Agar plates are essential tools in pharmaceutical environmental monitoring (EM).
Used as settle plates, they provide a reliable means of detecting microbial contamination in controlled environments, such as sterile drug production environments, particularly grade A cleanrooms, hospitals, and operating theatres, to ensure compliance with stringent industry standards.
As water evaporates, the physical integrity of the medium can be compromised
However, desiccation (loss of water from the media) can undermine their effectiveness, impacting microbial recovery and leading to false-negative results.
This article explores the causes of desiccation, its implications for Environmental Monitoring (EM), and practical strategies to mitigate this challenge.
Why is desiccation a problem?
Agar-based media are designed to provide optimal conditions for microbial growth, with sufficient water activity and nutrients. In EM, the primary function of settle plates is to support the growth of unwanted microorganisms that may be present in controlled environments. However, various factors can cause agar plates to dry out during the maximum recommended exposure time of four hours.
As water evaporates, the physical integrity of the medium can be compromised, affecting microbial recovery rates. As the agar shrinks, cracks may start to appear down the middle of the plate.
Low ambient humidity in cleanrooms, maintained at 30–40% relative humidity, further promotes agar desiccation
These cracks may allow contaminants to become trapped within the medium, making colony counting unreliable.
Desiccation can result in false negatives or underestimations of viable contamination levels. Given the strict regulatory requirements for pharmaceutical cleanrooms, any deviation from accurate environmental monitoring data could impact contamination control strategies and regulatory compliance.
What are the key causes of desiccation?
Understanding the root causes of agar desiccation is essential for identifying effective preventative measures.
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