Antifungal Performance Standards
Authored by: John Limbach, Microbac Laboratories, Inc.
The effects of fungal growth on building products, paper and textiles have been a major
concern of manufacturers for over 60 years. In recent years, the marketplace has been
inundated with fungal resistant coatings and products designed to inhibit fungal growth.
Several related industry organizations have developed testing standards for antifungal
performance testing.
Fungi grow in the form of multicellular filaments called hyphae. A connected network of
these tubular branching hyphae is referred to as a colony or a mycelium. They secrete
hydrolytic enzymes, mainly from the hyphal tips. These enzymes degrade complex
biopolymers such as starch, cellulose and lignin into simpler substances which can be
absorbed by the hyphae. In this way, fungi play a major role in causing decomposition of
organic material, enabling the recycling of nutrients throughout ecosystems. Fungi may
also degrade man-made polymer additives such as plasticizers, cellulosics, lubricants,
stabilizers and colorants contained in organic coatings and plastics and other building
products.
Fungi are grouped into four Phyla:
1: The Ascomycota Phylum contains 25,000 species, including Aspergillus,
Penicillium, Trichoderma, Aureobasidium and, Chaetomium. These fungi decompose
cellulose (wood, paper and paperboard), textiles, paint coatings, plastics, insulation and
leather, and are, therefore, employed in most of the ASTM Standard Test Methods.
These fungi which produce “fuzzy” mycelial colonies on organic matter are frequently
referred to as “Molds.”
The 1,500 species of yeasts belong to this phylum also. They are microscopic fungi
growing as single cells and do little damage to building products as their main source of
carbon is obtained from hexose sugars such as glucose and fructose, or disaccharides
such as sucrose and maltose.
2: The Basidiomycota Phylum contains 25,000 species of saprophytic mushrooms
which obtain nutrients from decaying organic matter.
3: The Zygomycota Phylum contains 600 species, including bread mold.
4: The Imperfect Fungi Phylum contains 25,000 species which do not fit into the other
Phyla and are grouped together for convenience. Many of these fungi are parasitic plant
pathogens.
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© 2011 Microbac Laboratories, Inc.
Antifungal Performance Standards
The following standards have been published for testing of materials for resistance to
fungi:
1: ASTM G 21 – Determining Resistance of Synthetic Polymeric Materials to Fungi.
2: ASTM C 1338 – Fungi Resistance of Insulation Materials and Facings.
3: ASTM D 2020 – Standard Test Methods for Mildew (Fungus) Resistance of Paper
and Paperboard.
4: ASTM D 5590 – Standard Test Method for Determining the Resistance of Paint Films
and Related Coatings to Fungal Defacement by Accelerated Four-Week Agar Plate
Assay.
5: ASTM D 3273 – Standard Test Method for Resistance to Growth of Mold on the
Surface of Interior Coatings in an Environmental Chamber.
6: ASTM E 154 – Resistance to Deterioration from Organisms and Substances in
Contacting Soil.
7: ASTM D 4300 – Standard Test Methods for Ability of Adhesives to Support or Resist
the Growth of Fungi.
8: ASTM D 4578 – Standard Method for Mold Growth Resistance of Blue Stock
(Leather).
9: MIL-STD 810G - Method 508.6. Determines whether fungus will grow on a device
exposed to warm, moist air in the presence of fungus spores?
10: TAPPI T 487 – Fungus Resistance of Paper and Paperboard.
11: AATCC 30 – Antifungal Activity, Assessment on Textile Materials: Mildew and
Rot Resistance of Textile Materials.
12: ISO 16869 – Assessment of the Effectiveness of Fungistatic Compounds in Plastics
Formulations.
13: ASTM D 6329 - Standard Guide for Developing Methodology for Evaluating the
Ability of Indoor Materials to Support Microbial Growth Using Static Environmental
Chambers.
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© 2011 Microbac Laboratories, Inc.
Antifungal Performance Standards
The ASTM G-21 and TAPPI T 487 procedures require a composite fungal spore
suspension to be sprayed upon the sample materials with an atomizer while the samples
are horizontal in a nutrient growth agar deficient in a carbohydrate source. Therefore, no
organic carbon nutrients are available. Photographic images are taken each week of the
four-week exposure. The fungal spores may grow on the sample only if they are capable
of extracting organic carbon from the sample.
The ASTM D 2020, ASTM D 4300, ASDM D 4578 and ASTM 5590 procedures call for
the specimen on a PDA (Potato Dextrose Agar) petri dish to be sprayed with a composite
of fungal spores. The specimens in the environmental chamber are thus surrounded with
heavy fungal growth in each petri dish for 28 days to test for antifungal activity and
leaching of the anti-fungal components into the PDA agar.
The ASTM D-3273 standard is for fungal growth in soil, contained in the humidified
environmental chamber. Air circulation within the environmental chamber circulates the
fungal spores in the chamber to the vertically suspended samples four inches over the
soil. Weekly photographic images of each sample are emailed to customers so they can
follow the progress of the testing.
The ASTM E-154 standard requires sample submersion in soil containing fungal spores
and bacteria. This three-month exposure inside the environmental chamber exposes
building materials to bacterial and mold attack. Each month, the weight of the samples is
checked to determine which samples are losing weight due to degradation by soil bacteria
and fungi.
The MIL-STD 810 involves spraying the test items with a composite of fungal spores and
supporting the test items in the environmental chamber for 28 days.
The test Standards call for specific fungi to be used for resistance testing. The ATCC
(American Type Culture Collection) identification numbers are provided in each test
method:
1. Aspergillus niger (ATCC 9642) is chosen from the 200 species of Aspergillus as this
species grows well on nutrient-depleted environments. Sixty species of Aspergillus are
encountered in human pathology. Aspergillus oryzae ferments rice starches to create
Japanese sake. Aspergillus niger is grown commercially to produce 99% of the global
citric acid. Aspergillus is grown in bioreactors to produce enzymes such as glucose
oxidase and lysozyme.
2. Penicillium pinophilum (ATCC 9644), formerly Penicillium funiculosum, is a fungus
that deteriorates plastics.
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© 2011 Microbac Laboratories, Inc.
Antifungal Performance Standards
3. Trichoderma virens (ATCC 9645), formerly Gliocladium virens, is chosen from the 32
species of Trichoderma as it is adapted to thrive in diverse situations and is a soil fungus
capable of inducing soft rot in wood. Other Trichoderma species produce industrial
enzymes such as cellulose, hemicellulase, xylanase and chitinase in bioreactors.
4. Trichoderma pseudotkoningii (ATCC 26801) is commonly found on wood and
degrades fungicides and chlorinated phenols.
5. Aureobasidium pullulans (ATCC 9348) is a staining soft rot fungus on wood products.
This fungus deteriorates plastics and paint and may present a problem in adhesive
degradation.
6. Chaetomium globosum (ATCC 6205) is commonly encountered in industrial spoilage
as it grows readily on paper and other cellulosics.
Microbac Laboratories, Inc. is prepared to analyze your antifungal performance
standards and assist you in developing products with superior fungal resistance. The
Venice (FL) Division of Microbac Laboratories maintains pure fungal cultures and
performs several of the accelerated ASTM, MIL-STD, TAPPI, AATCC and ISO
Standard Tests for fungal growth in humidity and temperature-controlled environmental
chambers. Antifungal performance validations are valuable to customers who develop,
sell, and use products which may be subject to attack by fungi.
For more information, please contact: microbac_info@microbac.com
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© 2011 Microbac Laboratories, Inc.