The EPA pre-saturated towelette disinfection test method is used to substantiate efficacy claims for disinfectant towelettes.
This method is a modification of the AOAC Germicidal Spray Products Test for Disinfectants. Instead of contaminated test surfaces being sprayed with disinfectant as in the germicidal spray products test, they are wiped with a disinfectant towelette.
Summary of the Germicidal Towelettes Test Method
- 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 wiped, individually, with the pre-saturated towelettes in accordance with manufacturer instructions and in light of EPA guidance regarding the number of test surfaces that must be treated with a single pre-saturated towelette. Depending on the purpose of the test, either 10 or 60 contaminated test surfaces may be treated in all with the pre-saturated disinfectant towelettes.
- After the test surfaces are wiped with the towelette, they are allowed to rest (usually in a petri dish) for the remainder of the contact time specified by the study sponsor.
- 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 present on the pre-saturated towelette.
- 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 wiped with the towelettes 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 of the wiped test surfaces.
Strengths of the AOAC Germicidal Towelettes Test Method
- The pre-saturated towelette method put forth by EPA is approved by the EPA for data submission in conjunction with disinfectant towelettes sold in the USA.
- The pre-saturated towelette method is a “high-level” test for germicidal wipes, 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 Towelettes Test Method:
- The EPA Pre-Saturated Germicidal Towelette Test Method is fundamentally similar to the AOAC Germicidal Spray Product 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 EPA Pre-Saturated Germicidal Towelette Test 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 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 EPA Pre-Saturated Germicidal Towelette Test Method is a somewhat unrealistic test model. Specifically, one wipe is generally used to treat (10) contaminated glass slides, and virtually all of the impregnated liquid is expunged during this process. Thus, one wipe must treat only 30 square inches of contaminated surface – less than 1/4 of a square foot.
- Since the pressure and technique used to treat the surfaces with the pre-saturated towelettes varies widely from lab to lab, variability may be higher than desired.
Microchem Laboratory has put a great deal of time and thought into perfecting the way we execute the EPA Pre-Saturated Germicidal Towelette Test Method. We take many measures to reduce test-to-test variability.