Environmental Health Criteria 214
Environmental Health Criteria 214
Environmental Health Criteria 214
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HUMAN EXPOSURE ASSESSMENT<br />
9.5.1 Air sampling for bacteria<br />
Most of the air sampling devices listed in Table 32 can also be<br />
used for bacteria. The most widely used devices for bacteria include<br />
multiple-hole impactors, centrifugal impactors and slit-to-agar<br />
impactors, provided with collection media suitable for viable<br />
bacteria. For sampling airborne viable bacteria, the same limitations<br />
apply as for viable fungal particles. Thus, the results, both<br />
quantitatively and qualitatively, will depend on the sampling device<br />
and collection medium used. A single air sample has only a low<br />
predictive value for exposure over time (EC, 1993). Media that collect<br />
viable bacteria include tryptone soya agar, tryptone yeast glucose<br />
agar, soybean casein digest agar, and nutrient agar (EC, 1993; ACGIH,<br />
1995). To prevent fungal growth, a suitable antimycotic may be used<br />
(e.g., cycloheximide). For specific groups of bacteria, selective<br />
media could be employed, such as half-strength nutrient agar for<br />
thermophilic actinomycetes.<br />
9.5.2 Dust sampling for bacteria<br />
The sampling of settled house dust for bacteria can be conducted<br />
in exactly the same way as for house dust mites and their allergens<br />
(see section 9.2.2).<br />
9.5.3 Available methods of analysis for bacteria<br />
Air samples obtained with sampling devices collecting total<br />
bacteria can be analysed by direct examination. Samples collected on<br />
culture media have to be inoculated to obtain counts of viable<br />
bacteria. Dust can be plated either directly on to a culture medium or<br />
suspended and diluted prior to plating. Dust can also be analysed for<br />
total bacteria counts. Furthermore, an assay is available to measure<br />
endotoxin content of (airborne) dust. Gram-negative bacteria contain<br />
endotoxins as integral components of their outer membrane. Endotoxins<br />
are potent biological agents.<br />
9.5.3.1 Total count of viable and non-viable bacteria<br />
Total counts of bacteria, with some information on shape, can be<br />
obtained from some samples, for example, water and air, using<br />
epifluorescence microscopy (most commonly, with acridine orange). This<br />
method becomes less reliable as the amount of debris in the sample,<br />
both organic and inorganic, increases. More detail on bacterial shape<br />
is obtained using a scanning electron microscope but quantitative<br />
results are less reliable. Filter samples can also be used to obtain<br />
counts of viable bacteria, with subsequent taxonomic differentiation<br />
if desirable (using Gram staining and other biochemical tests). Filter<br />
samples can be analysed for endotoxin as well (see below).<br />
9.5.3.2 Viable bacteria<br />
<strong>Environmental</strong> samples are usually incubated for 2-7 days at 25°C<br />
or 37°C. For bacteria, as with fungi, the incubation temperature<br />
affects the recovery. Most environmental bacteria grow well between<br />
20°C and 30°C, and more species were recovered with incubation at 20°C<br />
than at 37°C (Hyvarinen et al., 1991). Therefore, it is recommended<br />
that plates be incubated at room temperature (20-25°C) and examined<br />
daily for several days (EC, 1993). For isolation of human pathogenic<br />
organisms, plates can be incubated at 37°C, and for thermophilic<br />
http://www.inchem.org/documents/ehc/ehc/ehc<strong>214</strong>.htm<br />
Page 165 of 284<br />
6/1/2007
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