Methods and Guidance for Testing the Efficacy of Antimicrobials against Spores of Clostridium difficile
On September 29, 2017, the U.S. Environmental Protection Agency (EPA) announced the availability of two final test method Standard Operating Procedures (SOP) for evaluating the efficacy of antimicrobials against spores of Clostridium difficile (C. diff):
- EPA Microbiology Laboratory Branch (MLB) SOP MB-28: Procedure for the Production and Storage of Spores of Clostridium difficile for Use in the Efficacy Evaluation of Antimicrobial Agents; and
- EPA MLB SOP MB-31: Procedure for the OECD Quantitative Method for Testing Antimicrobial Products against Spores of Clostridium difficile (ATCC 43598) on Inanimate, Hard, Non-porous Surfaces.
EPA also released regulatory guidance for test criteria and pesticide claims for these products, specifically “Methods and Guidance for Testing the Efficacy of Antimicrobial Products Against Spores of Clostridium difficile on Hard Non-Porous Surfaces.” EPA states that these test methods and guidance “provide a framework for registrants who seek to make a claim for antimicrobial pesticide products to control C. difficile spores on hard, non-porous surfaces.”
C. diff is an anaerobic, spore-forming bacterium and a frequent cause of hospital-acquired infections. The spores survive on hard surfaces such as glass, metals, and plastics that are commonly found in health-care settings. Hospitals and other health care facilities often use antimicrobial pesticides to reduce the number of spores on environmental surfaces. Registrants seeking antimicrobial product registrations with claims to control C. diff will need to carefully review these documents as they consider the efficacy data that EPA will likely require to support these claims, as well as the claims that can be made and supported for these products.
EPA MLB SOP MB-28 describes the test methodology for producing and storing standardized spore suspensions of C. diff based on ASTM E2839, Standard Test Method for Production of C. difficile Spores for Use in Efficacy Evaluation of Antimicrobial Agents (ASTM International). A spore suspension should be developed and qualified according to EPA MLB SOP MB-28 before an efficacy evaluation can be performed using method EPA MLB SOP MB-31. EPA MLB SOP MB-31 describes a quantitative method intended for evaluating the sporicidal efficacy of liquid disinfectants against spores of C. diff on inanimate, hard, non-porous surfaces.
EPA solicited comments on the clarity of the test method SOPs and the regulatory guidance in December 2016. EPA received comments from 12 entities. The primary areas of comment included the following:
- Test carrier interaction;
- Additional method validation;
- Verification testing;
- Soil load;
- Use of a standard setting organization to publish test methods;
- Proposed revisions to the guidance document; and
- Proposed revisions to the standard operating procedures.
EPA revised the drafts to incorporate suggested changes. EPA posted its response to those comments in Docket No. EPA-HQ-OPP-2016-0753-0026.
Some of the changes to the guidance document based on submitted comments include clarifying:
- Three batches of test product should be tested on independent test days;
- The inclusion of the three-part soil load is used for all test, control, and test system control carriers; and
- The current document supersedes the previous 2014 guidance document.
The new guidance proposes updated standard label claims and special instructions that are intended to provide greater clarity to the user community.
EPA’s response to comments and other documents associated with this action are available in Docket No. EPA-HQ-OPP-2016-0753 at www.regulations.gov. The methods and guidance also are found on EPA’s Antimicrobial Testing Methods & Procedures Developed by EPA’s Microbiology Laboratory webpage, at the Methods tab as Method IDs MB-28 and MB-31, and at the Guidance tab as Sporicidal Claims Against Clostridium difficile.
C. diff is widely recognized as one of the most common causes of healthcare-acquired infection. C. diff infections, spread by transmission of bacterial spores, have proven difficult to prevent. EPA’s new guidance and test methods are intended to clarify the efficacy standards that pesticide products claiming to reduce C. diff spores must meet, as well as the associated claims that can be made. This guidance should bring more clarity to pesticide registrants seeking to register such products and to healthcare facilities in their identification of registered pesticide products that may help them to reduce C. diff spores and thus help with prevention efforts.