Surface Sampling of Spores in Dry-Deposition Aerosols

Abstract

The ability to reliably and reproducibly sample surfaces contaminated with a biological agent is a critical step in measuring the extent of contamination and determining if decontamination steps have been successful. The recovery operations following the 2001 attacks with Bacillus anthracis spores were complicated by the fact that no standard sample collection format or decontamination procedures were established. Recovery efficiencies traditionally have been calculated based upon biological agents which were applied to test surfaces in a liquid format and then allowed to dry prior to sampling tests, which may not be best suited for a real-world event with aerosolized biological agents. In order to ascertain if differences existed between air-dried liquid deposition and biological spores which were allowed to settle on a surface in a dried format, a study was undertaken to determine if differences existed in surface sampling recovery efficiencies for four representative surfaces. Studies were then undertaken to compare sampling efficiencies between liquid spore deposition and aerosolized spores which were allowed to gradually settle under gravity on four different test coupon types. Tests with both types of deposition compared efficiencies of four unique swabbing materials applied to four surfaces with various surface properties. Our studies demonstrate that recovery of liquid-deposited spores differs significantly from recovery of dry aerosol-deposited spores in most instances. Whether the recovery of liquid-deposited spores is overexaggerated or underrepresented with respect to that of aerosol-deposited spores depends upon the surface material being tested.Since 2001, the biological defense community has made great strides in improving our readiness to respond to and recover from an attack with a biological pathogen. Lessons learned in restoring operations within large building complexes contaminated with Bacillus anthracis spores or ricin toxin have led to the development of more-efficient tools for the detection of biological pathogens and means of decontaminating affected facilities. A key step in determining the extent of contamination during the initial stages of a bioterrorist attack and in ascertaining if a building can be reoccupied in the final stages of cleanup is our ability to effectively sample an area and deliver a specimen for testing.Currently there are several commercially available sampling products (2,3,8,9,16,23), but test data demonstrate that they are limited in their ability to detect and recover biological samples, with estimated recovery efficiencies ranging from approximately 10% to 40% (8,11,19). Studies have also shown that a significant proportion of the biological agent that can be sampled from a solid surface remains adhered to the sampling materials despite efforts to wash it off for testing or is lost during the sample processing (1,7,19).Historically, recovery efficiencies of swabs found in sampling kits have been calculated based on their ability to recover a liquid bacterial...

Development of an Aerosol Surface Inoculation Method for Bacillus Spores

“…A physical difference in the spore deposition patterns was observed to result from the two different methods. The spore deposition method developed in this study will help prepare spore coupons via aerosolization fast and reproducibly for bench top decontamination and detection studies.In response to the 2001 Bacillus anthracis spore incidents in the United States, many studies have investigated various technologies to sample media, detect biological agents, and decontaminate materials (3,9,10,(17)(18)(19)21). These laboratory studies typically use small coupons and laboratory inoculants to simulate the materials and biological agents that occur in field events.…”

Decontamination of Bioaerosols within Engineering Tolerances of Aircraft Materials

“…Several test chambers have been designed to aerosolize and then deposit biological simulants onto some type of coupon for further testing (Baron et al, 2007;Baron et al, 2008;Brown et al, 2007aBrown et al, , 2007bBrown et al, , 2007cButtner et al, 2004;Chen et al, 1999;Edmonds et al 2009;Estill et al, 2009;Kesavan, 2008;King et al, 2011;Farnsworth et al, 2006;;Feather and Chen, 234 2003; Byrne et al, 1995;Lai et al, 2002;Kenny et al, 1999;Koch et al, 1999;Lewandowski et al, 2010;Marple and Rubow, 1983;Park et al, 2009;Thatcher and Nazaroff, 1997). With few exceptions (King, 2010), these chambers were constructed to evaluate deposition or swipe sampling and have not been used to evaluate the effectiveness of decontamination methods.…”

“…The recovery operations from these attacks were complicated because there no sampling or decontamination standards existed (Edmonds et al, 2009). The CDC did provide guidelines for office personnel who might encounter a letter containing a suspicious powder.…”

“…Studies have been completed using five-20µL drops of 10 7 stock of BG spores, allowing the coupons to air dry a minimum of 3 hours or until all the liquid was completely evaporated (Edmonds et al, 2009). Ten-fold dilutions of the bacterial suspensions were completed with 100 μL of 165 suspension containing the specific species of bacteria under study which was spread onto trypticase TM soy nutrient agar in plastic Petri dishes (King et al, 2011).…”

Improved Recovery of Bacillus Spores from Nonporous Surfaces with Cotton Swabs over Foam, Nylon, or Polyester, and the Role of Hydrophilicity of Cotton in Governing the Recovery Efficiency

“…In addition, little information has appeared to be available from developing parts of the world with regard to effective spore surveillance, the input of which would become valuable in the event of an unprecedented public health hazard arising from the dreaded B. anthracis. Although different compositions of swabs, such as cotton, foam, polyester, rayon, sponge, and blends, are available commercially, none has been found to be universally acceptable (1,(3)(4)(5)(6). Cotton swabs are easily available worldwide and have registered higher RE than synthetic swabs in some studies (6).…”