Agar plate volume in bioaerosol impactors affects collection efficiency, but it is often overlooked in practice. This study investigated the effect of agar volume (20, 35, and 50 mL) and, consequently, jet-to-plate distance on accuracy of culturable impactors. Laboratory experiments investigated sensitive Escherichia coli and hardy Bacillus atrophaeus bacteria with a BioStage impactor. Outdoors bacterial and fungal sampling assessed effects of varying agar volume in BioStage, Samplair Lite, and SAS Super 180 multinozzle impactors relative to a reference BioStage with 35 mL agar. The results demonstrate that agar plate volume affects not only overall collection efficiency, but also species selection and colony masking. Culturable concentrations of E. coli in laboratory were underestimated by 35% when using 20 versus 35 mL agar volume (p < 0.001). However, data indicate selection of healthier bacteria, as E. coli colonies were significantly larger on 50 versus 20 mL agar plates (p < 0.001). For outdoors, lower agar volume significantly improved accuracy of Samplair relative to the reference BioStage for bacterial (p < 0.001) and fungal (p = 0.03) aerosols. Changes for other samplers were not statistically significant, likely due to wide variability in microbial profiles. Outdoors data indicate that culturable concentrations may be positively correlated with increasing dimensionless jet-to-plate distance, especially for bacteria (p = 0.04). This effect may be attributable to sampler jet dissipation with lower nozzle number impactors (i.e., the Samplair) being more sensitive. This study demonstrates that bioaerosol impactor agar plate volume should be considered prior to sampling.
All Science Journal Classification (ASJC) codes
- Environmental Chemistry
- Materials Science(all)