ISO 846:2019 pdf download – Plastics – Evaluation of the action of microorganisms
4.1 General
The test involves exposing test specimens of plastic to the action of selected test strains of fungi and bacteria (or, in the case of the soil-burial test, to microbially active soil) for specified or agreed periods of time under specified conditions of temperature and humidity. At the end of the exposure, the test specimens are assessed before and/or after cleaning by visual examination and/or any change in mass or other physical properties is determined. The results obtained with the specimens exposed to microorganisms (test series I) are compared with those obtained from retained reference specimens (test series 0) or sterile specimens (test series S) kept under the same conditions. In the case of testing fungistatic properties, a visual assessment is made between test specimens free of biocides and with those containing biocides to demonstrate the effect of a biocide in a qualitative manner. Short descriptions of the test methods used to determine the resistance of plastics to fungi (method A) or the fungistatic effects (method B), resistance to bacteria (method C) and resistance to soil microorganisms (method D) are given in 4.2 to 4.4.
4.2.1 Method A: Fungal-growth test
Test specimens are exposed to a mixed suspension of fungal spores in the presence of a humidity ≥95 % relative humidity. After the limited nutrients from the spore itself are depleted through formation of a germination tube, the fungi can only grow at the expense of the material of the test specimens. If the specimens contain no nutritive component, the fungi cannot develop mycelia and there will be no deterioration of the plastic. Method A is suitable for the assessment of the inherent resistance of plastics to fungal attack in the absence of other organic matter.
4.2.2 Method B: Determination of fungistatic effects
Test specimens are exposed to a mixed suspension of fungus spores in the presence of a complete nutrient medium, i.e. with a carbon source. Even if the plastic does not contain any nutritive elements, the fungi can grow over the specimens and their metabolic products can attack the material by metabolizing the nutrient-agar medium.
Any inhibition of growth either on the plastic or in the nutrient-agar medium (zone of inhibition) shows fungistatic activity of the plastic or the presence of a fungicidal treatment. In order to show a basic qualitative effect of a biocide in a plastic material, specimens free from biocide shall be included in the test. Only if these biocide-free specimens show more growth than the specimens containing biocides can a qualitative indication of fungistatic or fungicidal efficacy be determined.
4.3 Method C: Resistance to bacteria
The action of bacteria on test specimens is assessed using an incomplete medium without a carbon source 1) . If there is no growth in the agar surrounding the specimen, then the specimen does not contain any nutritive components. If a material to be tested claims added functionality, such as a product with hygienic effects, the plastic material should be tested according to ISO 22196 which provides guidance for measuring the basic antibacterial performance of non-porous (plastic) materials that have been treated with a biocide with the intention of introducing antibacterial/hygienic properties into that material.