Evaluation of test-chamber and validation of different sampling and analysis methods for bioaerosols

Status:

completed 12/2015

Aims:

The aim of the project was to develop a bioaerosol calibration system which should allow the generation and constant supply of bioparticles with defined concentrations and viability evenly over the whole testing volume for a direct comparison of bioaerosol samplers under controlled and standardized conditions.

Activities/Methods:

The project team together with PALAS GmbH conceived and built a bioaerosol chamber in which these parameters can be strictly met even when bioaerosol sampling devices are operating inside the running calibration chamber. Physical validation of the system was carried out with inorganic particles and the results of this validation, published in "Air Quality Control" in 2013, clearly showed that, using low-velocity laminar flow, the strict requirements defined at the beginning, are met. In particular, even particle distribution and negligible influence of operating sampling devices was demonstrated.

The biological validation started with the development of Standard Operation procedures for the production of standardized bioaerosol types encompassing 8 different fungal species, two bacterial and one viral specimen. Five control points were implemented including aerosolization (concentration and viability each before and after the nebulizer), transport (particle counter) and sampling (MAS-100-NT sampler for validation purpose). The results of this validation runs showed that all required biological parameters can be controlled and that this test system is suitable to quantitatively determine the biological sampling efficiency of a given sampler. Next, 7 different samplers representing 4 different sampling principles were compared under the determined chamber parameters in repetitive experiments. Sampler efficiencies were compared by classical microbiological methods (colony forming units-based viable counts) as well as microscopically and by molecular-biological methods. Both of the latter allowed also the determination of the non-viable portion of bioparticles collected by the different sampling devices. Some sampling systems were tested also for their ability to collect and display pyrogenic bioparticles.

Results:

Viability-based analyses showed that in average samplers detected around 50% of all viable fungal or bacterial spores in the test air and taking into account a roughly 50% germination rate of such spores, the overall detection capacity for these specimens was around 20% of all spores present in the controlled environment. An up to three-fold deviation between different samplers was observed. More sensitive microbes such as yeast cells or gram-negative bacteria had an even much higher rate of deviation between sampling systems in which impingement were superior over other collection principles. Although molecular-biological systems allowed the detection of also non-viable microbes, the low DNA extraction efficiency from fungal spores led to a generally low sensitivity of the method which clearly needs improvement before it can be used to quantitatively determine fungal cells in aerosols. Summarizing the data obtained in this project allowed to present a guideline of which methods and sampling systems may be best suitable and thus be recommended when as certain type of bioaerosol component has to be analyzed.

The project and its results were presented at a meeting held in Vienna and Tulln organized by the project team composed of personnel from the funding bodies and the research institutions. International experts were discussing our data and their own work during this workshop and from the in-depth discussions it became fairly clear that the possibility to quantitatively determine the biological sampling efficiency of bioaerosol samplers will certainly influence and improve the assessment of bioaerosol loads by health authorities in outdoor and indoor settings.

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