AOAC Germicidal Spray Test Modified for Fungi

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Below, you will find a summary of the AOAC Germicidal Spray Products Test method, modified for use with fungi. The method is sometimes modified for use with fungi to support supplemental efficacy (fungicidal) label claims for pesticides registered with the United States Environmental Protection Agency. Trichophyton mentagtrophytes is the preferred test microorganism for substantiation of fungicidal efficacy claims, but the lab can perform the test using any microorganism from our microbial library.

Please note that some fungi require long periods of time to grow and sporulate and that influences the amount of time required for the laboratory to perform the test.

Summary of the Germicidal Spray Test Method Modified for Fungi
  • Yeast or Mold can be tested using the Germicidal Spray Test modified for fungi.
  • Fungi are cultured, harvested, and supplemented with serum if requested to simulate an organic soil load.
  • A 0.010 ml volume of the fungal suspension is spread evenly over the surface of a number of glass test carriers and dried, thus creating a film of fungi.
  • The dry, contaminated test surfaces are placed in Petri dishes and then sprayed, individually, with test product in accordance with manufacturer instructions.
  • Depending on the purpose of the test, either 10 or 60 contaminated test surfaces may be treated with the disinfectant product.
  • Contaminated test surfaces are covered with the fungicide (which normally pools, covering the entire surface of the slide) for a contact time specified by the study sponsor.
  • Once the contact time has concluded, the treated test surfaces are aseptically transferred, individually and at intervals to sterile test tubes containing a liquid growth medium that has been amended with chemical agents to immediately neutralize the action of the disinfectant.
  • Following the transfer from the disinfectant, treated test surfaces are incubated in the neutralizing growth medium at a temperature and for a period of time appropriate for the fungus.
  • After incubation, the number of tubes showing growth of the target microorganism is recorded.  To “pass” a 10-carrier test, complete disinfection must take place on all test surfaces. For 60-carrier tests, one carrier may show survival of the test organism.

Strengths of the Germicidal Spray Test Method Modified for Fungi
  • The AOAC Germicidal Spray Products Test is approved by the EPA for data submission in conjunction with registration of spray (aerosol/trigger-spray) disinfectants sold in the USA.
  • The AOAC Germicidal Spray Products Test is a “high-level” test for spray disinfectants, meaning that they must have appreciable biocidal (germ-killing) activity on a relatively short (<10 minutes) time frame to “pass” the test.

Weaknesses of the Germicidal Spray Test Method Modified for Fungi
  • The AOAC Germicidal Spray Products Test Method is fundamentally similar to the AOAC Use-Dilution Test and is variable on the basis of statistics alone (a product that produces a “passing” 1+/60 on average will fail the test some appreciable percentage of the time).
  • This method is subject to additional variability resulting from ambiguities of the official method. For example, the official test method does not address important parameters, such as humidity level during drying of the glass test surfaces.
  • While certainly less removed from “real-life usage” than the AOAC Use-Dilution Test, the AOAC Germicidal Spray Products Test (even when modified for fungi) is a somewhat unrealistic test model. Specifically, products undergoing testing are applied to the contaminated surfaces in large volumes relative to the amount of surface area, causing the product to “pool” on the test slides. If a consumer were to use the same volume of product per unit of surface area that is used in the test, then they would literally require gallons of product to disinfect their kitchen!

Microchem Laboratory has put a great deal of time and thought into perfecting the way we execute antimicrobial efficacy testing. We take many measures to reduce test-to-test variability and are confident that testing generated by the laboratory for the purposes of substantiating a fungicidal efficacy claim are dependable. If your firm is interested in setting up a study with the lab, simply contact us or request a price quote.