ASTM E2197 - QCTII Method for Clostridium difficile

ASTM E2197 - "QCT II" Quantitative Disk Carrier Test

Welcome to Antimicrobial Test Laboratories' resource page for the QCTII test method (ASTM E2197). This method is designed to test bactericidal, fungicidal, sporicidal and virucidal capabilities of liquid germicides on non-porous hard surfaces using a 1 cm diameter brushed stainless steel surface.

Below, you will find a summary of the ASTM E2197 test method, along with some of its strengths and weaknesses. Importantly, the method has been accepted by US EPA to substantiate efficacy claims for disinfectants against endospores of Clostridium difficile.

Note: The information below is presented for educational purposes only. Current, detailed ASTM Methods can be obtained from ASTM.

Summary of Test Method and Important Parameters:

Test Method Summary:

A small volume of test microorganism is added to the center of 1 cm diameter brushed stainless steel disks.
The test microorganism is dried under vacuum at room temperature.
After drying, the carriers are individually placed into the bottom of sterile vessels for testing.
A small volume of test substance is added directly to the center of the carrier (on top of the dried inoculum) and allowed to sit undisturbed for the duration of the exposure period.
A 10ml volume of neutralizer/elution media is added to each vessel and vortexed to elute surviving test microorganism.
The resulting eluent is serially diluted and the remaining volume passed through a membrane filter.
A series of washes are performed to ensure collection of all surviving test microorganism as well as removal of any test substance that might interfere with downstream analyses.
The appropriate dilutions are plated to the appropriate growth agar and the final rinsed membrane filter placed directly on the appropriate growth agar.
A minimum of three inoculated and dried carriers, per test microorganism, are eluted and enumerated to determine the concentration of test microorganism on each carrier.
Log10 and/or percent reduction calculations are performed for each replicate treated with test substance and when compared to the averaged initial numbers control.

Strengths of the AOAC Germicidal Spray Test Method:

ASTM E2197 is a closed test system (no benefit from washing microbes off the carrier), in contrast to methods such as the AOAC Germicidal Spray Test and AOAC Use-Dilution Test.
The brushed carrier finish is a good representation of an environmental surface commonly treated with liquid germicides (hospital, kitchen and industrial surface).
There is reduced test-to-test variability due to method standardization (e.g. test microorganism concentration, inoculation, drying and treatment).

Weaknesses of the Test Method:

Germicides that have previously demonstrated border-line "passing" results when tested using traditional methods may have a difficult time passing due to low volumes of test substance and high concentrations of test microorganism coupled with the lack of agitation, washing and/or wiping in this method.

Antimicrobial Test Laboratories has put a great deal of time and thought into perfecting the way we execute this relatively new, quantitative method. If your firm has interest in finding out how existing registered disinfectants will fare in this new method, we encourage you to get in touch.

For more information about ASTM E2197 QCTII Testing, Contact the Lab Today!