The Most Probable Number (MPN) Method – Let’s Expand our Toolbox in the QC Microbiology Lab

Webinar to be presented Thursday, May 31 at 2 pm EST


The “Most Probable Number” (MPN) Method is a useful, if underutilized, tool for the microbiologist. It is part of the harmonized compendial chapter on bacterial enumeration and has been part of the Microbial Limits Test chapter in USP since the chapters inception in USP XVIII (1970). The test is a method to estimate the concentration of viable microorganisms in a sample by means of replicate liquid broth growth in ten-fold dilutions. It is particularly useful with samples that contain particulate material that interferes with plate count enumeration methods.  The method offers real opportunities as a tool for microbiologists in situations where, for one reason or another, the plate count method is unsuitable. It can also be employed for semi-quantitative estimation of growth-promotion capability of liquid media, in estimation of precision for alternate microbiological methods, and as part of the “fraction negative” method of determining D-values.

This webinar will review the MPN method and provide several suggestions of ways to use this method to expand the range of control that the QC lab can enjoy on media, microorganisms and on qualification of alternate (rapid) microbiological methods (RMM).

Register Here!

Scott Sutton, Ph. D.

Dr. Scott Sutton earned his Masters and PhD in Microbiology from the University of Rochester (NY). With over 20 years of laboratory leadership experience in the microbiology arena of the pharmaceutical and personal products industries, he now consults through Microbiology Network, Inc. Clients have included startups, generics, established Fortune 500 companies, law firms and investment broker houses. Laboratory management, training, GMP, testing methodologies and microbiology-related project management are areas of special interest. He has worked with the USP Microbiology Committee of Experts since 1993, serving as vice-chair since 2000. He operates the Pharmaceutical Microbiology Forum with its monthly newsletter ( and serves as a reviewer for several peer-reviewed journals. Dr. Sutton also operates an information source on the internet – The Microbiology Network ( that provides services to microbiology related user’s groups. This service also supports three Email lists, the first devoted to pharmaceutical microbiology, the second devoted to pharmaceutical stability and the third to cleanrooms and controlled environments.

Key Topics

  • The MPN (Most Probable Number) method
  • Use in compendial Tests
  • Utility beyond standard tests
    • D-value
    • Trending environmental monitoring data
    • Qualification of alternate microbiological methods
    • Growth Promotion Testing
    • Qualification of alternate microbiological methods