EPA Test Method for the Continuous Reduction of Bacterial Contamination on Copper Alloy Surfaces

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The EPA’s “Test Method for the Continuous Reduction of Bacterial Contamination on Copper Alloy Surfaces” is designed to quantitatively test the ability of copper alloy surfaces to continuously reduce bacterial inoculums on these surfaces. It is a difficult test for most antimicrobial surfaces to pass. In order to obtain a “continuous reduction” claim, an initial sanitizer evaluation must be performed. 

The method was written with copper surfaces in mind, to substantiate “continuous reduction” claims for microorganisms of public health concern. However, it can be easily modified for use with other types of surfaces, and the EPA considers it to be the technical basis for subtantiation of all “continous reduction” claims for antimicrobial surfaces.

Summary of the Continuous Reduction of Bacterial Contamination Method
  • The test surface must pass the EPA’s “Test Method for Efficacy of Copper Alloy Surfaces as a Sanitizer” prior to testing for “Continuous Reduction”.
  • The test culture is prepared from stock cultures by incubation in appropriate broth. 
  • The suspension of test culture is then standardized by dilution in broth and organic soil is added to simulate “dirty” conditions. 
  • Pre-cut, cleaned and sterilized test and control surfaces are inoculated with the standardized test microorganism.
  • Carriers are set to be harvested at different time points, accumulating bacterial load through re-inoculation at specified time intervals. Longer intervals accumulate more bacterial load vs. shorter intervals by way of re-inoculation.
  • Following the pre-specified time intervals, carriers are eluted, diluted and plated to determine the concentrations of viable test microorganisms on the surface.
  • For the test sample to be defined as a surface that continuously reduces bacteria, a minimum of a 90% reduction in bacteria, compared to that present on the control surface, must be achieved at all time intervals over the 24 hour inoculation and exposure period.

Strengths of the Continuous Reduction of Bacterial Contamination Method
  • The method is quantitative, allowing for clear pass/fail criteria.
  • Test microorganism concentrations are standardized, thus increasing reproducibility among tests, samples and technologies.
  • Test microorganisms are provided with nutrients during the contact time(s) thus resulting in a robust challenge for surfaces that meet the method requirements for testing.
  • The method is representative of actual surface contamination events since it involves numerous re-inoculations throughout the procedure.

Weaknesses of the Continuous Reduction of Bacterial Contamination Method
  • Test sample composition as stated in the title of the method is specific to copper and copper alloy technologies, so Sponsors must be aware that EPA will likely required pre-approval of a protocol for testing of non-copper surfaces.
  • The method has strict guidelines regarding test samples and those tested should not be waxed, painted, lacquered, varnished, or otherwise coated; thereby limiting the type of treatment that can be applied to a sample. 
  • Label claims supported by this method are limited to indoor, hard, non-porous surfaces where cleaning practices are consistent.

Microchem Laboratory has become a leader in the industry with regard to the testing of antimicrobial surfaces. The EPA’s issuance of the so-called “copper methods” represents a step forward in the regulation of antimicrobial surfaces that benefit public health.