On August 1, 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 antimicrobial pesticides against two biofilm bacteria, Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus):
- EPA Microbiology Laboratory Branch (MLB) SOP MB-19: Growing a Biofilm using the CDC Biofilm Reactor; and
- EPA MLB SOP MB-20: Single Tube Method for Determining the Efficacy of Disinfectants against Bacterial Biofilm.
EPA also released regulatory guidance for test criteria and pesticide claims for these products, specifically Guidance for Testing the Efficacy of Antimicrobial Products Against Biofilms on Hard, Non-Porous Surfaces. Drafts of the SOPs and the guidance were initially released in October 2016 for comment. EPA received comments from nine entities and revised the drafts to incorporate suggested changes. EPA posted its response to those comments in Docket EPA-HQ-OPP-2016-0357.
EPA states that the two methods are adapted from ASTM International (ASTM) standard methods. EPA MLB SOP MB-19 is used to generate the P. aeruginosa or S. aureus biofilm on coupons. EPA MLB SOP MB-20, the Single Tube Method, then is used to determine the effectiveness of an antimicrobial product in reducing bacteria in biofilm on the coupons.
Notable aspects of the test criteria and claims guidelines include:
- The mean log density for the test organisms of 8.0 to 9.5 for P. aeruginosa and 7.5 to 9.0 for S. aureus; and
- Product performance criterion of a minimum 6-log reduction.
The guidance lists several examples of claims for efficacy against public health biofilm that EPA states are acceptable.
EPA MLB SOP MB-20 is designed to evaluate the efficacy of antimicrobial products that are water soluble powders or liquid formulations. If a company wishes to test a different type of product formulation, or test different target microorganisms, or make any other proposed modifications, it would be well advised to submit proposed alternatives to EPA for review and approval. EPA specifically cautions that the current methodologies are intended for data development to support claims for products registered for use on hard, non-porous surfaces and are not suitable for use sites associated with water systems.
The EPA’s Office of Pesticide Programs’ (OPP) regulation of biofilms has been the subject of increasingly intense commercial interest for years and the availability of this testing guidance is welcome news. While not all will agree with the approach, the new guidance is a helpful addition to OPP’s testing guidance portfolio.