Every year there are millions of cases of diseases caused by food pathogens. Therefore, food safety is one of the most important challenges in the food industry. One of the most important pathogens is Listeria monocytogenes, due to the high mortality and its high resistance against conventional methods of conservation. High hydrostatic pressure (HHP) treatment is an efficient method with good prospects of implementation in the food industry. In this project, the effects of HHP sublethal treatment on cultures of different strains of Listeria monocytogenes were analysed through mathematical methods. The experimental data used in this project were obtained mainly by Bioscreen. The experimental work was performed in the installations of IRTA, at Monells. Particularly, an innovative methodology was developed, which consists of the calibration of data obtained through absorbance (optical density) with data obtained from plate cultures (CFU). In order to study the effect of an HHP treatment, the goodness of the three analysis methods were evaluated: (1) using direct data of optical density, (2) 2-fold dilution method and (3) CFU obtained from calibration with optical density. The advantages and drawbacks of each method were analyzed. This study shows the interest to keep working on the improvement of the method based on the calibration of data obtained from optical density.