title: Procedural revision to the use-dilution methods: establishment of maximum log density value for test microbes on inoculated carriers.
abstract: (Staphylococcus aureus) and 964.02 (Pseudomonas aeruginosa), were revised in 2009 to include a standardized procedure to measure the log density of the test microbe and to establish a minimum mean log density value of 6.0 (geometric mean of 1.0 x 10(6) CFU/carrier) to qualify the test results. This report proposes setting a maximum mean log density value of 7.0 (geometric mean of 1.0 x 10(7) CFU/carrier) to further standardize the procedure. The minimum value was based on carrier count data collected by four laboratories over an 8-year period (1999-2006). The data have been updated to include an additional 4 years' worth of data (2006-2010) collected by the same laboratories. A total of 512 tests were conducted on products bearing claims against P. aeruginosa and S. aureus with and without an organic soil load (OSL) added to the inoculum (as specified on the product label claim). Six carriers were assayed in each test, for a total of 3072 carriers. Mean log densities for each of the 512 tests were at least 6.0. With the exception of two tests, one for P. aeruginosa without OSL and one for S. aureus with OSL, the mean log densities did not exceed 7.5 (geometric mean of 3.2 x 10(7) CFU/carrier). Across microbes and OSL treatments, the mean log density (+/- SEM) was 6.80 (+/- 0.07) per carrier (a geometric mean of 6.32 x 10(6) CFUlcarrier) and acceptable repeatability (0.28) and reproducibility (0.31) SDs were exhibited. A maximum mean log density per carrier of 7.0 is being proposed here as a validity requirement for S. aureus and P. aeruginosa. A modification to the method to allow for dilution of the final test cultures to achieve carrier counts within 6.0-7.0 logs is also being proposed. Establishing a range of 6.0-7.0 logs will help improve the reliability of the method and should allow for more consistent results within and among laboratories.
authors.affiliation: U.S. Environmental Protection Agency, Office of Pesticide Programs, Biological and Economic Analysis Division, Microbiology Laboratory Branch, Environmental Science Center, Fort Meade, MD 20755-5350, USA. Tomasino.Stephen@epa.gov
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Tomasino
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Pines
authors.forename: Gordon C
authors.initials: GC
authors.lastname: Hamilton
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D002623:Chemistry Techniques, Analytical / Q000379:methods* / Q000592:standards; D002626:Chemistry, Pharmaceutical / Q000379:methods; D004341:Drug Evaluation / Q000379:methods*; D008826:Microbial Sensitivity Tests / Q000379:methods* / Q000592:standards; D008828:Microbiological Techniques; D011550:Pseudomonas aeruginosa / Q000378:metabolism; D015203:Reproducibility of Results; D012988:Soil Microbiology; D013211:Staphylococcus aureus / Q000378:metabolism; D013234:Stem Cells; D013997:Time Factors
chemical_list: D000890:Anti-Infective Agents