killcurve

Kill curve, or killcurve, is a term used in microbiology and pharmacology to describe the rate at which a population of organisms is killed by a stressor such as an antimicrobial agent, heat, or radiation. It is typically represented as a plot of the logarithm (base 10) of viable cells, often colony-forming units (CFU), remaining after exposure versus time. In a standard time-kill experiment, cultures are exposed to a fixed concentration of the agent, samples are taken at intervals, and survivors are enumerated. The resulting curve provides a qualitative and quantitative view of kill kinetics.

Interpretation centers on the curve’s shape. A steep, linear region indicates rapid, constant-rate killing; a lag or shoulder implies an initial delay before killing begins; a tail indicates a subpopulation that resists extinction or persisters. The slope of the linear portion reflects the kill rate, and the overall reduction (e.g., log10 CFU reduction) measures efficacy. In pharmacodynamics, kill curves are used to compare agents, distinguish bactericidal from bacteriostatic activity, and inform dosing strategies. They also help evaluate disinfectants and antiseptics and to study resistance mechanisms and biofilm-associated tolerance.

Limitations include that in vitro kill curves may not predict in vivo outcomes due to pharmacokinetics, immune factors, and environmental complexity. Variants include time-kill curves and models such as first-order decay; deviations from simple kinetics are common in practice.