Time-kill studies are in vitro assays used to evaluate the bactericidal activity of antimicrobial agents by measuring changes in bacterial counts over time in the presence of a defined drug concentration.
They provide dynamic information on the rate and extent of bacterial killing, typically expressed as a reduction in colony-forming units (CFU) per millilitre at specified time points compared to a baseline inoculum. A ≥3 log₁₀ CFU/mL reduction from the starting inoculum is generally considered evidence of bactericidal activity. These studies are widely applied in antimicrobial research to assess pharmacodynamic properties, characterize drug potency, and inform dosing strategies.
In addition to single-agent evaluations, synergy time-kill studies are performed by combining two or more agents to determine whether the interaction produces enhanced killing (synergy) compared to each drug alone.
Time-kill studies are valued for their ability to mimic clinically relevant drug exposures and provide insights into bacterial regrowth, persistence, and resistance development. However, they are labour-intensive and require careful standardization of inoculum size, drug concentrations, sampling intervals, and media conditions to ensure reproducibility.