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Materials under Fungal Attack

Because of their enzymatic activity diversity, fungi threaten the integrity of most commercial products. Any plant or animal derived material can serve as substrate for fungal growth as long as sufficient moisture is available. Unfortunately, even many artificial materials, such as plastic and glass, are subject to fungal attack. To prevent damage by fungi, many products are treated with fungicides. A series of tests have been devised to ascertain the growth promoting activity of materials to be used in the manufacture of various products. The basis for most of these tests is to challenge the material with test fungi and measure the growth of the organisms.

Spores from one fungus or a mixed culture of several selected fungi are inoculated onto sterile samples of the material and incubated. The choice of fungus depends on the product. For example, if the material is a new type of paint. The material is inoculated with spores an examined for growth over an extended time period, usually 28 days. Liquids can be inoculated directly; solid materials are usually placed in the surface of an agar lacking a carbon source or in a mineral salts solution. (The test material is the sole carbon source). Adequate moisture and oxygen must be available to support fungal growth. In fact, many tests are performed under very high humidity to stimulate tropical conditions. Fungi thrive in tropical environments and are notorious for their widespread destruction of manufactured products in such areas.
Another procedure is the soil burial test generally used for materials that will be in contact with the ground during use. Wood used in construction is subject to fungal attack unless treated with fungicides. Burial tests are performed on fungicide-treated wood as well as on untreated plastics under laboratory conditions or actual field conditions. Laboratory tests employ known fungal cultures in otherwise sterile soil. Buried materials are examined visually and tested for weight loss. If the material is serving as a substance for fungal growth, its weight should be reduced. Difficulties with this approach include the prolonged time periods needed to observe fungal growth and the difficulty in removing the mold and its spores from the sample prior to measuring weight loss.
The addition of preservatives to products is one way to prevent or slow fungal attack. Another way is to deprive them of moisture. Products that would otherwise be inhospitable to mold invasion may support mild growth if they are wet. Care when handling such products can keep them free of contamination and excess moisture.

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