EPA 730-N-O1-004
                                            WASHINGTON, D.C. 20460
                                                                            OFFICE OF
                                                                    PREVENTION. PESTICIDES AND
                                                                         TOXIC SUBSTANCES

                    PESTICIDE REGISTRATION (PR) Notice 2001-4


ATTENTION:      Persons Responsible for Federal Registration and Reregistration of
                    Antimicrobial Pesticide Products

SUBJECT:         Elimination of Phenol Resistance Testing for Antimicrobial Disinfectant
                    and Sanitizer Pesticides

       This notice announces the discontinuation of phenol resistance testing as a part of
efficacy testing for antimicrobial disinfectants and sanitizers.  Effective immediately, the Agency
will consider registering or reregistering antimicrobial disinfectant or sanitizer pesticides without
supporting phenol resistance testing. All other data in support of registration or reregistration,
including any required efficacy testing data, must be submitted and then accepted by the Agency.


       Phenol resistance testing is a standard that has traditionally been used to estimate the
intrinsic resistance or sensitivity of some test bacteria to chemical disinfectants and sanitizers.
For years the Agency has been aware of the lack of standard and uniform resistance  levels to
phenol expressed by the test cultures used in the existing Official Methods of Analysis of the
Association of Official Analytical Chemists (AOAC) test methods. Historically, the inability to
maintain and propagate test cultures that express standard and uniform levels of phenol
resistance has been a recognized scientific problem which has persisted for at least 70 years.
Furthermore, the inability of many reputable and competent testing facilities to achieve
consistent test results with the phenol resistance standard has prompted both concern and action
by the Agency.

       On September 10,1997, after internal scientific deliberation, the Agency placed before
the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific Advisory Panel
(SAP) the following question regarding phenol resistance:

       What scientific direction should be taken regarding the lack of standard and
       uniform resistance levels to phenol of the test cultures used in the existing AOAC
       (Association of Official Analytical Chemists) efficacy test methods? Should the

       •Totally eliminate the phenol resistance requirement; or

       •Modify the required phenol resistance patterns to provide a broader range of
       acceptable resistance; or

       •Replace the phenol resistance requirements with some other procedures that
       assure hardiness and equivalence to test cultures, such as standard, quantitative
       inoculum level?

       Briefly, the response provided to the Agency by the SAP was as follows:

       "There is no current relevance to requiring the phenol resistance test; hence (the)
       phenol coefficient method should be eliminated and new protocols should be
       established for defining the conditions for culturing test microorganisms with
       suitable resistance levels to antimicrobials....

       In summary, phenol resistance does not appear to be linked to other germicidal or
       antibiotic (drug) resistance nor is it a good marker of genetic variability or
       similarity.  Furthermore, levels of phenol susceptibility frequently are outside
       current EPA guidelines, resulting in significant expense to industry and

       Quantitative inoculum level is a better choice, if growth and environmental
       conditions suggested for any new methods are considered. However, current
       methodologies for quantitation are not accurate, as they do not take into account
       inadequate removal of microorganisms from natural substrates and the ability of
       the organisms to become more resistant to pH change, oxidation, altered
       temperature, etc.  Research is needed in this area. The Panel recommends that the
       Agency request a consensus approach of available experts who can define
       reproducible tests which model germicidal resistance in nature."


       Subdivision G of the Pesticide Assessment Guidelines, part 91-1, describes the general
product performance (efficacy) standards for disinfectants and sanitizers. Subsection (b)(3)(I) of
part 91-1 refers to the AOAC standard tests that may be used to satisfy the data requirements of
40 CFR 158.640. The following AOAC tests include references to phenol resistance testing.

