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EPA Proposes to Eliminate Phenol Resistance as Part of Antimicrobial Efficacy Testing

Date: Dec 07, 2000


The Environmental Protection Agency (EPA) recently proposed to eliminate a long-standing requirement that efficacy testing for antimicrobial disinfectants and sanitizers include phenol resistance testing.

Phenol has been used to measure the intrinsic resistance or sensitivity of test organisms used in antimicrobial efficacy testing. For example, a particular test organism might be expected to survive five minutes of exposure to a dilute phenol solution, but not survive 15 minutes of exposure. This testing is intended to establish that the test organisms are not excessively sensitive or resistant to antimicrobial agents. Directions for phenol resistance testing are included in the current protocols for efficacy testing of disinfectants published by the Association of Official Analytical Chemists (AOAC). The AOAC test methods are referenced in EPA's Pesticide Assessment Guidelines.

Under EPA's recent proposal, the agency will no longer require phenol resistance testing. In its place, EPA notes that it will generally expect that a minimum inoculum level of 1000 colony forming units (CFU) per carrier be demonstrated for all test organisms when an AOAC carrier-based method is used.

The regulated community and microbiological testing laboratories in particular regard this as a welcome development. The value of phenol resistance testing as an indication of antimicrobial resistance has long been questioned, and laboratories have found it difficult to grow test organisms that exhibit the required level of phenol resistance.

We note that EPA generally requires efficacy testing to support registration of an antimicrobial pesticide that will be used to control human pathogens. Efficacy testing is not required for all antimicrobials. We also note that other federal agencies such as the Food and Drug Administration, and even state agencies, such as California's Department of Pesticide Regulation, may continue to expect phenol resistance testing as part of antimicrobial efficacy testing. Therefore, data submitters should pay attention to the possibility of varying requirements in this area.

EPA is accepting comments on its proposal, which takes the form of a draft Pesticide Registration (PR) Notice, through January 8, 2001. Anyone looking for more information may contact David Joy at 202-434-4126 or at joy@khlaw.com.