Effect of Sampling Time and Sampling Media during Filter and Liquid-Impingement-based Sampling on Collected Bacterial Viability, Culturability, and DNA Concentrations

Sampling stress due to impingement and filtration on bioaerosols has been previously evaluated. However, how changes in sampling time, sampling media, and the refilling of liquid during impingement sampling affect the viability, culturability, and DNA concentrations of collected airborne bacteria remains largely unknown. This information is crucial for air sampling of pathogenic bacteria and subsequent analysis by molecular methods during microbial outbreak in communities. This study aimed to address these knowledge gaps by testing Escherichia coli collected over 15 to 120 minutes on filters of Button Samplers and in the liquid media of BioSamplers, with the collection liquid either replenished at 15-minute intervals or not replenished. The results indicate that changes in simulated sampling times, media, and the replenishment of media in impingement sampling can significantly influence the recovered quantity of viable and culturable bacteria, as well as DNA concentrations. It was found that using a BioSampler with Tween mixture (TM) solution replenishment can lead to a reaerosolization loss of 0.12% at a sampling time of 120 minutes. For filter-based sampling, the results show that both mixed cellulose ester (MCE) and polycarbonate (PC) filters imposed high stress on bacterial cells, leading to greater DNA losses. However, MCE filters were found to be more suitable for 120-minute sampling, as they achieved better bacterial viability and culturability, with a DNA loss percentage (DLP) of 61.16%. The DLP was found to be negatively correlated with viability (r = -0.762, p < 0.01) and culturability (r = -0.638, p < 0.01), respectively. This indicates that cell membrane damages occurred during filter- and liquid impingement-based sampling, resulting in significant DNA losses for microbial analysis. Comparing filter- and liquid impingement-based methods across different sampling times, the results suggest that a BioSampler with TM solution is preferable for sampling E. coli and similar environmentally sensitive pathogenic bacterial species. Additionally, the sampling time should be kept as short as reasonably possible to minimize stress on the collected bacteria.