The effect of filter material on bioaerosol collection of Bacillus subtilis spores used as a Bacillus anthracis simulant

Abstract

The objective of this study was to determine filter materials and extraction methods that are appropriate to use for environmental sampling of B. anthracis. Four types of filters were tested: mixed cellulose ester (MCE) with a pore size of 3 μm, polytetrafluoroethylene (PTFE) with pore sizes of 1 and 3 μm, and gelatin with a pore size of 3 μm. Bacillus subtilis var. niger endospores (also known as Bacillus globigii [BG]) were used as a surrogate for B. anthracis. Endospores were collected into Button Inhalable Aerosol Samplers with sampling times of 15 minutes, 1 hour, and 4 hours. Physical collection efficiency was determined by measuring upstream and downstream B. subtilis concentrations with an optical particle counter. Vortexing with ultrasonic agitation and vortexing with shaker agitation extraction methods were evaluated. The MCE, 1 μm PTFE, and gelatin filters provided physical collection efficiencies of 94% or greater. The 3 μm PTFE filter showed inconsistent physical efficiency characteristics between filters. Epifluorescence microscopic analysis of the gelatin filter extraction fluid revealed the presence of contamination by non-culturable bacteria. Mean differences for microbial culturability were not statistically significant for filter materials and extraction methods. However, the vortexing with shaker agitation extraction method resulted in higher total microbial counts in the extraction fluids for MCE and 1 μm PTFE filters when compared to vortexing with ultrasonic agitation. In summary, the MCE and 1 μm PTFE filters in combination with vortexing and shaker extraction demonstrated the best performance for the filter collection and extraction of BG spores.