AATCC 174-2011 (2016)e. Test Method for Antimicrobial Activity Assessment of New Carpets.
Test not accredited in our laboratory.
The AATCC 174 Standard describes the procedures for determination of the antimicrobial activity of new carpet materials. This standard consists of three test that can be used individually or in combination: a qualitative antibacterial evaluation (Test I), a quantitative antibacterial evaluation (Test II), and a qualitative antifungal evaluation (Trial III). These tests can also be used to evaluate the effect of a cleaning process on the antimicrobial resistance of carpets.
The Test I (Qualitative Assessment of Antibacterial Activity on Carpets: Single Streak Method) is a qualitative evaluation of antibacterial activity against grampositive and gramnegative bacteria using Staphylococcus aureus and Klebsiella pneumoniae as representative test organisms, respectively. In addition, other suitable species may be used depending on the intended end use of the test sample. For the test, 25 x 50 mm rectangular test specimens are used. If available, a piece of carpet of the same material, but without the antibacterial agent, can be tested, although this negative control is not essential for performance of the test. If it is desired to evaluate the durability of antibacterial activity, the specimens of carpet must be tested before and after cleaning according to the client´s instructions, including the number of cleaning cycles, that should indicate the client.
To perform the assay, specimens of test material, including the corresponding untreated controls of the same material (if available), are placed in intimate contact with the agar surface medium that has been previously inoculated with one of the test bacteria by making one long streak or line across the center of the plate. Each specimen is placed transversely across the inoculum streak, so that it covers the central part, but not the entire length of the streak. The procedure is repeated for each test microorganism. After incubation, the plates are examined, and it is determined: 1) the presence or absence of interruption of the bacterial growth along the inoculum streak below the test specimen and 2) the presence or absence of a clear zone of inhibition beyond the edges of the specimen. If a zone of inhibition exists, the width of the zone of inhibition around the test specimen must be determined. The standard does not indicate the criteria for passing the test, which must be agreed between the client and the interested parties. Nevertheless, the standard states that, to constitute acceptable antibacterial activity, there must be no bacterial colonies directly under the specimen in the contact area. If the durability of the antibacterial activity must be evaluated, the results of the specimens before and after the cleaning cycles should be evaluated.
The Test II (Quantitative Assessment of Antibacterial Activity on Carpets) provides a quantitative procedure for the comparison and evaluation of the degree of antibacterial activity against grampositive and gram-negative bacteria using Staphylococcus aureus and Klebsiella pneumoniae as representative test organisms. Other suitable species may also be used depending on the intended end use of the test sample. For this test, round specimens of the test carpet with a diameter of 48 mm are used and placed in glass jars. If available, specimens of carpet of the same material, but without the antibacterial agent, can be tested, although this negative control is not essential for performance of the test. In addition, uninoculated specimens of treated carpet can be used to determine the level of background organisms present in the carpet. If the durability of antibacterial activity must be evaluated, the carpet specimens should be tested before and after cleaning according to the client´s instructions, including the number of cleaning cycles.
In the assay, specimens are inoculated with a bacterial inoculum, onto carpet fibers pre-moistened in sterile deionized water. At zero contact time, the number of viable bacteria in each type of test specimens is determined. For this, neutralizer is added to each of the glass jars with the test specimens and the bacteria present in the samples are extracted by shaking and counted on agar plates. The rest of the test specimens are incubated during the time selected by the client (between 6 and 24 hours). Other periods can be tested if it is desired to evaluate the bactericidal activity of the treatment during said periods. After incubation, the microorganisms are extracted in neutralizer, and the number of viable bacteria present in each specimen is determined by plate counting. The percent reduction for each test specimen is calculated by comparing, in each type of specimen (treated, untreated, and specimens subjected to a certain number of cleaning cycles, if applicable), the number of viable bacteria recovered at zero time with the number recovered after the test time. The standard does not establish criteria for passing the test, which must be determined by the client and interested parties based on the intended use of the product.
The Test III (Antifungal Activity Assessment of Carpet Materials: Mildew and Rot Resistance of Carpet Materials) is performed to evaluate the antifungal activity of carpet and resistance to a common fungal organism on nutrient rich medium. To perform this test, round specimens of carpet with a diameter of 38 ± 1 mm are used. For primary backing assessment, an additional set of carpet specimens which have the face fibers removed to a height of 3 ± 1 mm may be included to place the fungal spore inoculum directly at the base of the fiber and evaluate the antifungal activity in the primary backing. If activity durability data is required, more carpet specimens should be tested before and after cleaning following the client directions. Each carpet specimen will be evaluated on both sides (the pile side and the backing of the carpet) in separate culture medium.
To perform the test, the surface of the agar medium plates is inoculated with a suspension of Aspergillus niger spores. Furthermore, the pre-moistened carpet specimens, are also inoculated with the Aspergillus niger spore suspension. Carpet specimens are inoculated on each of the two sides, in separate Petri dishes fiber side up and also fiber side down. If carpet specimens with shaven piles are being tested for the primary backing assessment, these pieces should also be inoculated on each of the two sides and placed on separate culture plates. After 7 or more days incubation of the inoculated plates with the test specimens, for each of the carpet specimens and each orientation (with the fibers facing up or down in the Petri dish), the size of any growth-free zone (in mm) produced by the face in contact with the agar is determined. Furthermore, the growth of fungi on the face of the carpet specimen located upwards, without contact with the agar medium, is recorded. The gradation of the fungal growth is stated according to the following scoring scheme: 0 = No growth, 1 = Microscopic growth (visible only under the microscope), 2 = Macroscopic growth (visible to the eye). If macroscopic growth is observed, growth is classified as: traces of growth (<10%), light growth (10-30%), medium growth (30-60%), heavy growth (60% to totally covered).
The specimens that the client must send for the test will depend on the requested test. To perform the Test I with Staphylococcus aureus and Klebsiella pneumoniae, 8 rectangular specimens of 25 x 50 mm of the antimicrobial treated carpet and 8 of the non-antimicrobial treated carpet (if available) should be provided. If the durability of the activity with cleaning must be evaluated, twice specimens, 16 of each type, must be sent, and the cleaning procedure that should be carried out in the laboratory must be indicated. To perform the Test II with Staphylococcus aureus and Klebsiella pneumoniae, 16 round of 48 mm diameter specimens of antimicrobial treated carpet and 20 non-antimicrobial treated carpet (if available) must be provided. If the durability of the activity with cleaning must be assessed, twice the number of specimens, 32 specimens with treatment and 40 without treatment, must be sent, and the cleaning procedure that should be carried out in the laboratory must be indicated. To perform the Test III with Aspergillus niger, 8 round specimens of 38 ± 1 mm diameter of the carpet with the antimicrobial must be sent. For primary backing assessment, additional 8 specimens with the fibers shaved to a height of 3 ± 1 mm must be provided. In addition, if the durability of the activity with cleaning must be assessed, twice the number of specimens, 16 specimens with treatment and 16 specimens with treatment with the shaven fibers, must be sent, and the cleaning procedure that should be carried out in the laboratory must be indicated.