Microbial sampling criteria – particle measurement systems


In the pharmaceutical industry, ensuring sterility and minimizing microbial contamination are critical to maintaining product quality and safety. Microbial sampling is an important part of environmental monitoring, and understanding the optimal sampling criteria can significantly impact the effectiveness of sterility assurance programs.

Introduction to microbial sampling methods

In a pharmaceutical manufacturing facility, microbial sampling is performed using multiple methods, each with its own instruments and techniques. Primary methods include:

  • Surface sampling: Typically performed using swabs or contact plates to collect microbes from surfaces.
  • Passive environmental sampling of aerosols (air): Involves the use of settling plates to capture airborne particles that settle over time.
  • Active environmental sampling of aerosols (air): Uses devices that actively draw air through a collection medium, such as an impactor, to capture airborne microorganisms.

Features of sampling methods

Surface sampling

The efficiency of surface sampling depends on the method chosen – swabs or contact plates. For swabs, efficiency is affected by the motion used in sampling, whether small or large areas. Contact plates depend on factors such as pressure and contact time. Field validation of these methods is essential as different media and local environmental conditions (such as temperature and humidity) can influence the results.

Passive aerosol sampling

With passive sampling, settling plates are placed in the environment. Collection efficiency can be affected by local air currents and the possibility of media drying due to exposure. Proper placement and environmental conditions are critical for accurate results.

Active aerosol sampling

Active air sampling involves devices that actively suck air through a collection medium, often an agar plate. This method focuses on two main efficiencies:

  • Physical Collection Efficiency: Refers to the influence of microbes on the collection medium. Factors such as inlet velocity, flow rate, and the physical design of the sampler (such as the BioCapt® Adjustable Height Impactor) play a role in optimizing collection efficiency.
  • Biological Collection Efficiency: Includes the ability of the sampler to accurately capture and promote microbial growth.
Key factors affecting active air sampling:
  1. Effects: The speed at which air is drawn through the sampler affects the impact of microbes on the medium. The impact trajectory and slot width are critical to efficiency.
  2. Isokinetic sampling: To ensure accurate sampling without disturbing airflow patterns, the sampling probe must match the velocity of the incoming air (isokinetic condition). Deviations from this condition (superisokinetic or subisokinetic) can result in inaccurate sampling.
  3. Flow: The total flow rate through the sampler affects the speed and efficiency of sampling. High flow rates can cause the media to dry out more quickly.
  4. Drying out of media: High flow rates can accelerate drying of the medium, which can reduce the growth promotion of test isolates.

Physical d50 efficiency results:

The d50 value represents the particle size at which 50% of the particles are collected. This value is critical for understanding the efficiency of different samplers and their ability to capture different particle sizes.

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Manufacturing