This test method is fully quantitative and it also avoids any loss of viable organisms through wash off. This makes it possible to produce statistically valid data using many fewer test and control carriers than other quantitative methods based on most probable numbers (MPN).

The design of the carriers makes it possible to place into each a precisely measured volume of the test suspension. The use of the threaded stir bars allows for efficient recovery of the inoculum even after its exposure for several hours to strong fixatives such as glutaraldehyde.

The membrane filtration step allows processing of the entire eluate from the test carriers and therefore the capture and subsequent detection of even low numbers of viable organisms that may be present.

This test can be performed with or without a soil load to determine the effect of such loading on microbicide performance. The soil load developed for this test is a mixture of three types of proteins (high molecular weight proteins, low molecular weight peptides, and mucous material) to represent the body secretions, excretions, or other extraneous substances that chemical microbicides may encounter under field conditions. It is suitable for working with the various test organisms included here. The components of the soil load are readily available and subject to much less variability than animal sera.

Since the quality of tap water varies considerably both geographically and temporally, this test method incorporates the use of water with a specified and documented level of hardness to prepare use-dilutions of test products. The U.S. Environmental Protection Agency’Scientific Advisory Panel (SAP) on Germicide Test Methodology has recommended the use of water with a standard hardness of 400 ppm as CaCO₃.

1.1 This test method is designed for use in product development and for the generation of product potency data. This test method permits the loading of each carrier with a known volume of the test organism. The incorporation of controls can also determine the initial load of colony forming units (CFU) of organisms on the test carriers and any loss in CFU after the mandatory drying of the inoculum.

1.2 This test method is designed to have survivors and also to be used with a performance standard. The surviving microorganisms on each test carrier are compared to the mean of no less than three control carriers to determine if the performance standard has been met. To allow proper statistical evaluation of results, the size of the test inoculum should be sufficiently large to take into account both the performance standard and the experimental variation in the results. For example, if an arbitrary performance standard of 6-log10 reduction in the viability titer of the test organism is used, and an inoculum size of 10⁷ CFU, then theoretically a maximum of ten survivors per carrier is permitted; however, because of experimental variability, the exact target may need to be higher than 10⁶ CFU/carrier, thus fewer survivors would be permitted.

1.3 This test method should be performed by persons with training in microbiology and in facilities designed and equipped for work with infectious agents at the appropriate biosafety level (3).

1.4 In this test method, SI units are used for all applications, except for distance, in which case inches are used and SI units follow.

1.5 It is the responsibility of the investigator to determine whether Good Laboratory Practice Regulations (GLPs) are required and to follow them where appropriate (40 CFR, Part 160 for EPA submissions and 21 CFR, Part 58 for FDA submissions).

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.