Bioaerosols - Aerosols: Measurement, Dosimetry, and Health Effects - page 325

12.6.4.4 Immunoassays
Antibody-based immunoassays, particularly enzyme-linked immunosorbent assays (ELISA), are
widely used for the measurement of aeroallergens and allergens in settled dust, using enzymatic
reactions or radio-immunoassays (RIA) for detection. Important advantages of immunoassays
include (1) the stability of most of the measured components, allowing longer air sampling times,
and freezing of samples for storage prior to analysis; (2) the incorporation of standards; (3) the pos-
sibility of testing reproducibility; and (4) speciicity and sensitivity.
To date, the house dust mite allergens, Der p 1, Der f 1, and Der p / f 2 have been most widely
investigated and the methods have been well described. 385-387 Methods for assessment of exposure
to rodent, 388-390 cockroach, 391 and storage mite allergens 392 also have been published. Recently, a
luorescent multiplex assay was developed to measure several indoor allergens simultaneously in
one assay. 393 It is based on monoclonal antibodies that are covalently coupled to luorescent micro-
spheres. A commercially available assay kit simultaneously measures eight indoor allergens: Der
p 1, Der f 1, Mite Group 2 ( Der p 2, Der f 2, and Eur m 2, Euroglyphus maynei ), Fel d 1, Can f 1, Rat n 1
( Rattus norvegicus , rat), Mus m 1 ( Mus musculus , mouse), and Bla g 2 (Maria ™ ).
Methods for measurement of fungal allergens are not widely available due mainly to the fact
that fungal allergen production is highly variable and dependent on factors such as substrate and
temperature (Section 12.3.2.6). However, speciic immunoassays have been developed to measure
fungal glucans 213,394,395 and extracellular polysaccharides, 396 with the latter assay allowing partial
identiication of fungal genus. These assays are experimental and as yet have not routinely been
applied nor become commercially available.
12.6.4.5 Chemical Assays
Chemical analyses for bioaerosols have gained expanded utility with the development of increas-
ingly sensitive instruments that allow analysis of smaller amounts of material. Because preservation
of cell viability is not an issue in chemical assays, a wider variety of methods and longer sampling
times can be used to collect bioaerosols.
The cell walls and membranes of fungi and bacteria contain unique chemical components by
which they can be identiied and quantiied. 397,398 These compounds include lipids and various pro-
teins and peptides, peptidoglycan in bacterial cell walls, teichoic acid in the thick peptidoglycan
layer of Gram-positive bacteria, LPS in the outer membranes of Gram-negative bacteria, and ergos-
terol in the cytoplasmic membranes of fungi. Aerosolized toxins and volatile metabolites also can
be analyzed by standard chemical methods.
Cellular fatty acids are commonly used to identify bacteria after they have been grown in cul-
ture. For example, tuberculostearic acid, a component of lipoarabinomannan in the cell walls of
coryneform bacteria (e.g., Mycobacterium , Rhodococcus , and Corynebacterium species), readily
can be analyzed by GC. 397 Fatty acid analysis also has been use for house dust and air samples. 174,399
The beneits of these assays are that they address biomass; the drawbacks are the costs of the
analyses, overlapping of agent proiles, questions in conversion of biomass to cell counts, and pos-
sible compositional shift from variance in growth conditions. 174 Chemical LPS analysis is generally
based on detection of 3-OHFA by high-performance liquid chromatography (HPLC) or GC-MS. 400
Chemical analysis of endotoxin has the advantage of being insensitive to variations in biological
activity, but these techniques are two to three orders of magnitudes less sensitive than the LAL
assay (Section 12.6.4). 263
Ergosterol is a principal sterol in the membranes of fungal hyphae and spores and has been used
to measure fungal biomass. One speciic drawback to ergosterol analysis is that it is not species
speciic. Ergosterol is stable in air-dried conditions and can be extracted in basic aqueous methanol
followed by microwave heating and analysis by HPLC, GC, GC-MS, or MS/MS. 399,401,402
VOC proiles also show a potential for identiication of environmental microorganisms (Section
12.3.2.5). Air samples collected on sorbent material and analyzed by thermal desorption-GC and