N.61 – Choose and comparation of samplers

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Active Microbial Air Sampler idea

The portable active microbial air sampler collects a pre-determined volume of air that impacts against agar-based growth culture medium contained in a Petri dish or contact plate. The aspiration is produced by a motor-fan. The plate is then incubated at appropriate temperature and the number of colonies (Colony Forming Unit = CFU) per plate are typically reported to 1.000 litres of air.

Active Microbial Air Sampler Principle

The air is aspirated through small holes at the top of the air sampler according to the Anderson principle. The air impacts a Petri dish or a Contact plate containing the nutrient medium, forcing the bacteria and molds to stick to the surface of the agar. The speed of the impaction and the particle size efficiency is a function of the dimension of the holes of the aspirating head. The air flow typically aspirated is 100 or 200 litres per minute.

The air sampler features to consider

  • Light and portable instrument
  • User friendly instructions and easy to read and operate the command panel
  • Delay and remote activation function to reduce the possibility of human contamination
  • Accuracy of the flow rate in the range +/-2,5%
  • Possibility to use any type of Petri dishes or Contact plates from different producers in the same sampler
  • Any time Calibration monitor on line in a few minutes to avoid that the previous results before the official calibration are faulty and must be rejected
  • Possibility to have official yearly instrument calibration guaranteed in short time from the distributor / producer or in your premises
  • If it is necessary to growth bacteria and molds on different culture medium, the 2 or 3 aspirating head models are the correct solutions to save time and to reduce possible human contamination.
  • The 2 or 3 aspirating heads models are also ideal to collect samples at different times (e.g. at rest, in operation) to save operator time and to reduce possible human contamination.
  • The 2 or 3 aspirating heads model are also used to obtain a more average realistic microbial environmental situation because the microorganisms are not evenly distributed in the air.
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  • If compressed gas are to be monitored for sterility, the air sampler should have an appropriate device for this purpose.

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The air sampler comparison

The different air sampler comparison is directly performed in the typical room / place where the environment is monitored. it is sometimes requested a direct performances comparison between the old and the new systems.

  • It is suggested to establish a base line for total bacterial or mold counts obtained from the previous tests in the specific place. These results will be then compared to determine the performance similarity.
  • The new and the old system should running simultaneously at the same sampling point. The results are then compared.
  • It is important that the operator understand the correct use and application of both instruments.
  • The culture plates should be the same and with the correct volume of medium.
  • The air sampling volumes of the different samplers should be the same and the start / stop cycles should be at the same time.
  • The sampling point should be positioned in an area where there is not extreme variability during the test (e.g. hallways).
  • The air inlets of the two samplers should be oriented in the same direction and at the same level.

Conclusions

Each portable microbial air samplers has its own characteristics and it is not possible and, in any case, difficult guarantee the same results. What is more important is the consistency of the results and the trend of results.

Advises

The size of the microorganisms in the air and especially in clean room are predominantly between 3 and 15 microns.  Therefore the impaction active air samplers meets the requirements ISO 14698.