Culturable air sampling is one of the most common methods of volumetric air sampling. The sampler works by drawing measured volumes of air through an instrument that contains a petri dish (or dishes) with culture media. Spores that impact onto the plate are then allowed to incubate and grow, after which the colonies may be counted and identified.
A general philosophy regarding the interpretation of biological air samples is formed primarily by two guiding principles. First, an effective interpretation is based on the comparison of indoor and outdoor samples. There are currently no guidelines or regulations to indicate “safe” or “normal” spore levels, however, we typically expect indoor counts to be 30 to 80 percent of outdoor spore counts, with the same general distribution of spore types present. And second, variation is an inherent part of biological air sampling. The presence or absence of a few genera in small numbers should not be considered abnormal.
Culturable air sampling allows for the differentiation of Aspergillus and Penicillium (speciation when required). It also provides counts indicative of how many spores are viable and present in the air. It can also be used to provide a bacterial count.
Culturable air sampling methods require that the spores in the air are alive, survive the sampling process, germinate on the sampling media, and compete well with other species present on the growth media. Culturable air sampling does not indicate the presence of non-viable spores, which may also be capable of producing allergies or irritation. Culturable air sampling also requires five to seven days for incubation after the sampling has taken place.
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