Surface Disinfectant Efficacy Validation (coupon test)

Validation of sanitizing agents for effectiveness against organisms is increasingly an area of concern to manufacturers and regulatory agencies alike. Two ways to help validate a disinfectant program include testing the disinfectant by performing a time kill procedure of the use dilution in a liquid test matrix, or testing the kill rate after the disinfectant is applied to contaminated surfaces. This test procedure was designed to test the kill rate after a disinfectant is applied to contaminated coupons and is based on the AOAC Official Method 961.02 Germicidal Spray Products, with the exception that this is a quantitative test. Anywhere from three to ten replicates for each combination can be tested upon request.

Study Outline

Representative surfaces that are scaled down for laboratory testing are referred to as coupons. The test coupons must be able to be sterilized prior to testing by either autoclave or ethylene oxide treatment. The sterile coupons are held in sterile petri dishes lined with filter paper to create a sterile environment in which to perform the test. For a challenge, 10-30 µL of culture or spore suspension is applied to the coupon surface, spread evenly over a one square inch area, and then dried for 30-40 minutes. The challenge culture may include an organic soil such as 5% blood serum to further the difficulty of disinfection upon request. The coupons are then dried for 30-40 minutes at 37 ± 2°C.

The actual test procedures involving the disinfectant application onto the coupon surface can vary greatly and are adjustable to suit testing needs. Some examples of disinfectant application include spraying directly or wiping with a sterile towel saturated with the disinfectant. Another aspect to consider is the exposure time that the disinfectant is in contact with the inoculated coupons. Following the disinfection procedure that has been applied, the treated coupons are aseptically transferred to neutralizing media which doubles as a surfactant to remove any surviving microorganisms. Aliquots of the extract fluid are plated in order to quantify the bioburden of each individual coupon. The counts are compared to untreated inoculated coupons that have been extracted in the same manner and the reduction of the challenge organisms is measured in log and percent reduction.

The panel of organisms selected to be used as a challenge in this test can also vary. It is recommended that a spectrum of representative organisms be selected for the test including, but not limited to, Gram positive bacteria, Gram negative bacteria, fungi, mold spores, and Gram positive spore-forming bacteria. Additionally, environmental isolates from your facility can be tested. Some typical examples of challenge microorganisms include Staphylococcus aureus, Klebsiella pneumoniae, Candida albicans, Aspergillus niger, and Bacillus subtilis.

Neutralization validation of the test disinfectants and extraction efficiency testing are included in every test for each organism/disinfectant/coupon combination tested as well as positive and negative controls. Environmental testing and organism identification, although available, are not included in the basic test, but may be added by request.

Sample Requirements

Type 304 stainless steel coupons are kept on hand for stainless steel testing, other surface types must be submitted.  Test coupons should be approximately 1 x 3 inches (3 x 8 cm).  Disinfectants must have MSDS included.

Sample Requirements

Type 304 stainless steel coupons are kept on hand for stainless steel testing, other surface types must be submitted.  Test coupons should be approximately 1 x 3 inches (3 x 8 cm).  Disinfectants must have MSDS included.