10th International Aerosol Conference
September 2 - September 7, 2018
America's Center Convention Complex
St. Louis, Missouri, USA

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Liquid Air Sampler Bias on Bacterial Biodiversity

JOANIE LEMIEUX, Marc Veillette, Nathalie Turgeon, Caroline Duchaine, CRIUCPQ, Université Laval

     Abstract Number: 407
     Working Group: Bioaerosols

Abstract
Air samplers are essential in bioaerosols study in order to concentrate and analyze the microbial content of the air. In some environments and circumstances, the air can be highly charged with bioaerosols and can contain pathogenic microorganisms such as bacteria, molds and viruses. Bioaerosols can cause diverse illnesses to exposed individuals. Obviously, field sampling is mandatory for exposure assessment studies.

Preliminary data from our laboratory showed a drastic underestimation of biodiversity (microbiota) obtained with a liquid sampler compared to sampling with electrostatic filter (Veillette & al., American Society for Microbiology General Meeting-Microbe 2017). A considerable bias may be inherent to the use of different types of air samplers, even when used side-by-side in a single environment. There are two possible hypotheses to explain this divergence in biodiversity obtained: preferential re-aerosolization and preferential sampling.

This study aims at studying preferential re-aerosolization after capture, that is defined by the tendency of a given microorganism to be lost during liquid evaporation occurring while liquid sampling with SKC Biosampler© (SKC Inc.). To study this phenomenon, SKC Biosampler© collection liquid (20 mls) was spiked (n=15) with known concentration of two bacterial strains (Pseudomonas aeruginosa and Staphylococcus aureus), in known proportions. The fate of the spiked bacterial mix during sampler operation was then followed (before and after 15 minutes, 12.5 L/min sampling). The evaporated liquid (2 mls) content was also captured using a filter (SKC 37 mm closed face cassette, 0.4 µm polycarbonate filter), at the exhaust, between the pump and the sampler. DNA was extracted from SKC Biosampler© liquid samples (before and after) as well as from the cassette filter and specific qPCRs were performed. Pseudomonas/Staphylococcus ratios were then compared throughout the experiment.

When looking at the relative ratios (RR) of Pseudo/Staph in the after samples and in the before samples :

1 RR P+S, a/b = (PseudoAfter/StaphAfter) /(PseudoBefore /StaphBefore)

we demonstrated that Pseudomonas proportion increases with the use of the sampler (is enriched in the remaining collection liquid) whilst Staphylococcus proportion decreases in the remaining liquid.
Consequently, the respective ratios (R) of Staphylococcus and Pseudomonas in the exhaust-connected filter and in the before samples:

2 R S, f/b = StaphFilter / StaphBefore

and

3 R P, f/b = PseudoFilter / PseudoBefore

showed that Staphylococcus is 4.1 times more enriched in the exhaust-connected filter than in the before liquid (is lost in the remaining collection liquid) when compared to Pseudomonas ratio (R S, f/b = 0.0118 and R P, f/b = 0.0029).

Then, when comparing the relative ratios of Pseudo/Staph in the after samples and in the before samples1 (RR P+S, a/b) to the relative ratios of Pseudo/Staph in the exhaust-connected filter and in the before samples :

4 RR P+S f/b = (PseudoFilter/StaphFilter) / (PseudoBefore / StaphBefore)

we are able to affirm that Pseudomonas is concentrated in the liquid sampler through sampling while Staphylococcus as a tendency to be re-aerosolized from the sampler.

Other bacterial strains are being studied to better understand the factors influencing the preferential loss observed. This project showed a different pattern of loss and concentration of two bacterial species, starting to solve the puzzle on the bias involved in liquid air sampling.