Study finds plate choice can affect EM microbial air sampling accuracy and Annex 1 compliance

By Gill Power

Cherwell publishes study showing some current air sampling processes may fail to comply with new EU GMP Annex 1

Bicester, UK, 28th February 2023: Cherwell, specialists in cleanroom microbiology solutions for the pharmaceutical, healthcare and related industries, has published the findings of an investigative study  suggesting that prepared media plate choice can affect the accuracy of microbial air sampling. This is a significant finding as following the publication of the latest EU GMP Annex 1 revision, accuracy in air sampling and cleanroom monitoring has now become even more important for the manufacture of sterile medicinal products. Manufacturing organisations must be able to demonstrate that their environmental monitoring (EM) procedures meet the new more stringent standards.


Having been undertaking servicing and calibration of air sampling devices for over 35 years, Cherwell’s calibration engineering team had seen evidence that choice of plated prepared media can affect calibration results in some circumstances. This can in turn render any reading from a device inaccurate and non-compliant, therefore, Cherwell microbiologists undertook the study to investigate further and share results for wider discussion.

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The study tested the relative performance of plates from five leading prepared media suppliers using a standard set-up of an SAS air sampler calibrated to ISO 9001:2015 certification. The testing showed that results varied across different plate types, due to variations in size and form factor of the plates which can disrupt air flow through a sampler. This consequently causes over- or under-sampling in some cases, affecting results and data to potentially lead to inaccurate readings.


The study concludes that plate selection does make a difference, and that compliance with the latest revision of Annex 1, published in August 2022, will require organisations to ensure that their chosen plate, in combination with their chosen sampler, is giving an accurate result. Further recommendations include that air sampler calibration should be at least annual to reduce risk of incorrect sampling, and this calibration should include testing in conjunction with the prepared media plates routinely used by an organisation.


Hamish continued, “We undertook an impartial investigative study, so feel that our findings that plate choice can affect air sampling results accuracy is an issue that others should be aware of and would encourage them to conduct their own investigations. Only by working together and sharing knowledge can we advance this subject that is so important for Annex 1 compliance and the safe manufacture of sterile medicinal products.”


The report detailing the methods, results and recommendations of Cherwell’s study ‘Does plate choice change sampling accuracy?’ is available to download from Cherwell’s website at:




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