Relationship of Biocide Concentration and Time on Antimicrobial Killing
المؤلف:
Stefan Riedel, Jeffery A. Hobden, Steve Miller, Stephen A. Morse, Timothy A. Mietzner, Barbara Detrick, Thomas G. Mitchell, Judy A. Sakanari, Peter Hotez, Rojelio Mejia
المصدر:
Jawetz, Melnick, & Adelberg’s Medical Microbiology
الجزء والصفحة:
28e , p64-65
2025-06-24
694
When biocides described previously are used to effect microbial populations, the variables of time and concentration need to be considered. It is commonly observed that the concentration of the substance used is related to the time required to kill a given fraction of the population by the following expression:
Cn t = K (1)
In this equation, C is the biocide concentration, t is the time required to kill a given fraction of the cells, and n and K are constants.
This expression says that, for example, if n = 6 (as it is for phenol), then doubling the concentration of the drug will reduce the time required to achieve the same extent of inactivation 64-fold. That the effectiveness of a biocide varies with the sixth power of the concentration suggests that six molecules of the biocide are required to inactivate a cell, although there is no direct chemical evidence for this conclusion.
To determine the value of n for any biocide, inactivation curves are obtained for each of several concentrations, and the time required at each concentration to inactivate a fixed fraction of the population is determined. For example, let the first concentration used be noted as C1 and the time required to inactivate 99% of the cells be t1 . Similarly, let C2 and t2 be the second concentration and time required to inactivate 99% of the cells. From equation (1), we see that:
( 2)
Solving for n gives:
(3)
Thus, n can be determined by measuring the slope of the line that results when log t is plotted against log C (Figure1). If n is experimentally determined in this manner, K can be determined by substituting observed values for C, t, and n in equation (10).
Fig1. Relationship between biocide concentration (C) and time (t) required to kill a given fraction of a cell population.
Reversal of Biocide Action
In addition to time- and concentration-dependent kinetics, other considerations of biocide activity involve the ability of antimicrobial activity to be reversed. Table 1 summarizes a list of mechanisms that can reverse the activity of biocides. These include agent removal, substrate competition, and agent inactivation. Neutralization of biocides needs to be considered as part of the sterilization/disinfection strategy.
Table1. Examples of Mechanisms That Can Reverse the Activity of Biocides
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