title: The Integral Method, a new approach to quantify bactericidal activity.
abstract: The bactericidal activity (BA) of antimicrobial agents is generally derived from the results of killing assays. A reliable quantitative characterization and particularly a comparison of these substances, however, are impossible with this information. We here propose a new method that takes into account the course of the complete killing curve for assaying BA and that allows a clear-cut quantitative comparison of antimicrobial agents with only one number. The new Integral Method, based on the reciprocal area below the killing curve, reliably calculates an average BA [log10 CFU/min] and, by implementation of the agent's concentration C, the average specific bactericidal activity SBA=BA/C [log10 CFU/min/mM]. Based on experimental killing data, the pertaining BA and SBA values of exemplary active halogen compounds were established, allowing quantitative assertions. N-chlorotaurine (NCT), chloramine T (CAT), monochloramine (NH2Cl), and iodine (I2) showed extremely diverging SBA values of 0.0020±0.0005, 1.11±0.15, 3.49±0.22, and 291±137log10 CFU/min/mM, respectively, against Staphylococcus aureus. This immediately demonstrates an approximately 550-fold stronger activity of CAT, 1730-fold of NH2Cl, and 150,000-fold of I2 compared to NCT. The inferred quantitative assertions and conclusions prove the new method suitable for characterizing bactericidal activity. Its application comprises the effect of defined agents on various bacteria, the consequence of temperature shifts, the influence of varying drug structure, dose-effect relationships, ranking of isosteric agents, comparison of competing commercial antimicrobial formulations, and the effect of additives.
authors.affiliation: Department of Hygiene, Microbiology and Social Medicine, Division of Hygiene and Medical Microbiology, Medical University of Innsbruck, Schöpfstr. 41, A-6020 Innsbruck, Austria.
authors.forename: Waldemar
authors.initials: W
authors.lastname: Gottardi
authors.affiliation: Institute of Astro- and Particle Physics, Leopold-Franzens University of Innsbruck, Technikerstr. 20, A-6020 Innsbruck, Austria.
authors.forename: Jörg
authors.initials: J
authors.lastname: Pfleiderer
authors.affiliation: Department of Hygiene, Microbiology and Social Medicine, Division of Hygiene and Medical Microbiology, Medical University of Innsbruck, Schöpfstr. 41, A-6020 Innsbruck, Austria. Electronic address: m.nagl@i-med.ac.at.
authors.forename: Markus
authors.initials: M
authors.lastname: Nagl
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D007700:Kinetics; D008826:Microbial Sensitivity Tests / Q000295:instrumentation / Q000379:methods*; D013211:Staphylococcus aureus / Q000737:chemistry / Q000187:drug effects* / Q000254:growth & development
chemical_list: D000900:Anti-Bacterial Agents
keywords: Antimicrobial agents; Antiseptic; Disinfection; Killing curve; Quantitative killing assay; Specific bactericidal activity