AOAC Approves, EPA Accepts New Performance Standard and Method Modifications of Use Dilution Test for the Registration of Liquid Disinfectants

Posted on: September 30, 2013

The long awaited performance standard changes and method modifications to the AOAC Use Dilution test methods for the evaluation of Staphylococcus aureus and Pseudomonas aeruginosa have finally been accepted by the United States Environmental Protection Agency (EPA). This announcement comes after the submission and review of a manuscript for consideration to the Journal of AOAC International. The manuscript titled “Use of Statistical Modeling to Reassess the Performance Standard for the AOAC Use-dilution Methods (955.15 and 964.02)” was submitted by Tomosino et al.

The revised method allows for up to 3 positive subcultures when testing against Staphylococcus aureus and up to 6 positive subcultures when testing against Pseudomonas aeruginosa. Additionally, the revision mandates each of the three required batches, for each organism, to be evaluated on separate test days. The performance criteria must be met on each day and it is acceptable for a single laboratory to conduct all testing. Furthermore, the revisions are now accepted by the US EPA for substantiation of efficacy claims of liquid disinfectants. No changes were made to the performance criteria for Salmonella enterica.

The chart below outlines the revised performance standard and test requirements for the AOAC Use Dilution Test.

Method Name Method Number Test Organisms Test Parameters Carrier Count Acceptance Criteria Performance  Criteria for Efficacy
AOAC Official Use Dilution Method 955.15 Staphylococcus aureus

(ATCC 6538)

Three separate batches tested on three independent test days

60 replicate carriers for each test

≤ 10 minute exposure time

Mean Log10 Density

6.0 -7.0*

≤3 positive (growth) carriers out of 60 tested.
964.02 Pseudomonas aeruginosa

(ATCC 15442)

≤6 positive (growth) carriers out of 60 tested.

*For tests where the product passes and the mean Log density value is above 7.0, no retesting is necessary.

The newly published methods in first action status can be downloaded by AOAC members (login required) at the Official Methods of Analysis (OMA) web page.

AOAC Use Dilution Method – Staphylococcus aureus

AOAC Use Dilution Method – Pseudomonas aeruginosa

What Do The AOAC Use Dilution Test Method Modifications Mean For Registrants?

The AOAC Use Dilution Methods 955.15 and 964.02 have been notoriously difficult assays for repeatable product efficacy. The modifications to the methods increases the likelihood for otherwise efficacious prodcuts to pass the assay. ATS Labs performs the official AOAC Use Dilution test method(s) according to these new performance standards. Contact us to discuss your testing needs and to learn how these method modifications.