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Comparing The Growth DirectTM System Environmental Monitoring Cassettes vs. Conventional Media: Part II

Posted by Rapid Micro Biosystems on February 4, 2015

rapid_growthEfficient environmental monitoring (EM) is critical for pharmaceutical manufacturers in today's competitive, tightly regulated industry. While traditional methods for EM are effective and time-tested, however, they can't provide the speed and efficiency offered by automated rapid microbiological methods (RMM) such as the Growth DirectTM System.

In Part I of this series, we discussed the parameters of the study completed by Dawn McIver, President of MicroWorks, comparing a variety of attributes of both traditional contact plates and the Growth DirectTM Cassettes. We identified the incubation parameters chosen and the results of growth promotion:


In this installment, we'll address Ms. McIver’s results for airborne viable bioburden, naturally contaminated and inoculated surface contamination, as well as neutralization capability.

Airborne Viable Monitoring

The airborne viable monitoring test was conducted with a SAS air sampler fitted and calibrated to accommodate the Growth DirectTM System cassettes. SAS air samplers with Growth Direct Cassettes and conventional plates were placed in various locations to compare the performance with a variety of contamination levels. Overall, samplers were placed side by side at 20 different locations on three separate days for a total of 60 tests. Statistical analysis showed no significant differences between Growth Direct Cassettes and conventional plates.



Surface Bioburden Testing -- Naturally Contaminated and Inoculated

For the natural contamination test, a variety of surfaces were tested throughout an office, laboratory and warehouse, as well as the surfaces of the laminar flow hood and biosafety cabinets. The surfaces weren't treated or disinfected beforehand, and samples were collected in close proximity to each other. Statistical analysis of the data did indicate a difference between the plates and proprietary cassettes. However, Ms. McIver attributes this disparity to high variability on naturally contaminated surfaces.



For the tests of inoculated surfaces, Ms. McIver and her team studied the following areas common to manufacturing facilities:

  • Epoxy wall
  • Tile floor
  • Glass
  • Stainless Steel
  • Polyvinyl chloride (PVC piping)
  • Terrazzo flooring
  • HEPA curtain (plastic)
  • Conveyor belt

Challenge Organisms used for inoculation included a mold, a yeast, a spore and some environmental isolates. Four replicates of each surface were inoculated with each of the challenge organism. The target inoculum ranged from 25 to 100 CFUs per 0.1 mL. 128 samples were collected overall. Following are the results for inoculated glass, which is representative of the results for all other inoculated surfaces. The difference between the conventional plates and Growth Direct Cassettes was not statistically significant.



Neutralization Capability

Finally, Ms. McIver conducted a neutralization capability test of the Growth DirectTM System cassettes to verify their reliability in situations involving disinfectants. The disinfectants used were:

  • LpH – An acidic, phenolic cleaner and disinfectant
  • Vesphene – Alkaline phenolic cleaner and disinfectant
  • SporKlenz – Peracetic acid sterilant and disinfectant
  • TBQ – Ammonium-based alkaline cleaner and disinfectant
  • 70% IPA – Alcohol-based sanitizer

The neutralization tests included common surfaces such as epoxy wall, tile floor, glass and stainless steel. Shown below are the results for the epoxy wall.  The results demonstrated neutralization of common disinfectant had been achieved.


Concluding her study, Ms. McIver points out the results demonstrate that Growth Direct Cassettes are suitable for collecting surface and airborne samples in place of conventional contact plates. Visible colonies were easily counted, and they were also available for retention or further identification. This capability sets the Growth DirectTM System apart from other rapid methods, which often involve destructive techniques. The Growth DirectTM System automates and speeds up the time-tested compendial method, making it a top choice for microbiologists who need rapid results, with minimal resources and the ability to conduct targeted investigations immediately following an out-of-specification result.

Ms. McIver presented her results during an online seminar and the results of her study were recently published in the November/December Issue of American Pharmaceutical Review.  To learn more about the benefits of RMM technology, download our free guide to rapid, automated microbial detection and enumeration.

Compare Growth Direct EM Cassette to Conventional Media