period, laboratory analysts quantify and identify (to the species level, if so desired) most organisms that have grown on the media.

To ensure the quality of data, the samples should be transported overnight to the laboratory. If sample storage is required prior to shipping, they should be refrigerated at 4°C for no more than 24 hours. Samples should be packed with artificial ice packs and/or in coolers to avoid extreme temperature during shipping, or prolonged holding time, may change the population of the microorganisms to be tested.

Generally for routine analysis of a wide spectrum of environmental fungal species, Malt Extract Agar (MEA) and/or Potato Dextrose Agar (PDA) are recommended.

Advantages of this technique are:

Allows for the differentiation of Penicillium and Aspergillus type spores.
Allows for the identification of spores to the species level.
Provides counts indicative of how many spores are viable and present in the air.  This is especially important for immunocompromised individuals who would be more susceptible to the infections that viable spores may cause.

Disadvantages of this technique are:
Long turnaround times. It takes 7-10 days for the mold spores to grow on the media.
Because culturable samples are only capable of growing viable and healthy mold spores, this method may not give you an accurate measurement of the indoor air quality in the building.  That is, non-viable mold spores will not be found in culturable samples that can be allergenic, oxygenic, and/or irritants..
Total numbers may be misleading, since fast growers may overgrow the medium and mask the presence of slow-growing organisms.
The technique will also miss those organisms that do not grow on culture media, or that may need a specific medium.

To learn more on the sampling strategy for air sampling, please visit http://www.iaqsg.com/air-sampling-for-culture-based-analy...

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