Evaluating in vitro antimicrobial activity of thymol toward hygiene-indicating and pathogenic bacteria

Results of a study of the kinetics of bacterial inhibition by thymol in order to develop appropriate applications for the compound in food systems are presented. A modeling-based approach was used to provide a quantitative description of the antimicrobial activity of thymol toward some foodborne pathogens and hygiene-indicating bacteria, which could be postprocessing contaminants of ready-to-eat meat products. The effect of the active compound on the bacterial growth was assessed from growth kinetics curves and dose-response profiles in a wide range of thymol concentrations, i.e., from 50 to 1,000 ppm. Inhibitory data were produced using a macrodilution methodology based on a turbidimetric technique. Microbial response was discussed in terms of Gompertz's parameters as well as in terms of the active concentration of thymol affecting the growth status of microbial suspension (noninhibitory concentration and MIC). Results suggested that thymol can be successfully used as an alternative antimicrobial to increase the lag time as well as to decrease the maximum value of the growth index as reached in the stationary phase of the growth cycle for all investigated bacteria. Due to their high sensitivity to the antimicrobial stress as observed at sub-MIC, it is arguably a potential use of thymol for assurance of food safety and hygiene in combination with other preservative technologies. A quantitative evaluation of the antimicrobial properties of the active compound was performed using a macrodilution methodology based on a turbidimetric technique to produce inhibitory data. Both the growth kinetics and inhibition profile in a wide range of thymol concentrations were obtained for each test bacterium, mathematically modeled, and analyzed. Noninhibitory concentration and MIC were determined to investigate both the microbial sensibility and resistance toward thymol, and Gompertz's parameters were evaluated to assess the microbial response at each phase of growth cycle. The in vitro-obtained results suggested that thymol may be successfully used as a alternative preservative to increase the lag time as well as to decrease the maximum cell load reached in the stationary phase of growth cycle for all investigated bacteria.