ASTM International

Standard Guide for Evaluating Non-culture Microbiological Tests
 N E1326 REV A

Annotation

The purpose of this guide is to assist users and producers of non-culture microbiological tests in determining the applicability of the test for processing different types of samples and evaluating the accuracy of the results. Culture test procedures such as the Heterotrophic (Standard) Plate Count, the Most Probable Number (MPN) method and the Spread Plate Count are widely cited and accepted for the enumeration of microorganisms. However, these methods have their limitations, such as performance time. Moreover, any given culture test method typically recovers only a portion of the total viable microbes present in a sample. It is these limitations that have recently led to the marketing of a variety of non-culture procedures, test kits and instruments

Culture test methods estimate microbial population densities based on the ability of mircoorganisms in a sample to proliferate in or on a specified growth medium, under specified growth conditions. Non-culture test methods attempt to provide the same or complimentary information through the measurement of a different parameter. This guide is designed to assist investigators in assessing the accuracy and precision of non-culture methods intended for the determination of microbial population densities or activities.

It is recognized that the Heterotrophic Plate Count (HPC) does not recover all microorganisms present in a product or a system (1, 2).2 When this problem occurs during the characterization of a microbiological population, alternative standard enumeration procedures may be necessary, as in the case of sulfate-reducing bacteria. At other times, chemical methods that measure the rates of appearance of metabolic derivatives, the utilization of contaminated product components or genetic profile of the microbial population might be indicated. In evaluating non-culture tests, it is possible that the use of these alternative standard procedures might be the only means available for establishing correlation. In such cases, this guide can serve as a reference for those considerations.