The standard “ASTM E2197-17 Standard quantitative disk carrier test method for determining bactericidal, virucidal, fungicidal, mycobactericidal, and spoicidal activities of chemicals” developed by the American Society for Testing and Materials (ASTM) describes a test method used to evaluate the ability to inactivate vegetative bacteria, viruses, fungi, mycobacteria, and bacterial spores on brushed stainless steel disk carriers representing hard, non-porous environmental surfaces and medical devices.
Also, this standard is designed to have survivors that can be compared with the average of at least three control carriers to determine whether the performance standard is met. For proper statistical evaluation of the results, the number of viable organisms in the test inoculum should be high enough to account for both the performance standard and experimental variations in the results. Also, this test method does not involve any wiping or scrubbing action. Therefore, it is not designed to test wiping operations.
For the purposes of this standard, the terms and definitions in the "ASTM E2756-19 Standard Terminology for Antimicrobial and Antiviral Agents" standard as well as the following definitions apply:
Each disk (1 cm in diameter) receives 10 µL of test organism with a soil load. The inoculum is dried and then the disk is placed on the inside bottom surface of a sterile plastic bottle before contact with 50 µL of the use dilution of the test substance. Contact time and temperature may be varied as required. Control carriers receive 50 µL of fluid that is innocuous to the test organisms and host cells if present, but are otherwise handled in the same manner as the test carriers.
For tests against vegetative bacteria, fungi, mycobacteria and bacterial spores, the test substance is then neutralized and the inoculum is eluted. The eluate and subsequent rinses of the carrier and its flask are passed through a membrane filter. Filtered culture plates are incubated, colonies are counted and log10 reductions are calculated.
For tests with viruses, appropriate dilutions of the eluate are inoculated into appropriate cell cultures, the cultures are examined for cytopathology/infectious foci, which most probable number estimated as foci or plaques and log10 is calculated.
The design of this test eliminates any loss of viable organisms through washing and thus makes it possible to produce statistically valid data using much less test carrier than required for methods based on simple most probable number estimates.
The rigor of the test is achieved by the use of a soil load, the micro-topography of the brushed stainless steel carrier surface, and the smaller ratio of test substance to surface area typical of many disinfectant applications. Thus, the test substance being evaluated faces reasonable difficulty in allowing efficient recovery of test organisms from inoculated carriers. The metal disks in the basic test are also compatible with a wide range of active substances.
The design of the carriers makes it possible to place a precisely measured volume of test organism (10 µL) and control fluid or test substance (50 µL) in each.
The inoculum is placed in the center of each disc, with volumes of test substance covering almost the entire disc surface, thus virtually eliminating the risk of exposure to any organism.
In all tests except those against viruses, the addition of 10 mL of eluent/diluent will allow the test substance to be diluted 1:200 immediately at the end of the contact time. Although this step alone is sufficient to stop the microbicidal activity of most actives, the test protocol allows for the addition of a specific neutralizer to the eluent/diluent if necessary. With the exception of viruses, the membrane filtration step also allows the entire eluate from the test carriers to be processed and therefore allows the capture and subsequent detection of even low numbers of viable organisms that may be present. Subsequent rinsing of the membrane filters with saline also reduces the risk of any inhibitor residues being carried over into the recovery medium.
Among the numerous testing, measurement, analysis and evaluation studies that our organization has provided for businesses in various sectors, our organization also provides testing services defined in the standard “ASTM E2197-17 Standard quantitative disk carrier test method to determine the bactericidal, virucidal, fungicidal, mycobactericidal and spoicidal activities of chemicals” with its trained and expert staff and advanced technological equipment.
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