scope:

The present guideline describes an evaluation method for quantification of microorganisms by microscopic particle count after staining of DNA containing structures (DNA: deoxyribonucleic acid). It is a matter of a cultivation-free method that enables evaluation of samples that have been collected, for example, after the guidelines VDI 4252 Part 2¹⁾ and VDI 4252 Part 3 for ambient air measurements or VDI 4257 for emission measurements. Both living and dead microorganisms are measured by the cultivation-free method. Application of this verification procedure is recommended especially in cases where microorganisms are exposed on their way from the emission source to the sampling location to a special degree to environmental impacts that are hostile to life, e.g. the impacts of heat, radiation, drought or mechanical stress, with the result that microorganisms can no longer be cultivated or a distinctly reduced cultivability must at least be assumed. A differentiation of the microorganisms is not possible with this method. The application of this method requires that the operators are principally capable of distinguishing between air borne biogenic particles such as bacteria, spores, hyphae, pollens or trichomes on the basis of morphological criteria.

This guideline is designed for a concentration range starting from an order of magnitude of GZZ = 10⁵ cells/m³ (GZZ - total cell count) for sampling with impingers at an air sampling volume of 0,5 m3. Larger air sampling volumes are required in case of anticipated lower total cell count. That can be achieved by means of filtration methods with polycarbonate filters1) (see Table 2, Section 9.4).