The ability of an instantaneous microbial detection system (IMD-A) to monitor microbial populations in environmental air was
evaluated. The IMD-A results were compared with results from conventional environmental air monitoring methods. The comparisons
were carried out in controlled microbial barrier test chambers and in cleanroom environments. Additionally, microbial populations
in environmental air in an unclassified environment were evaluated using the IMD-A and the all-gas impingement (AGI) method
coupled with ScanRDI. In 1-m3 and 150-m3 controlled-barrier test chamber studies the mean recoveries with the IMD-A were equal to or greater than the mean recoveries
obtained with the Anderson air sampler at various concentrations. The mean microbial recoveries obtained using the AGI were
higher, but in the same order of magnitude, as those recovered by IMD-A. In classified environments, microbial recoveries
from the SAS air sampler were substantially lower than microbial counts detected by the IMD-A. There were reasonable correlations
of microbial recoveries between the IMD-A and the SAS air sampler results in cleanroom environments. Mean microbial recoveries
from environmental air in an unclassified environment were similar in the IMD-A and AGI methods coupled with ScanRDI analysis.
These results suggest that the IMD-A has the potential to reliably and instantaneously evaluate microbial populations in environmental
air to provide a valuable technique for biopharmaceutical manufacturing.
ENVIRONMENTAL MONITORING METHODS
Examining the microbial content of air is a key component of environmental monitoring in pharmaceutical cleanroom environments.
Overall environmental air monitoring also includes evaluating the particulate content of the air. Typically, particulate content
at 5.0 and 0.5 Ám levels is measured using total particulate monitoring systems such as the Climet, PMS, Royco, Lighthouse,
APC units, or similar systems.
Evaluating microbial content in environmental air involves both active and passive air monitoring. Active microbial content
in environmental air is typically evaluated using SAS, MAS, RCS, Mattson Garvin, Anderson air, liquid impinger, or SMA air
sampling systems. Active air monitoring often involves the use of a device in which microorganisms from a known volume of
air are captured on media plates, or alternatively, air is aspirated into a liquid and the microorganisms in the liquid are
captured on a membrane filter and transferred to media plates to evaluate growth. Viable passive air is evaluated by the plate-count
method using settling plates. Results from the microbial monitoring of the environmental air are typically not obtained until
3–5 days after sampling.
That need to wait for several days to accommodate microbial growth before acquiring monitoring data has been a major limitation
of conventional environmental monitoring methods. Over the past decade, several rapid culture- and nonculture-based methods
have been developed to provide much faster turnaround for microbial data.1
Table 1. Statistical evaluation of 1-m3 microbial barrier test chamber data from the IMD-A and an Anderson air sampler—Bacillus atropheus (spores)
One promising nonculture-based rapid method receiving increased attention in recent years involves the ScanRDI system (Chemunex,
France).2 In this semiautomated system, the total number of viable organisms is determined by filtering samples through a membrane
and labeling cells using a nonfluorescent substrate that diffuses across the cell membrane. This labeling differentiates between
viable and dead cells based on the presence or absence of esterase activity and intact cell membranes. Only viable cells with
membrane activity are able to cleave the dye and retain the fluorescent label. These viable microbial cells are quantified
by scanning and counting using laser cytometry. Although the ScanRDI system offers the advantage of rapid evaluation of microbial
populations, it is fairly specialized and does not allow for real-time detection of microbial populations. An ideal system
for microbial air monitoring in pharmaceutical cleanroom environments would require little or no sample preparation or manipulation
and would provide environmental microbial air monitoring data in real time.