Antimicrobial activity of three Lebanese plant extracts on clinical isolates of Staphylococcus aureus with different profiles of resistance

Abstract

The antimicrobial effect 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 final fraction was the aqueous, making a total of five extracts studied for each plant. The MIC and MBC of these extracts were determined using the microdilution technique. All extracts showed antimicrobial effect at low concentrations except petroleum ether extract of Rheum rhaponticum which had no effect against Staphylococcus aureus at the tested concentrations. Plant extracts varied in their antimicrobial effect with the difference of bacterial resistance. Rosmarinus officinalis was the most effective against most of the strains including MRSA, QS, QR, MS and MR. The ethyl acetate of Rosmarinus officinalis, Rheum rhaponticum, and Origanum majorana showed significant antibacterial activity against S. aureus with MIC ranging between 2.5 and 5 µg/µl. The crude extract of Rheum rhaponticum was also highly effective at a low concentration of 4.25 µg/µl. 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.