Comparative Evaluation of Three Active Air Samplers for the Monitoring of Airborne Microorganisms

The evaluation of airborne microorganisms is critical in the biopharmaceutical industry. For manufacturers that produce drugs in an aseptic environment, cleanrooms must meet strict standards. Regulatory requirements such as the US Food and Drug Administration's Guidance for Industry, Sterile Drug Products Produced by Aseptic Processing: Current Good Manufacturing Practice and internal corporate policies require monitoring to verify that these standards are maintained. Cleanroom monitoring is dependent upon reliable instruments that are suitable for sampling airborne contaminants in an aseptic environment. These instruments must also be calibratable, portable, and easy to use

In this study, three active air samplers were evaluated for the collection of culturable airborne microorganisms. Bioaerosol collection includes whole microorganisms as well as fragments, toxins, and particulate waste products from all varieties of living things (1).

Table I: Estimates from the mixed-effects model of average recovery and standard deviation of the replicate measurements (within day) of the airborne culturable bacteria concentration by air sampler in log10(cfu/ft3) units.
Materials and methods Air samplers. The following air samplers were studied:
  • The "SAS Super 180" sampler (Bioscience International, Rockville, MD) aspirates air at 180 L/min through a solid 304 stainless steel sampling head with 219 precision-drilled holes positioned over the agar at a prescribed distance. After impaction, air exits through an exhaust screen. The unit can accommodate either a standard 55/84-mm contact plate or a 90-mm standard Petri dish below the sampling head. The sampler is fully programmable for features such as time between aspirations, volume of air for each aspiration, and total air volume to be sampled.
  • The "RCS Plus" (Biotest Diagnostics Corp., Denville, NJ) is a centrifugal impactor that draws air through the top of the instrument at 50 L/min. The air exits the unit through exhaust ports. The sampler is designed for unidirectional airflow that minimizes turbulence, thereby permitting sampling in laminar flow environments. The unit uses a proprietary air strip containing 34 wells each measuring ~1 cm2. The sample volume is programmable between 1 and 1000 L of air.
  • The "Air Ideal" sampler (Bio Merieux Inc., Hazelwood, MO) is an air sampler based on air impaction. The air is aspirated by a turbine at 100 L/min through a perforated surface. The holes form air jets that force the particles onto the agar placed underneath the grid. The unit can accommodate either a 90-mm standard Petri dish or a 65/70-mm contact dish. The sample unit is programmable for delay time and sample volumes.

Methods. When comparing various air samplers, the device properties of each piece of equipment must be taken into account (2). The three air samplers that were evaluated have various flow rates. Therefore, all instruments were run for the same period of time, not the same aspiration volumes. The same period of time was used to obtain each sample because of the varying population of airborne organisms from minute to minute. All sampling was conducted indoors in a nonclassified laboratory area of nonmicrobiological practices. The room's windows remained closed at least 24 h before measurements were taken. The opening of doors was minimal. Sampling times were chosen at random throughout the day and over a period of several days.

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