In vitro antilisterial effect of essential oils by modeling of growth curve MIC values

Abstract

Background: Listeria monocytogenes is food contaminant being widely tolerant to different environmental factors. It is one of the most frequent causative agents of deaths among foodborne pathogens. Objectives: The aim was to examine the in vitro antilisterial effect of essential oils (EOs) of Juniperus communis and Satureja montana. Methods: EOs were chemically analyzed by GC/GC-MS. Antilisterial effect against ATCC19111 strain and three primoisolates was determined in microdilution, checkerboard and time-kill assays. Results of time-kill assay were used not only to analyze the type of interaction between EOs, but also to determine the growth rates of curves obtained for different concentrations of test substances. By plotting of growth rates as a function of applied concentrations, growth curve MIC was determined as the concentration inducing neither the progression nor the regression of bacterial population. Results: MIC values determined in microdilution assay and by modeling of time-kill assay growth curves were in the ranges 0.5-1% and 0.03-0.14%, respectively. Multifold higher values of MIC obtained in microdilution assay could be addressed to the feature that L. monocytogenes is more resistant to different stressors in reduced oxygen environment. In addition, synergism of both EOs in mixture treatment of isolates was determined in checkerboard and time-kill assays. In conclusion, J. communis and S. montana EOs and their combinations could be the efficient inhibitors of the L. monocytogenes growth. However, the fact that its susceptibility to antimicrobials is influenced with environmental conditions requires the use of different experimental approaches in order to better explore it.