Thursday, April 14, 2011

Validation using stressed organisms and statistics discussed at the PDA Annual Meeting

During the 2011 Annual PDA meeting in San Antonio, two sessions were dedicated to rapid methods. The first session focused on the advances and challenges for rapid methods. Sven Deutschmann (Roche Diagnostics) discussed the validation of the Rapid Micro Biosystems Growth Direct system for in-process control and water testing. As part of their validation strategy, they challenged the system with slow growing organisms and determined that a 33 hour incubation was suitable for the detection of microorganisms. Using eight different types of microorganisms, accuracy data between the rapid system and conventional plates was greater than 70%, and the precision of the RMM was within the expected acceptance criteria as recommended in USP 1223. Next, they used stressed organisms to challenge the system in a similar fashion. Three organisms were chosen and they incubated these at 60 degrees C until the viability of each was reduced by 50% as compared with untreated organisms. These stressed organisms were also shown to be detected in the RMM within 33 hours. A separate set of experiments were conducted with pH-stressed organisms. They exposed the organisms to a pH 3 environment and determined the exposure time that gave at least a 90% reduction in viability was sufficient to generate stressed organisms for the same studies. These organisms were then tested as previously described and it was also determined that a 33 hour incubation would detect these stressed organisms as well.

Julie Schwedock (Rapid Micro Biosystems) then discussed the use of statistics that have been recommended in the USP, Ph. Eur., and PDA TR33. She provided a very understandable review of current expectations when using statistics as well as their limitations, and offered alternative statistical models for use depending on the expected bacterial population and the validation criteria that was being evaluated. A discussion of the use of the T test and the F test was provided, and actual data was presented that demonstrated the current compendial methods may not actually meet the statistical requirements of the compendia themselves! This was a very informative presentation and the audience applauded Julie's ability to discuss statistics in a manner that was understandable by all who attended.


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