Sampling, extraction and measurement of bacteria, endotoxin, fungi and inflammatory potential of settling indoor dust

Abstract

Selection of sampling device, sampling location and period are important first steps in the measurement of exposure to bioaerosols in indoor air. The steps following the sampling include treatment of samples and laboratory analysis. In this study, settling bacteria, endotoxin, fungi and serine protease have been measured in Danish homes using Electrostatic Dust Fall Collectors (EDCs). The effects of the presence of occupants, sampling on open surfaces versus in bookcases and treatment of samples have been studied. Concentrations of bacteria and endotoxin were significantly higher when occupants were at home than when they were absent. Across homes, higher concentrations of fungi were found in spring than in winter, as was the total inflammatory potential, while higher concentrations of protease were found in winter than in spring. The placement of the EDCs in bookcases versus on an open surface significantly affected the measured concentrations of bacteria and endotoxin. Direct extraction of EDC cloths caused a higher measured concentration of bacteria, fungi and serine protease than if EDC cloths were extracted post-storage at -20 °C. Extraction of EDC cloths caused an average of 51% and 58% extraction of bacteria and fungi respectively. In conclusion, EDCs should be placed on open surfaces during the sampling, how much occupants are present in their home during sampling and sampling season should be considered, EDC cloths should not be stored in a freezer before extraction of microorganisms, but extraction suspensions can be stored at -80 °C without affecting the number of microorganisms significantly.

Impact of dwelling characteristics on concentrations of bacteria, fungi, endotoxin and total inflammatory potential in settled dust

“…In another study differences in endotoxin exposures have been found when occupants were absent from their home for two weeks. During occupancy the levels of endotoxin were 650 EU m À2 day À1 while during occupant absence the levels dropped to 39 EU m À2 day À1 (average values) [35]. Thus, the presence of occupants seems to increase the concentration of airborne endotoxin considerably.…”

“…However, studies comparing the indoor and outdoor levels of bacteria often find the indoor/ outdoor ratios are above 1 [2,6,21,34,52], showing the importance of indoor sources. Several studies have suggested that in environments like homes [35], university buildings [37], schools [6] and day-care centers [4], the main source of airborne bacteria indoors are humans and human activities. Bacterial exposure levels in homes are influenced by many factors, including, for example, relative humidity of indoor air and seasons during the year [22,44].…”

“…The Electrostatic Dust fall Collector (EDC) has been used for sampling sedimenting microorganisms and other particles including endotoxin in the indoor environment [35]. The EDC was chosen for this study because of its time integrating sampling ability, which is important given that indoor exposure varies during a day due to different activities and occupancy levels [35] and the opening of windows [34]. The ability of collected dust samples to induce ROS production was evaluated by quantifying the TIP of settled dust.…”

“…The detailed procedure and evaluation of TIP (TIP m À2 day À1 ) of settled dust is described in Refs. [35,57]. The Electrostatic Dust fall Collector (EDC) has been used for sampling sedimenting microorganisms and other particles including endotoxin in the indoor environment [35].…”

“…Due to space constraints, in seven dwellings the EDC was placed not on the top of the bookshelf but between bookshelves. The average height of EDC locations was 1.83 ± 0.23 m. Fungi, endotoxin and bacteria present in the dust on the EDCs were extracted and quantified as described elsewhere [35].…”