EXTRACTS OF ROSMARINUS OFFICINALIS, RHEUM RHAPONTICUM, AND ORIGANUM MAJORANA EXHIBIT SIGNIFICANT ANTI-STAPHYLOCOCCAL ACTIVITY

Background: Bacterial resistance to antimicrobial agents is on the rise and this is causing serious complications resulting in increased morbidity and mortality of bacterial infections. There is a need for new antimicrobial molecules in order to fight against Multi-Drug-Resistant Organisms. The Mediterranean area is rich in a variety of medicinal plants and this may represent a potential for new compounds and molecules with enhanced antibacterial activity.

Methods: The antimicrobial effects of three traditionally used Lebanese plants were investigated against 24 clinical isolates of Staphylococcus aureus with different phenotypes of resistance. Rosmarinus officinalis, Rheum rhaponticum, and Origanum majorana where extracted with ethanol, then further subfractionated with petroleum ether, dichloromethane and ethyl acetate. The remaining aqueous fraction was also collected, thus a total of five extracts were studied for each plant. The MIC and MBC of these extracts were determined using the micro-dilution technique.

Results: Rosmarinus officinalis was the most effective against most of the strains studied including MRSA, QS, QR, MS and MR. The ethyl acetate fraction of Rosmarinus officinalis, Rheum rhaponticum, and Origanum majorana showed significant antibacterial activity against S. aureus with MIC ranging between 2.5 and 5µg/µl. The crude extract of Rheum rhaponticum was also highly effective at a low concentration of 4.25µg/µl.

Conclusions: Most extracts showed antimicrobial activity at low concentrations. Antimicrobial activity of the plant extracts varied with the profile of resistance of the bacterial isolate. Further studies need to investigate the active compounds in these extracts and their mode of action to make use of them as antibiotics and food preservatives.