Factors affecting the recovery of microorganisms from surfaces using contact plates in cleanrooms.

13:53 - 04/09/2025 105

Investigate factors affecting the efficiency of microbial recovery from cleanroom surfaces: roughness, material type, contact time and compare with the swab method.

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☰ Table of Contents

1. The Importance of the Contact Plate Method in Microbial Monitoring
2. Surface Materials and Microbial Recovery Efficiency
3. Contact Time and Pressure on the Contact Plate
4. Microbial Recovery by Material Type and Practical Applications
5. Comparison Between Contact Plate and Other Methods
6. Conclusion & Recommendations

The Importance of the Contact Plate Method in Microbial Monitoring

The contact plate method is the standard used to check microbial contamination on surfaces in cleanrooms, especially when producing sterile products according to Annex 1 – EU GMP. This device is useful for monitoring equipment, protective clothing, and surfaces close to the product.

Surface Materials and Microbial Recovery Efficiency

A study from AstraZeneca Group indicated that surface roughness is an important factor affecting microbial recovery performance:

Copolyester protective glasses (roughness ~0.153 µm) and stainless steel (about 0.496 µm) have high recovery efficiency (~80%).
Polyester cleanroom clothing (roughness ~10.973 µm) is less effective, due to its rough surface retaining microorganisms.

The smoother the surface, the harder it is for microbial particles to hide and the easier they are recovered into the agar environment.

Contact Time and Pressure on the Contact Plate

Another study on stainless steel and vinyl surfaces showed:

When the contact plate is pressed for 20 seconds with even pressure, the recovery efficiency is better than for 10 seconds.
Extending contact time to 30 seconds does not significantly improve recovery results.

Microbial Recovery by Material Type and Practical Applications

In practical tests with 5 common materials in cleanrooms (polyester clothing, latex gloves, EPDM gloves, copolyester glasses, and steel trays), the microbial recovery rates vary:

Polyester, latex, EPDM have about 70% efficiency.
Copolyester glasses and steel trays reach ~80%.

This reflects the reality that microorganisms vary in size and nature, affecting their adhesion and distribution on different materials.

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Comparison Between Contact Plate and Other Methods

Contact plates usually yield better microbial recovery results compared to swabs when testing flat, smooth surfaces.
For uneven surfaces or complex structures, swabs are a more suitable choice.

Conclusion by Anh Khang

Factor	Impact on Microbial Recovery Efficiency
Smooth surfaces (steel, glass)	High efficiency (~80%)
Rough surfaces (polyester)	Lower efficiency (~70%)
Contact time	20 seconds is optimal
Contact plate vs Swab	Contact plate superior on flat surfaces

Recommendations:

Understand surface characteristics to choose the appropriate sampling method.
Standardize contact time and pressure to ensure consistency.
Combine contact plates with swabs when testing complex surfaces to optimize results.

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