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1.1 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.

1.2 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.

1.3 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.

1.4 Because there are so many types of tests that could be considered non-culture based, it is impossible to recommend a specific test protocol with statistical analyses for evaluating the tests. Instead, this guide should assist in determining what types of tests should be considered to verify the utility and identify the limitations of the nonconventional test.

1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

5.1 This guide should be used by producers and potential producers of non-culture tests to determine the accuracy, selectivity, specificity, and precision of the tests, as defined in Practice E691. Results of such studies should identify the limitations and indicate the utility or applicability of the non-culture test, or both, for use on different types of samples. Guide E1488 recommends other statistical tools for evaluating the suitability and applicability of proposed new test methods.

5.2 Non-culture test users and potential users should employ this guide to evaluate results of the non-culture test as compared to their present methods. Practices D5245 and D5465 should be reviewed in regards to the microbiological methods employed. If culture methods have not been used for monitoring the systems, then guidelines are included for obtaining microbiological expertise.

5.3 Utilization of a non-culture test can reduce the time required to determine the microbiological status of the system and detect microbe that are not detected by culture testing. Consequently, non-culture tests can contribute to the improvement in the overall operating efficiency of microbial contamination condition monitoring and diagnostic efforts, and microbicide performance evaluations.

5.4 Detecting microbial contamination levels that exceed predetermined upper control limits indicates the need for an addition of an antimicrobial agent or other corrective maintenance action. By accurately determining this in a shorter time period than is possible than by culture methods, treatment with antimicrobial agents may circumvent more serious problems than if the treatment were postponed until culture results were available. If the antimicrobial treatment program relied on an inaccurate non-culture test, then unnecessary loss of product and problems associated with inappropriate selection or improper dosing with antimicrobial agents would exist.

5.5 Since many methods based on entirely different chemical and microbiological principles are considered, it is not possible to establish a unique design and recommend a specific method of statistical analyses for the comparisons to be made. It is only possible to present guides that should be followed while performing the experiments. It is also recommended that a statistician be involved in the study.