Re-aerosolization in liquid-based air samplers induces bias in bacterial diversity

Abstract

Bioaerosols collected in a liquid-based sampler can be re-aerosolized into the airflow during collection and lost or concentrated in the collection fluid and overestimated during the subsequent analyses. Very little information is available concerning the specific impact on bioaerosol quantification and diversity and wrong evaluation of pathogens or potentially harmful microorganisms concentration could lead to incorrect data interpretation and inaccurate exposure risk assessment. The aim of this two-part study was to better understand how evaporation impacts the results obtained from liquid-based samplers. Bacterial consortium was spiked in the collection vessels of the Coriolism V R and the BioSampler V R and the bacterial concentration was monitored after running the samplers in vitro. Relative ratios of the bacteria were analyzed using qPCR (before/after). A field study in which liquid-based air samplers in a natural environment were compared to filter-based samplers was performed. This allowed for the relative characterization of either concentration or the re-aerosolization between the two samplers using high throughput sequencing methods. Amongst the four strains of bacteria examined in vitro, results suggest differential behavior between concentration or re-aerosolization from the liquid. Re-aerosolization of bacteria is difficult to predict as the cell-surface hydrophobicity, the liquid-based air sampler and its flowrate can influence it. The sequencing results from field samples confirmed the loss of entire genera by re-aerosolization (Brevundimonas, Clostridium, Mycobacterium, and Smithella) out of the BioSampler V R while concentration of several other genera were reduced (Bradyrhizobium, Delftia, Propionibacterium, and Sphingomonas). These observations suggest that evaporation in liquid samplers might lead to over-or underestimation of the prevalence of some genera.

Performance evaluation of high-volume electret filter air samplers in aerosol microbiome research

“…Some distinct differences were nevertheless observed at the species level. Previous air sampler comparisons have shown conflicting diversity patterns [ 3 , 23 , 39 ], which could partially be attributed to differences in aerosol collection and sample recovery principles. Without a common consistency and understanding of how differences between methodologies arise, it is difficult to establish an aerosol microbiome baseline for real-world environments.…”

“…Another concern with evaporation of sampling medium is reaerosolization of collected particles [4,22]. A recent study has shown that non-random reaerosolization of certain taxonomic groups in liquid samplers can introduce substantial bias when investigating microbial diversity [23]. Also, both Lemieux et al [23] and Mbareche et al [3] have reported a significantly higher microbial diversity with the use of an electret filter sampler compared to a wet cyclone sampler when sampling side-by-side in real-world environments.…”

“…The electret filter technology has recently received increased attention [3,[23][24][25][26][27][28], and has also been used in aerosol microbiome studies utilizing direct SMS [14,16]. The technology relies on low pressure-drop microfibrous filters where each fiber has an electric field frozen into it.…”

Field sampling of indoor bioaerosols

“…One study has suggested that assessing the microbial diversity of bioaerosols with filter-based high-flow rate air samplers may allow a higher diversity coverage than liquid-based high-flow rate air samplers when applying bacterial and fungal amplicon-based high-throughput sequencing approaches (Lemieux 2019; Mbareche et al 2018). This is possibly because the collection media in the liquid cyclonic impactors may be subject to evaporation depending on the environment and the relative humidity.…”

Ozone inactivation of airborne influenza and lack of resistance of respiratory syncytial virus to aerosolization and sampling processes

“…However, since it the aerosol path (nebulizer-up to five diffusion dryers-chamber), particles could be lost by diffusion. As for the SKC BioSampler, this device preserves the virus infectivity and has a great collection efficiency of 1 μm particles but the re-aerosolization phenomenon has previously been documented [44]. While all these features could cause aerosol loss, we only evaluate the portion reaching the chamber by normalizing the infectious ratios.…”