Mathematical modelling of the combined effect of propolis extract and Origanum compactum essential oil on the growth of methicillin resistant Staphylococcus aureus

Abstract

Staphylococcus aureus is a commensal human pathogen responsible of several infectious diseases, especially nosocomial infections. Its rapid spread and ability to resist to environmental conditions make it a serious threat for public health. The aim of this study was to investigate the combined antibacterial effect of propolis extract and Origanum compactum essential (OCEO) against methicillin resistant S. aureus (MRSA), and to build a mathematical model predicting this effect. Propolis and OCEO were collected from the north of Morocco. The minimal inhibitory concentration (MIC) of each product was determined by the microdilution method. The kinetics of MRSA growth was evaluated in absence and in presence of ethanol extract of propolis (EEP) and OCEO, each alone and in combination. The mathematical modelling was made by a polynomial regression. EEP and OCEO showed strong antibacterial activity against MRSA. The MIC of EEP was 0.625 mg/mL and the MIC of OCEO was 1%. The two products showed significant reduction in the growth rate of MRSA, and that as a function of concentration. The combination of EEP and OCEO showed strong synergistic interaction, noticed by growth rate reduction. A mathematical model describing the growth of MRSA in presence of EEP and OCEO was generated. By the negative signs of the coefficients of EEP and OCEO in the linear part, the model confirmed they synergistic interaction. From the obtained results it can be concluded that the combination of propolis extract and O. compactum EO is an interesting approach to control MRSA infections.