Effective Collection of Airborne Micro-Organisms by Direct Impaction on Silicone Sealants—Comparison of Different Adherent Surfaces

Abstract

For effective sampling of airborne micro-organisms different techniques such as impingement, filtration and impaction are commonly used. Impaction is the method which allows best for direct collection on adhesive surfaces for immediate microscopic analysis. The efficiency of collection largely depends on the quality of the sampling surface to retain particles. This article compares the suitability of some traditional and new adhesive coatings to collect and retain airborne micro-organisms efficiently for subsequent fluorescence microscopy. Sacharomyces cerevisiae yeast cells were aerosolized in a test tubing system in the laboratory. Samples were collected by a round jet impactor in a defined round deposition area on glass slides coated with different adhesive materials. Particle distribution in the deposition area and collection efficiency as well as particle losses were estimated. Fluorescent staining with Mycoval and DAPI was used to quantify the amount of collected cells and cell losses due to the staining procedure. Filtration was taken as reference system. The collection efficiency of the tested adhesive surfaces ranged from 2 to 97%. Silicone sealants showed with 97% the highest collection efficiency. All particles were located in the central region of the deposition area. Cell losses due to the staining procedure were very small (<1%) and no background fluorescence was observed after DAPI staining. Even after sampling times of 45 min the collection efficiency was still above 90%. Longer collection (>50 min) resulted in increasing cell losses. Collection efficiency was little influenced by relative humidity of the air between 20% and 100%.

Comparison of Different Fluorescence and Non-Fluorescence Staining Techniques for Rapid Detection of Airborne Micro-Organisms Collected on Room Temperature Vulcanizing (RTV) Silicones from Generated Aerosols and from Ambient Air

“…Most suitable for our purpose was 1 component "RTV" silicones, which cure by reaction with atmospheric moisture. In this group, the "Sista Küchensilikon" had the highest retention efficiencies in previous experiments (Clauß et al 2010). It has an acetic curing system and releases small amounts of acetic acid during the curing process (25 µg/mg; personal communication, Analyze Inc., Chandler, AZ, USA, May 2010).…”

“…Suspensions of micro-organisms or particles in distilled water were sprayed in the air stream of a laboratory-based aerosol test tubing system, which was described in detail by Clauß et al (2010). In general, it is constructed of 125 mm Ø KGB PVC pipes and stainless steel boxes.…”

“…Out of 30 different tested adhesive coatings, "single component room temperature vulcanizing" (RTV) silicones were the most efficient showing collection efficiencies up to 97%. Furthermore, cell losses and background fluorescence were negligible when the coated slides were used within 50 min after preparation and a standardized staining procedure with 4 ,6-diamidino-2-phenylindole (DAPI) was applied (Clauß et al 2010). However, these results were gained by testing 1 species of micro-organisms and 1 staining method and little is known how these sealants are reacting with other types of micro-organisms such as molds and bacteria.…”

Recent Advances in Monitoring, Sampling, and Sensing Techniques for Bioaerosols in the Atmosphere

“…Microorganisms collected by a sampling system should not be subjected to extreme environmental conditions, disinfectants (e.g., chlorine or alcohol), and/or high-speed impaction onto the sampler. 43 In addition to the sampling approaches, bioaerosol sensing is critically dependent upon various limiting factors such as the selection of appropriate temporal interval, low biomass, and preservation of the in situ state during sampling, storage, and preservation. 44 For instance, environmental factors (such as relative humidity, temperature, and wind conditions) may considerably vary with the time of the day, the season, and the weather conditions.…”

“…To represent genuine levels of exposure to the pathogen, special consideration should be given to maintaining a viable count of the samples in the culture. Microorganisms collected by a sampling system should not be subjected to extreme environmental conditions, disinfectants (e.g., chlorine or alcohol), and/or high-speed impaction onto the sampler …”