title: Inappropriate use of D-values for determining biocidal activity of various antimicrobials.
abstract: The objective of this study was to investigate the application of established D-value calculations to survival curves for various bacteria using the following antimicrobials: acidified sodium chlorite, triclosan, octanoic acid, and sodium hydroxide. D-values can be calculated in 3 ways, a linear regression, an endpoint calculation, or an average of multiple endpoint calculations. The assumption made in calculating a D-value is that the rate of kill follows 1st-order kinetics under specified treatment conditions. Each antimicrobial solution was challenged with approximately 108 CFU/mL of Staphylococcus aureus, Listeria monocytogenes, Salmonella enterica subsp. enterica, and Escherichia coli independently and in triplicate. Test systems were sampled at each of the 10 time points over a period of 7 min, neutralized, pour plated then incubated at 35 °C for 48 h (AOAC official method 960.09). Survival curves using the log-transformed data were calculated using regression analysis. Correlations coefficients for all linear regression analyses ranged between 0.291 and 0.982, with 6 of the 16 different treatment systems having an R2 value below 0.7. Methods used for calculating D-values should lead to the same result if the survival curve in a given condition is linear. The calculated D-values were different using endpoint analysis (Stumbo method), linear regression, and average of multiple endpoints. This study demonstrates the nonlinearity of inactivation curves of antimicrobials. D-value estimations cannot be reliably used to illustrate biocidal activity in antimicrobial test systems.
authors.affiliation: Ecolab Research Center, 655 Lone Oak Drive, Eagan, MN 55121, USA.
authors.forename: Jesse D
authors.initials: JD
authors.lastname: Hines
authors.forename: Pamela J
authors.initials: PJ
authors.lastname: McKelvey
authors.forename: Peter W
authors.initials: PW
authors.lastname: Bodnaruk
mesh_terms: D000465:Algorithms; D000900:Anti-Bacterial Agents / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D002210:Caprylates / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002712:Chlorides / Q000037:antagonists & inhibitors / Q000494:pharmacology; D015169:Colony Count, Microbial; D004202:Disinfectants / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004926:Escherichia coli / Q000187:drug effects; D007700:Kinetics; D008089:Listeria monocytogenes / Q000187:drug effects; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects; D009994:Osmolar Concentration; D019779:Salmonella enterica / Q000187:drug effects; D012973:Sodium Hypochlorite / Q000037:antagonists & inhibitors / Q000494:pharmacology; D013211:Staphylococcus aureus / Q000187:drug effects; D013223:Statistics as Topic; D013885:Thiosulfates / Q000737:chemistry; D014260:Triclosan / Q000037:antagonists & inhibitors / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D002210:Caprylates; D002712:Chlorides; D004202:Disinfectants; D013885:Thiosulfates; D014260:Triclosan; D012973:Sodium Hypochlorite; C017717:sodium thiosulfate; C031492:octanoic acid; C001599:chlorite