How to choose between sedimentation and airborne bacterial sampling methods?

1. Regulatory Requirements
GMP requires that testing methods in the pharmaceutical industry refer to ISO testing standards. ISO 14698-1 on microbial contamination control regulations stipulates that microbial monitoring must evaluate collection efficiency. Sampling methods and equipment with high collection efficiency yield more representative data. For environments with low biological load, such as Grade A and B areas, active sampling methods like airborne microbial sampling should be prioritized over passive sampling methods like settle plate counting.
Guidelines for evaluating the collection efficiency of microbial samplers have been proposed. The current 2003 edition of ISO 14698 categorizes collection efficiency into physical collection efficiency and biological collection efficiency. Physical collection efficiency primarily focuses on whether the sampling method can effectively capture airborne microbial particles, while biological collection efficiency emphasizes whether the sampler or method can ensure the viability of these particles during collection.
 
II. Sampling Efficiency of Settled Microorganisms
The passive sampling method based on gravitational force yields a collection efficiency of 0.106 CFU/h for active particles with a particle size of 12 micrometers settling on a 9 cm sampling dish and 0.256 CFU/h for those settling on a 14 cm dish. For active particles with a particle size of 1 micrometer, the collection efficiency on a 9 cm dish is 0.008 CFU/h. If the maximum concentration limit for Class A zones is 1 CFU/m³, then a 9 cm dish would need to be exposed to the Class A zone for 1,250 hours (equivalent to 52 days) to detect a meaningful result (one CFU) in a low-biological-contamination environment.
Therefore, the "settle plate method" is "an extremely insensitive sampling approach," and "it better reflects the deposition effect of microbial particles, being more sensitive only when larger Petri dishes (e.g., 14cm) or multiple sampling dishes are used." The collection efficiency of active sampling methods for 1-micron particles is 2,250 times higher than that of the passive settle plate method with 9cm dishes. For microbial sampling in Grade A laminar airflow environments, more sensitive sampling methods are recommended.
For non-sterile processes with relatively high microbial loads in Grade C and D environments, sampling methods such as sedimented microorganisms can serve as a supplementary microbial sampling approach and be used in conjunction with airborne microorganism sampling methods. In Grade A and B environments, airborne microorganism sampling methods are more efficient and thus more suitable.

 

Conclusion
In summary, the validated airborne microorganism sampling method demonstrates higher collection efficiency compared to the sedimentation method, making it more suitable for critical, low-biological-load sterile production environments. The sedimentation method can serve as a supplementary approach for airborne microorganism sampling during production processes, applicable to less critical, high-biological-load non-sterile environments. However, improper placement or operational errors should be avoided to mitigate contamination risks. Regardless of the method employed, parameters such as location, sampling frequency, coverage duration, and flow rate should be determined based on a risk assessment of the production process.