In the 1-m3 barrier test chamber, bacteria were disseminated using a Chicago nebulizer. We performed experiments at five different spore
concentrations, with tests repeated at least three times at each concentration. Microbial measurements of the environmental
air in the barrier test chamber were done using the IMD-A (BioVigilant Systems, Inc., Tucson, AZ) and the Anderson air sampler
(Anderson Instrument Company, Fultonville, NY), a conventional device that relies on an impaction method to enumerate microorganisms
in environmental air. SCDA plates from the Anderson air sampler were incubated for four days at 37 °C. In a second study,
vegetative cells of Staphylococcus aureus were used. Culture preparation was similar to that described above for B. atropheus except that no heat shock treatment was performed. Experimental set-up was similar to that described above for B. atropheus, except that vegetative cells of S. aureus were tested at two different concentrations and the tests were repeated at least five times at each concentration. For both
studies, data were normalized to account for the different flow rate between the Anderson air sampler and the IMD-A.
Table 3. Statistical evaluation of 150-m3 microbial barrier test chamber data from the IMD-A, an Anderson air sampler, and AGI—Bacillus atropheus (spores)
The 150-m3 microbial barrier test chamber aerosol challenge study was performed at the US Army's Dugway Proving Ground (Dugway, UT).
In this study, B. atropheus spores were prepared similarly to the method described above for the 1-m3 microbial barrier test chamber challenge study. B. atropheus spores were disseminated in the 150-m3 barrier test chamber using a proprietary ultrasonic methodology that can specify the size and likely number of bacteria per
aggregate to a high degree of accuracy. Nominal concentrations of B. atropheus spores were dispersed over four runs: 30 cfu/L at 1.0 µm, 30 cfu/L at 2.5 µm, 300 cfu/L at 1.0 µm, and 300 cfu/L at 2.5 µm.
Microbial measurements of the environmental air in the barrier test chamber were performed using the Anderson air sampler
and using two IMD-A instruments, each placed at opposite ends of the chamber, and an all glass impinger (AGI), a glass bubble
tube used to sample air. In the AGI method, a known volume of air is actively pumped through an impinger containing a liquid
medium. SCDA plates from the Anderson air sampler were incubated for four days at 37 °C. To assess the AGI, liquid obtained
was filtered onto a membrane to capture cells and the membrane was placed on a media plate and incubated to evaluate microbial
growth. The membrane filters were transferred to SCDA media plates and incubated for four days at 37 °C. The results obtained
from the Anderson air sampler, AGI, and the two IMD-A units were normalized to account for different flow rates in the three
types of instruments.