DEVELOPMENT OF A SAMPLER FOR THE RAPID ANALYSIS OF BIOAEROSOLS
Creators: name: Liao, Li
Publisher: name: Purdue University Graduate School
Year: 2021
Subjects: Occupational and workplace health and safety

description: Airborne biological aerosols (also called bioaerosols) including pathogens are found in various occupational and environmental settings. To protect human health and the environment, the first step is assessing the exposure levels of bioaerosols in the fields where the sources of bioaerosols are located. However, the conventional methods to assess the level of bioaerosols are not ideal in the field due to their delayed analysis times. To overcome these limitations, faster and convenient analysis methods are required. In this study, a size-selective bioaerosol sampler was developed and combined with two swab-based analysis methods: 1) adenosine triphosphate (ATP) bioluminescence assay for measuring the total bioaerosol concentration and 2) immunochromatographic assay (ICA) for identifying specific pathogenic bioaerosols. The size-selective bioaerosol sampler was developed and tested in the laboratory. Specifically, the bioaerosol sampler consisted of a size-selective inlet to remove the particles larger than target size, an impactor to collect bioaerosols onto the head of a swab used for both ATP bioluminescence assay or ICA, a swab holder, and a sampling pump. An impactor nozzle was designed based on a theoretical model. The collection efficiency of the fabricated impactor was tested using aerosolized sodium chloride particles and then the particle diameter corresponding to the collection efficiency of 50% (cut-off diameter, d<sub>50</sub>) was evaluated. The experimental d<sub>50</sub> was 0.44 µm which means the bioaerosol sampler can theoretically collect most bioaerosols.In the study measuring the total bioaerosol concentration, the size-selective bioaerosol sampler was used with the ATP bioluminescence assay. First, test swabs were calibrated by comparing with the colony counting methods. Specifically, correlations between ATP bioluminescence (relative light unit; RLU) from commercially available swabs having different sensitivities and colony forming unit (CFU) were examined using <i>Escherichia coli</i> (<i>E. coli</i>) suspension, and then the conversion equations from RLU to CFU were obtained. From the correlation results, the R<sup>2</sup> values of the two swabs were 0.53 for the normal swab and 0.81 for the sensitive swab, respectively. The conversion equations were the linear function and the slopes of the normal and sensitive swabs were 633.6 and 277.78, respectively. In the laboratoryand field tests, the size-selective bioaerosol sampler with ATP bioluminescence assay and a conventional Andersen impactor with colony counting method were compared. In the laboratory tests, concentrations of aerosolized <i>E. coli</i>collected using the size-selective bioaerosol sampler were highly correlated to those from the Anderson impactor (R<sup>2</sup> = 0.85). In the field tests, the concentrations measured using the bioaerosol sampler combined with ATP bioluminescence assay were higher than those from the Andersen impactor with colony counting method due to the limitations of the latter approach. In the study identifying pathogenic bioaerosols, <i>Legionella pneumophila</i> (<i>L. pneumophila</i>) was used as a target pathogen. Prior to combining the size-selective bioaerosols sampler and ICA, the lower limit of detection of the lateral flow test kit used in the ICA was determined. In the conditions of this study, the lateral flow test kit formed a positive line when more than 1.3 × 10<sup>3</sup> CFU of <i>L. pneumophila</i> were on the sampling swab. In further experiments, <i>L. pneumophila </i>suspension was aerosolized and then collected using two identical bioaerosol samplers having different sampling times (10 and 20 min) to estimate the concentration. Andersen impactor with colony counting method was also used for measuring the concentration of <i>L. pneumophila</i> and the comparison with the developed methods. The developed method successfully collected and detected aerosolized <i>L. pneumophila</i> compared to the Andersen impactor with colony counting method. These findings confirm that the developed bioaerosol sampler combined with swab-based analysis methods can overcome the limitations of conventional methods and allows for more rapid, inexpensive, and accurate assessments for bioaerosols in the field. These methods can be immediately used in various environmental and occupational settings.