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The revised AOAC INTERNATIONAL Methods Committee Guidelines for Validation of Microbiological Methods for Food and Environmental Surfaces was approved by the Official Methods Board (OMB). The guidelines were reviewed by the Methods Committee on Microbiology and made available for stakeholder comments. The document provides guidelines for the AOAC validation of microbiological methods for food and environmental surfaces. It includes terms and their definitions associated with the Official Methods of AnalysisSM (OMA) and Performance Tested MethodsSM (PTM) programs and validation requirements for qualitative, quantitative, and confirmatory identification methods. The guidelines were developed by Sharon Brunelle (AOAC technical consultant), Robert LaBudde (Least Cost Formulations and AOAC statistical advisor), Maria Nelson (AOAC technical consultant), and Paul Wehling (General Mills/Medallion Laboratories and AOAC statistical advisor). AOAC developed revisions to the guidelines for validating microbiological methods in order to address ongoing statistical issues with unpaired sample study designs, to begin moving toward implementing the recommendations of the Presidential Task Force for Best Practices for Microbiological Methods (BPMM), and to harmonize many of the existing AOAC documents. Revisions include: (1) A broader scope, to include validation guidelines for PTM requirements; environmental surfaces; methods with multiple analytes; methods where no reference methods are available; and identification methods. (2) New terms and concepts for qualitative methods, which include probability of detection (POD), defined as the proportion of positive analytical outcomes for a qualitative method for a given matrix at a given bacterial level or concentration. It replaces the parameters of sensitivity and specificity. In addition, differential POD values and confidence intervals are used to compare candidate and reference methods rather than ratios or significance tests. Plotting POD values against analyte concentration allows for definition of the region of the limit of detection, a BPMM concept. (3) A more precise most probable number (MPN), by making use of the 20 replicate analyses performed for the reference method. An MPN calculator was developed by LaBudde to allow calculation of an MPN for variable numbers of replicates at each of three levels. The three levels used for the MPN calculation do not have to be 10-fold apart. The microbiology guidelines fall in line with many of the harmonization efforts. The revised guidelines incorporate the recommendations of the AOAC International Stakeholder Panel on Alternative Methods (ISPAM), with minor variations, for harmonization of microbiological and qualitative chemistry validation schemes. The revised AOAC INTERNATIONAL Methods Committee Guidelines for Validation of Microbiological Methods for Food and Environmental Surfaces will be available online at www.eoma.aoac.org. For more information, contact Deborah McKenzie, senior director, standards development, at dmckenzie@aoac.org.
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