AUTOMATIC AND RAPID MEASUREMENT OF MICROBIAL SUSPENSION GROWTH PARAMETERS: APPLICATION TO THE EVALUATION OF EFFECTOR AGENTS

Traditional methods of assessing antimicrobial agents give little information about the quantitative effect of an inhibitor or stimulator (effector) upon the growth parameters of microbial suspension. Current methods using conductance and light absorption data have lightened the workload, but they do not go beyond determining the exponential growth rate. We have developed mathematical models which, when combined with data provided by these rapid methods, measure the quantitative effect of an antimicrobial agent upon five characteristic growth parameters of a suspension: adaptation time, specific reduction rate during the adaptation phase, exponential growth rate, maximum cell concentration and specific reduction rate during the stationary phase. In addition, our methods can measure the instantaneous growth rate. This allows real-time studies of the effect of chemical or physical stresses upon subsequent microbial growth. We illustrate some of the applications with examples taken from studies of the antimicrobial effects of certain essential oils and spices upon bacterial suspensions.