Testing Services

Microbiological Analysis

Fungal Resistance

Microbac Laboratories, Inc. is prepared to analyze your antifungal performance standards and assist you in developing products with superior fungal resistance. Microbac 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.

Fungi are grouped into four Phyla:
 

1: The Ascomycota Phylum contains approximately 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 approximately 1,500 species of yeasts also belong to this phylum. 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 approximately 25,000 species of saprophytic mushrooms which obtain nutrients from decaying organic matter.

3: The Zygomycota Phylum contains approximately 600 species, including bread mold.

4: The Imperfect Fungi Phylum contains approximately 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.

The following standards have been published for testing of materials for resistance to fungi:
 

• ASTM G 21 – Determining Resistance of Synthetic Polymeric Materials to Fungi

• TAPPI T 487 – Fungus Resistance of Paper and Paperboard

ASTM G 21 & 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.

• ASTM D 2020 – Standard Test Methods for Mildew (Fungus) Resistance of Paper and Paperboard

• ASTM D 4300 – Standard Test Methods for Ability of Adhesives to Support or Resist the Growth of Fungi

• ASTM D 4578 – Standard Method for Mold Growth Resistance of Blue Stock (Leather)

• 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

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.

• ASTM D 3273 – Standard Test Method for Resistance to Growth of Mold on the Surface of Interior Coatings in an Environmental Chamber - This 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.

• ASTM E 154 – Resistance to Deterioration from Organisms and Substances in Contacting Soil - This 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.

• MIL-STD 810E - Method 508.4 - Determines whether fungus will grow on a device exposed to warm, moist air in the presence of fungus spores. 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.

• ASTM C 1338 – Fungi Resistance of Insulation Materials and Facings

• AATCC 30 – Antifungal Activity, Assessment on Textile Materials: Mildew and Rot Resistance of Textile Materials

• ISO 16869 – Assessment of the Effectiveness of Fungistatic Compounds in Plastics Formulations

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.

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.