In another comparison test, microbial populations in cleanroom Class E (ISO 9), Class D (ISO 8, Class 100,000 at operational
and static), Class C (ISO 7/8, Class 10,000 at static and 100,000 at operational), and Class A (Class 100, ISO 5) environments
at the Bayer Berkeley Site were evaluated using the IMD-A, running it side-by-side with a conventional SAS air sampling method
(Bioscience International, Rockville, MD). SAS air sampling uses sieve impaction: air is aspirated for a specific time period
through a perforated cover plate. The air is then blown onto a solid agar media plate, where the particles are impacted. The
plates are incubated at an appropriate temperature and time period and the colony forming units (cfus) are counted. Environmental
air monitoring in the cleanrooms was performed over a period of eight weeks in areas where little or no manufacturing activities
were taking place. Because of the newer device's lower flow rate, for Class A, C, D, and E, 35 liters of air were sampled
using the IMD-A. For Class A, C, and D, 1,000 liters of air were sampled using the SAS air sampler. For Class E, 200 liters
of air were sampled using the SAS air sampler. Plates from the SAS air samplers were incubated for four days at 37 °C.
Microbial populations in environmental air in an unclassified office space environment were evaluated using the IMD-A and
AGI method coupled with ScanRDI analysis. One cubic foot of air was sampled with both the IMD-A and AGI. Then 100 mL of fluid
(Fluid A) from the AGI was membrane filtered and processed for ScanRDI analysis in accordance with the manufacturer's instructions.
We tested the samples in quadruplicate, with unused Fluid A serving as the negative control for the ScanRDI analysis.
REAL TIME RESULTS POSSIBLE WITH IMD-A
Figure 1A and Table 1 show summary results from the
1-m3 microbial barrier test chamber aerosol challenge study. In general, with the exception of one concentration range tested
(concentration 4), the mean biological counts from the IMD-A were equivalent or greater than the mean
spore counts recovered by the Anderson air sampler. Although at the lower concentration ranges (concentrations 1, 2, and
3) the microbial counts from both instruments were more or less the same, at the higher concentration range (concentration
5) the biological counts recovered by the IMD-A were substantially higher than those recovered by the Anderson air sampler.
Table 4. Statistical evaluation of 150-m3 microbial barrier test chamber data from the IMD-A, an Anderson air sampler, and AGI—linear fit of instrument correlation
Results from the
1-m3 microbial barrier test chamber aerosol challenge study are shown in Figure 1B and Table 2. At both concentrations tested,
the recovery of biological counts from the IMD-A were equivalent to or greater than the mean
vegetative cell counts recovered by the Anderson air sampler. The mean biological counts recovered by the IMD-A were 50%
and 25% higher than the microbial recoveries of
from the Anderson air sampler.