Antimicrobial Testing: Strategies for Assessing Product Activity That Is Not Only Potent but Also Rapid
Antimicrobial activity in a product is generally assessed based on its ability to inhibit or reduce the number of microorganisms. However, antimicrobial effectiveness is determined not only by how strong the effect is, but also by how quickly that effect occurs.
Therefore, observation at a single time point is often insufficient to provide a comprehensive picture of an antimicrobial agent’s performance. An approach that can monitor changes in the number of microorganisms at regular intervals is needed so that the dynamics of antimicrobial activity can be observed more clearly.
Table of Content:
- How Can We Take a Closer Look at the Dynamics of Antimicrobial Activity?
- Advantages and Limitations of the Time-Kill Kinetics Assay
How Can We Take a Closer Look at the Dynamics of Antimicrobial Activity?
The time-kill kinetics assay is a method used to observe how antimicrobial activity changes over time. This method can show whether antimicrobial activity is influenced by concentration, exposure time, or a combination of both.
Thus, the assay not only indicates whethe microbicide activity is present, but also provides insight into how quickly the activity occurs. This information makes the time-kill assay useful for studying the patterns and dynamics of microbicide activity, including those of novel antimicrobial agents and combinations of antimicrobial agents.
Observations at different time points can also provide a clearer picture of antimicrobial activity both before and after 24 hours of exposure. The time-kill assay is performed by exposing the test microorganism to an microbicide agent at a specific concentration for a predetermined period.
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The microorganisms are then incubated under controlled conditions, and samples are collected at several time points to monitor changes in the number of viable microorganisms. Samples collected at each time point are inoculated onto an appropriate growth medium, and the resulting colonies are counted to determine the number of surviving microorganisms.
In this way, changes in the microbial population can be observed progressively rather than being assessed solely based on the final result. The results from each time point are then compared to determine the pattern of microbicide activity throughout the observation period.
If the number of microorganisms continues to decrease, this indicates microbicide activity during the observation period, whereas an increase in the microbial population indicates that growth is still occurring.
Advantages and Limitations of the Time-Kill Kinetics Assay
The time-kill kinetics assay has the advantage of being relatively simple while providing comprehensive information about antimicrobial activity. Unlike methods that assess the outcome at only a single time point, this method monitors changes in the number of microorganisms over multiple time points, allowing us to determine how quickly and to what extent microorganisms are killed or their growth is inhibited.
For example, if the initial bacterial count is 1,000,000 CFU/mL and continues to decrease after 2, 4, 8, and 24 hours, the pattern of this reduction can be observed. Therefore, we can determine not only whether the product has antimicrobial activity, but also how quickly and how that activity develops throughout the testing period.
However, this method requires more time, effort, and resources because samples need to be collected and analyzed at multiple time points. The greater the number of time points included, the more samples, media, and enumeration procedures are required.
The method also does not directly explain the specific mechanism by which an antimicrobial agent kills or inhibits microorganisms. In addition, because the assay is conducted in vitro under controlled conditions, the results may not fully represent the more complex biological environment, including changes in antimicrobial concentrations that may occur in vivo.
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Author: Dherika
Editor: Lina
References
Adusei EBA, Adosraku RK, Oppong-Kyekyeku J, Amengor CDK, Jibira Y. (2019). Resistance modulation action, time-kill kinetics assay, and inhibition of biofilm formation effects of Plumbagin from Plumbago zeylanica Linn. J Trop Med, 2019, 1250645. https://doi.org/10.1155/2019/1250645.
Hossain, T.J. (2024). Methods for Screening and Evaluation of Antimicrobial Activity: A Review of Protocols, Advantages, and Limitations. European Journal of Microbiology and Immunology, 14(2), 97-115. DOI: 10.1556/1886.2024.00035.