       Phenol resistance testing procedures and standards appear as a part of AOAC Official
 Method 955.11, Testing Disinfectants against Salmonella typhi, Phenol Coefficient Method
 (Final Action 1964), and are referenced by several other AOAC testing methods. The Phenol
 Coefficient Method (PCM) provides instructions and specifies satisfactory phenol control
 readings for Salmonella typhi (Table 955.1 IB), for Staphylococcus aureus (Table 955.12), and
 for Pseudomonas aeruginosa (Table 955.13). Method 955.14, Testing Disinfectants against
 Salmonella choleraesuis, Use Dilution Method, specifies an expressed phenol resistance
 equivalent to that specified for S. typhi hi the PCM, while method 955.15, Testing Disinfectants
 against Staphylococcus aureus, Use Dilution Method, specifies that expressed phenol resistance
 be the same as that previously specified for this organism in the PCM. There is no phenol
 resistance expression specified for P.  aeruginosa for use in the Use Dilution Method. Method
 955.16, Chlorine (Available) in Disinfectants, Germicidal Equivalent Concentration, specifies
 phenol resistance for either S. typhi or S. aureus by reference to the resistances previously
 specified in the PCM. Method 955.17, Fungal Activity of Disinfectants, specifies the phenol
 resistance for use with Trichophyton mentagrophytes. Method 960.09, Germicidal and Detergent
 Sanitizing Action of Disinfectants specifies phenol resistance of Escherichia coli should be
 equivalent to that specified for S: typhi in the PCM and that for £ aureus equivalent to that
 previously specified in the PCM. Finally, Method 965.12, Tuberculocidal Activity of
 Disinfectants, a carrier based resistance test, specifies a phenol resistance determination for the
 test organism, Mycobacterium bovis, while present on the surface of porcelain penicylinder

       The Agency has reviewed the SAP's recommendation to eliminate, modify, or redirect
the use of phenol resistance testing for antimicrobials. The Agency concurs with the SAP and
has engaged in considerable discussion and deliberation, internally and with members of the
scientific and regulated communities, that phenol resistance expressed by such organisms as S.
typhi (a representative enteric pathogen) and S. aureus (major source of wound infection), when
used as part of the phenol coefficient method, has been an unsatisfactory standard for evaluating
the sensitivity of certain microorganisms used during disinfectant efficacy testing. The phenol
resistance assay does not mimic the test systems in the current efficacy methods.

       The Agency has also considered the recommendation to modify the phenol resistance
patterns currently deemed acceptable, thus changing the established growth/non-growth patterns.
Although this modification would greatly facilitate meeting an acceptable phenol pattern, it
would not solve other inherent problems associated with the use of the phenol resistance test (e.g.
technique sensitive assay, highly variable results, non-carrier based test, disassociation with the
efficacy method.)

       The Agency acknowledges that inoculum titre and quality will influence the outcome of
the efficacy evaluation of an antimicrobial.  The use of a quantitative inoculum level and other

parameters of inoculum quality as suitable indicators of a challenge population is recognized and
should be studied further. As an interim measure, the Agency will generally expect that a
minimum inoculum level of 104 cfu/carrier for all test microorganisms should be achieved when
an AOAC carrier-based test method is used. The inoculum level should be reported with the
efficacy data submission.

       Given the inapplicability of a test organism's resistance to phenol when disinfectants or
sanitizers are tested for their efficacy performance, the Agency will no longer require submission
of testing to demonstrate compliance with AOAC-specified levels of expressed phenol resistance
by test microorganisms during the efficacy evaluation of disinfectants or sanitizers.


       This PR Notice describes the requirements set forth in Agency regulations and FIFRA,
and provides general guidance to EPA and to affected parties as well. While the  requirements
in FIFRA and Agency regulations are binding on EPA and applicants, this notice is intended to
provide guidance to EPA personnel, pesticide registrants and applicants, and the public. As a
guidance document, this policy is not binding on either EPA or any outside parties, and the EPA
may depart from the guidance where circumstances warrant and without prior notice. Registrants
and applicants may propose alternatives to the recommendations described in this notice, and the
Agency will assess them for appropriateness on a case-by-case basis.


       For further information, contact Michele Wingfield at 703-308-6349 or at
                                                7rank '^Sanders, Director
                                               Antimicrobials Division
                                               Office of Pesticide Programs