AOAC Germicidal Spray Test

AOAC Germicidal Spray Products Test

Test Method Summary:

	A 48 hour culture of an individual species of bacteria is dried onto a number of clean, sterile glass test surfaces (microscope slides). If the test includes "organic soil load," then the culture is amended with some percentage of organic matter, such as animal serum, before application to the test surfaces.
	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 incubate in the disinfectant (which normally pools, covering the entire surface of the slide) for a specified contact time.
	After the contact time has elapsed, the treated test surfaces are transferred, individually at intervals, to sterile test tubes or jars containing a liquid growth medium that has been amended with chemical agents to immediately neutralize the action of the disinfectant.
	After transfer from the disinfectant, the treated test surfaces are incubated in the neutralizing growth medium for 48 hours.
	After incubation, the number of tubes showing growth of the target microorganism is recorded. To "pass" a 60 carrier test, at least 59 of the 60 surfaces tested must demonstrate complete disinfection (no detectable growth of the target microorganism in the test tubes containing neutralizing growth medium). To "pass" a 10 carrier test, complete disinfection must take place on all test surfaces.

Strengths of the AOAC Germicidal Spray Test Method:

	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 Test Method:

	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).
	The AOAC Germicidal Spray Products Test 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 and standardization of the concentration of bacteria on the glass test surfaces.
	While certainly less removed from "real-life usage" than the AOAC Use-Dilution Test, the AOAC Germicidal Spray Products Test 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! Additionally, usage directions specifying 10 minute "wet dwell" times (the required dwell time for most products) simply aren't practical and aren't adhered to by the vast majority of consumers of spray disinfectant products.

Antimicrobial Test Laboratories has put a great deal of time and thought into perfecting the way we execute the AOAC Germicidal Spray Test method. We take many measures to reduce test-to-test variability, and often recommend the method as a high-level screen for spray disinfectant products being considered for registration with the EPA or claim optimization in the United States.

For more information about AOAC Germicidal Spray Testing, Contact the Lab Today!