Development of an Aerosol System for Uniformly Depositing Bacillus Anthracis Spore Particles on Surfaces

After the anthrax incidents in October 2001, several techniques used for sampling surfaces for biological agents were found to be inadequately validated, especially at low surface loadings. Therefore a test chamber was developed to produce sample sets having targeted surface concentrations of dry biological agent simulant. Dry spore aerosols were initially dispersed into the chamber at relatively high air concentrations, and monitored in real time. The concentration decay (due to stirred settling and dilution) was measured and when the targeted air concentration was reached, the sampling surfaces were uncovered and exposed to the settling particles until >99% of the particles had settled. Multiple agar plates were used to estimate the true colony-forming-unit (CFU) surface concentration. The uniformity of surface loadings was limited by random deposition of small numbers of particles on the surfaces (Poisson distribution) and was characterized by how much greater the observed variability was than that predicted by Poisson statistics. The flow-enhanced powder mixture appeared to affect the spores' ability to grow on the agar medium. Three ways of analyzing the agar plates were used to evaluate the effect of spore coatings on viability and to differentiate between number of spore-containing particles and the number of spores. The presence of spore agglomerates re-suspended by various sample handling activities in the chamber further increased the variability of deposited particles. Based on estimated airborne particle concentration, it was possible to predict mean agar plate concentrations within narrow confidence intervals (CI) at low (4.8 CFU, 95% CI 3.5–6.4), medium (20 CFU, 95% CI 17–23), and high (160 CFU, 95% CI 140–190) concentrations.

[1]  J. Brockmann,et al.  Evaluation of rayon swab surface sample collection method for Bacillus spores from nonporous surfaces , 2007, Journal of applied microbiology.

[2]  John E. Brockmann,et al.  Evaluation of a Wipe Surface Sample Method for Collection of Bacillus Spores from Nonporous Surfaces , 2006, Applied and Environmental Microbiology.

[3]  Jay R. Turner,et al.  Greased and oiled substrates as bounce-free impaction surfaces , 1987 .

[4]  David Leith,et al.  Method to evaluate the dustiness of pharmaceutical powders. , 2006, The Annals of occupational hygiene.

[5]  Alvin C.K. Lai,et al.  Modeling Indoor Particle Deposition from Turbulent Flow onto Smooth Surfaces , 2000 .

[6]  Douglas J. Beecher,et al.  Forensic Application of Microbiological Culture Analysis To Identify Mail Intentionally Contaminated with Bacillus anthracis Spores , 2006, Applied and Environmental Microbiology.

[7]  L. Stetzenbach,et al.  Monitoring airborne fungal spores in an experimental indoor environment to evaluate sampling methods and the effects of human activity on air sampling , 1993, Applied and environmental microbiology.

[8]  Tanja Popovic,et al.  Bacillus anthracis Aerosolization Associated with a Contaminated Mail Sorting Machine , 2002, Emerging infectious diseases.

[9]  J R Puleo,et al.  Wipe-rinse technique for quantitating microbial contamination on large surfaces , 1979, Applied and environmental microbiology.

[10]  Tracy L. Thatcher,et al.  Effects of room furnishings and air speed on particle deposition rates indoors , 2002 .

[11]  K. Willeke,et al.  Particle Reentrainment from Fibrous Filters , 1997 .

[12]  L. J. Rose,et al.  Evaluation of a Macrofoam Swab Protocol for the Recovery of Bacillus anthracis Spores from a Steel Surface , 2006, Applied and Environmental Microbiology.

[13]  Matthew S. Tezak,et al.  Evaluation of vacuum filter sock surface sample collection method for Bacillus spores from porous and non-porous surfaces. , 2007, Journal of environmental monitoring : JEM.

[14]  C. Weis,et al.  Secondary aerosolization of viable Bacillus anthracis spores in a contaminated US Senate Office. , 2002, JAMA.

[15]  M. Buttner.  Monitoring Airborne Fungal Spores in an Experimental Indoor Environment To Evaluate Sampling Methods and the Effects of Human Activity on Air Sampling , 1993, Applied and environmental microbiology.

[16]  Ruiguang Song,et al.  Guidelines for air sampling and analytical method development and evaluation (May 1995). Technical report , 1994 .

[17]  Paul Mead,et al.  Environmental Sampling for Spores of Bacillus anthracis , 2002, Emerging infectious diseases.

[18]  R E McCleery,et al.  Bacillus anthracis contamination and inhalational anthrax in a mail processing and distribution center , 2004, Journal of applied microbiology.

[19]  Antony J. H. Goddard,et al.  Stable tracer aerosol deposition measurements in a test chamber , 1995 .

[20]  Patricia Cruz,et al.  Evaluation of the Biological Sampling Kit (BiSKit) for Large-Area Surface Sampling , 2004, Applied and Environmental Microbiology.

[21]  Bette Jensen,et al.  Swab Materials and Bacillus anthracis Spore Recovery from Nonporous Surfaces , 2004, Emerging infectious diseases.

[22]  P. Baron,et al.  Bacterial endospore inactivation caused by outgassing of vapourous hydrogen peroxide from polymethyl methacrylate (Plexiglas®) , 2007, Letters in applied microbiology.

[23]  B. V. Bronk,et al.  Detection of Molecular Diversity in Bacillus atrophaeus by Amplified Fragment Length Polymorphism Analysis , 2004, Applied and Environmental Microbiology.