Standard Test Method for Determining the Antimicrobial Activity of Immobilized Antimicrobial Agents Under Dynamic Contact Conditions
Immobilized, as chemically bonded, antimicrobial agents are not free to diffuse into their environment under normal conditions of use. Textile test methods, such as AATCC 147-2004, that are directly dependent on the ready leachability of the antimicrobial agent from the treated fabric are inappropriate for evaluating immobilized antimicrobial agents. This test method ensures good contact between the bacteria and the treated fiber, fabric, or other substrate, by constant agitation of the test specimen in a challenge suspension during the test period.
The metabolic state of the challenge species can directly affect measurements of the effectiveness of particular antimicrobial agents or concentrations of agents. The susceptibility of the species to particular biocides could be altered depending on its life stage (cycle). One-hour contact time in a buffer solution allows for metabolic stasis in the population. This test method standardizes both the growth conditions of the challenge species and substrate contact times to reduce the variability associated with growth phase of the microorganism.
Liquid analysis of antimicrobial activity of non-leaching agents provides the ability to completely wet-out a test substrate. With the use of wetting-agent surfactants, false negatives observed when comparing hydrophobic and hydrophilic substrates can be reduced.
This test method is not intended for directly comparing the activities of leaching and non-leaching antimicrobial agents. In liquid environments, leaching biocides may release the active ingredient at differential rates. Furthermore, residual antimicrobial activity of leaching biocides may be present in serial dilution and may exert additional activity after desired contact time, unless adequately sequestered at end of test. Controls for both of these factors are not included in this test method; therefore, screening protocols are introduced to identify the presence of leaching biocides.
The test is suitable for evaluating stressed or modified specimens, when accompanied by adequate controls.
Note 1—Stresses may include laundry, wear and abrasion, radiation and steam sterilization, UV exposure, solvent manipulation, temperature susceptibility, or similar physical or chemical manipulation.
1.1 This test method is designed to evaluate the resistance of non-leaching antimicrobial treated specimens to the growth of microbes under dynamic contact conditions. This dynamic shake flask test was developed for routine quality control and screening tests in order to overcome difficulties in using classical antimicrobial test methods to evaluate substrate-bound antimicrobials. These difficulties include ensuring contact of inoculum to treated surface (as in AATCC 100), flexibility of retrieval at different contact times, use of inappropriately applied static conditions (as in AATCC 147), sensitivity, and reproducibility. This test also allows for the versatility of testing contamination due to such things as hard water, proteins, blood, serum, various chemicals, and other contaminates or physical/chemical stresses or manipulations of the specimens of interest.
1.2 Surface antimicrobial activity is determined by comparing results from the test sample to simultaneously run controls.
1.3 The presence of a leaching antimicrobial is both pre- and post-determined by the presence of a zone of inhibition.
1.4 This test method should be performed only by those trained in microbiological techniques.
1.5 This standard may involve hazardous materials, operations, and equipment. 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.
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