Verifying accurate environmental monitoring of viable particles

Routine testing ensures standards are being met

By Fran McAteer, Microbiology Research Associates, Inc.

This article presents a testing methodology for environmental monitoring (EM) of viable particles in a cleanroom. Viable particles are living microscopic organisms present in the aseptic environment, especially bacteria, yeast, and mold in the air and on surfaces. Thorough testing usually includes monitoring surfaces, personnel and air. Companies routinely test their cleanroom environments to ensure they meet required standards. Cleanroom operating standards are found in United States Pharmacopeia (USP) and European Pharmacopeia (EP), and International Standards Organization (ISO).

Viable sampling of air

For sampling, gravitational or settling plates are used. These are Petri dishes containing sterile growth media. They are passively exposed to the environment, usually for 30 to 60 minutes. Viable microorganisms that settle onto the media surface grow when the plates are incubated. Though settling plates offer ease of use and remain cost effective, they do not directly correlate microbial contamination with measured air volume and do not provide a quantitative measurement of air contamination.

Another approach is the use of rotary centrifugal air samplers (RCS). These active monitoring instruments measure an exact amount of air with a quantifiable number of viable microorganisms. Contamination can be measured per cubic foot or cubic meter of air (see Fig.1).

Viable sampling of surfaces

Contact or Rodac plates are also Petri dishes containing sterile growth medium. In this case, the agar protrudes above the sides of the plate. The convex contact plate is pressed against any flat, regular surface that needs to be sampled. Any viable microorganisms on that surface will adhere to the agar and grow upon proper incubation. This technique replicates the number of viable microorganisms on a surface. Contact plates are easy to use and widely available, but may not be appropriate for irregular surfaces.

Figure 1. Rotary centrifugal air samplers (RCS) are active monitoring instruments that measure an exact amount of air with a quantifiable number of viable microorganisms. Photo courtesy of Biotest Diagnostics.
Click here to enlarge image

Swabs are used for sampling of uneven surfaces, such as tubing or equipment. Swabbing is qualitative and is technique-dependent. A 2 in2 x 2 in2 sample site is swabbed by using a back and forth technique and rotating 90° and repeating. The swabs are then streaked onto microbiological agar plates for identification.

Figure 2. Swabs are used for sampling of uneven surfaces, such as tubing or equipment. Photo courtesy of ITW Texwipe.
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Viable monitoring of personnel
Personnel working in a cleanroom also need to be monitored for microbial contamination. Personnel monitoring is an indication of gowning proficiency. Sampling sites are located on both gloves and gowns. Touch plates (contact plates) can be used to dynamically monitor technician’s hands immediately after a critical process.


Sampling locations are selected based on many factors including potential product exposure areas, processing parameters, equipment design, and validation data. Frequency of monitoring depends on product and quality requirements, and sampling frequency changes should be based on trending analysis and changes in equipment, processing or personnel. A sampling plan describing procedures and identifying sample sites, sampling numbers, and sample frequency should be developed at every regulated company. Testing should be performed during static and dynamic situations.

Action/alert levels

Based on environmental monitoring data, companies must establish action levels, which describe the level of microbial contamination that triggers a planned sequence of corrective actions. The purpose of corrective actions is to return a facility to acceptable limits of viable microorganisms as quickly as possible. These actions will include a determination of what caused the viable counts to be above acceptable limits and how that will be rectified in the future. Exceeding the alert level should cause the company to increase sampling intensity or frequency in the affected area.


Overall, the EM program provides proactive feedback to the cleanliness of a manufacturing operation. It is a proven, effective measurement of quality levels for companies in regulated industries.


1. U.S. Pharmacopeia Convention, Inc. United States Pharmacopeia and National Formulary (USP-NF), 29th edition, Rockville, MD. (2004).

Fran McAteer is vice president of quality at Microbiology Research Associates, Inc. (Acton, MA), an FDA-registered contract microbiology testing laboratory specializing in USP testing for pharmaceuticals, biologics, and medical devices. He has expertise and experience in EM programs and acts as a consultant for many companies. He can be reached via e-mail at [email protected]


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