Environmental Engineering Reference
In-Depth Information
Figure 9.8
Andersen single-stage bioaerosol sampler.
is that only viable particles can grow on collection media. In most cases,
culturable/viable bioaerosol particles represent only a fraction of the total
bioaerosol concentration in air. In the case of mold spores and particles, the
number of total spores and particles averages 10+ times greater than the
culturable/viable concentration. Differences can vary from several times to
orders of magnitude higher. Apparent viability ratios vary from genus to
genus, with viabilities ranging from <1% to >20%. In the case of bacteria,
the ratio of culturable/viable to total particles may be 1% or less.
The viability of airborne bacteria and mold spores is determined by
environmental stresses they are subject to during dispersal. These include
desiccation and exposure to ultraviolet light. Though microbial particles may
not be viable, they may nevertheless have considerable biological and med-
ical significance. In the case of mold spores and hyphal fragments, nonviable
and viable particles have similar antigenic properties.
Viable airborne microbial particles differ in their culturability on the
various media formulations used in sampling. Apparent collection efficiencies
for different organisms vary from one medium to another. The use of malt
extract agar (MEA) and tryptocase-soy peptone agar have been recom-
mended for general purpose use for mold and bacteria (including thermo-
philic actinomycetes), respectively. Malt extract agar appears to provide good
results for a wide variety of fungal species, particularly those with high water
activities. There is increasing use of diclorvan-glycerol agar (DG-18) for sam-
pling xerophilic mold genera and species such as
Aspergillus,
and cellulose-
amended agar for sampling
Stachybotrys chartarum
. For xerophiles, higher
colony counts have generally been reported on DG-18 as compared to MEA.
2. Total spore and particle sampling
Total spore/particle sampling methods and devices are less widely used
than culturable/viable methods described above, and their use has been, for
the most part, limited to mold. This reflects the historical early development
