EPA Test Method for Evaluating the Efficacy of Antimicrobial Surface Coatings

As of 2020, the EPA has published new guidance for supporting claims for several new product use cases, with a primary focus on products that provide residual disinfection efficacy.

One of these pieces of guidance is with respect to products that provide supplemental residual antimicrobial efficacy on surfaces, when used in tandem with approved disinfectants.

EPA BEAD Lab SOP MB-40 is a new test method developed and designed to evaluate the claims of products intending to substantiate a claim for these supplemental residual antimicrobial products.

This new EPA-developed test method was developed to provide guidance for antimicrobial surface coatings, films, impregnated surfaces, and paint products that are intended to be registered as a supplemental antimicrobial product – a new class of products that the EPA is allowing efficacy data for.

For this test method, the product is applied to test surfaces (if applicable) and is allowed to dry/cure as applicable for the product. The test articles then undergo a wear regimen to simulate between 1 and 4 weeks of periodic cleaning and disinfection of the test surfaces with a number of disinfectant solutions. At the end of the wear regimen, the efficacy of the test surfaces to kill 99.9% of microorganisms between 1-2 hours is measured.

Summary of the Method:

• Two lots of test substance are assessed, with differing carrier requirements for each lot tested.
  • The first lot undergoes a more challenging assessment compared to the second lot tested.
• Method-specified organisms are Staphylococcus aureus and Pseudomonas aeruginosa.
• The product is applied and allowed to cure onto 1 x 1 inch brushed stainless steel carriers as directed.
  • Five test carrier replicates are performed for each of the wear regimen treatments performed, in addition to carriers that do not undergo the wear regimen.
• The wear regimen is initiated on the test carriers by abrading the test surfaces at room temperature using sponges that have been allowed to soak with one of three chemical solutions per five carrier set. One carrier set is abraded with a quaternary ammonia-based one-step hospital-grade disinfectant/cleaner, another with a disinfectant utilizing hydrogen peroxide (between 3-6%) and peracetic acid as active ingredients, and a final set with a sodium hypochlorite (bleach) solution at 2000 ppm.
  • A fourth carrier set worn only with a dry sponge is also conducted in parallel.
• A total of 10 alternating wet/dry abrasion cycles are performed to simulate one week of cleaning/disinfection. Abrasion of the surfaces is performed with a verified Gardco abrasion machine. Surfaces are allowed to dry for at least 10 minutes after a wet abrasion and hold for at least 5 minutes following a dry abrasion. Parallel control carriers with no product applied are abraded alongside the treated carriers.
  • For the fourth carrier set, all 10 cycles are performed as dry abrasion cycles.
• Following the conclusion of the wear regimen, the efficacy of the product following the wear regimen is assessed within 7 days of the conclusion of the wear regimen, utilizing a 24±2 hour old culture that is supplemented with a tri-part soil load.
• The efficacy test includes inoculating each treated, abraded surface with test culture and allowing it to sit for the 1-2 hour specified contact time. Following the contact time, the product is inactivated by placing the carrier in an appropriate chemical neutralizer.
• To qualify as a supplemental residual antimicrobial coating, all test carriers (both abraded and unabraded) must reduce the total number of microorganisms by at least 99.9%. Incompatibilities with one of the three chemical solutions utilized during the wear regimen must also be minimal.

Strengths:

• The method attempts to simulate real-word usage by incorporating a simulated cleaning/disinfection regimen utilizing both physical and chemical means.
• The method provides a lot of data to draw conclusions from due to the number of assessments that can be made by comparing reductions from carriers that have/have not undergone the wear regimen.

Weaknesses:

• The repeat abrasion portion of the test represents a significant time and resource investment for the laboratory and considerable technical expertise to be performed correctly and consistently, decreasing the number of laboratories that can undertake the test and increasing the likelihood of lab-to-lab variability.
• Due to the number of manipulations conducted on the test and control surfaces throughout the duration of test, variability from replicate to replicate is sometimes observed.
• While the method does attempt to simulate real-worse use cases, these simulated cleanings/disinfection does not perfectly translate to how the product may be used in a real-world environment.