Antibacterial Activities of Essential Oils from Three Medicinal Plants in Combination with EDTA against Methicillin-resistant Staphylococcus aureus

Aims: To determine the antibacterial activity of essential oils (EOs) from Thymus vulgaris L, Origanum vulgare L and Minthostachys mollis (Benth.) Griseb in combination with ethylenediaminetetraacetic acid (EDTA) on methicillin-resistant Staphylococcus aureus (MRSA) from clinical isolates.

Study Design: Collection of plant material, extraction, phytochemical analysis and evaluation of antimicrobial activity of the essential oils.

Place and Duration of Study: Clinical Research Institute, Faculty of Medicine, Universidad Nacional Mayor de San Marcos, Department of Microbiology, Faculty of Pharmacy and Biochemistry, and Department of Microbiology, Hospital Dos de Mayo, Lima, Peru, between February 2014 and February 2015.

Methodology: The EOs’ chemical composition was determined by gas chromatography coupled with mass spectroscopy (GC-MS). Clinical isolates of MRSA were obtained from the “Dos de Mayo” National Hospital in Lima, Peru. The inhibitory activity on MRSA was determined by disk diffusion method and Minimum inhibitory concentration (MIC) by the microdilution colorimetric method in 96-well plates. All statistical analysis was performed using SPSS V 21.0 software.

Results: The main components of Thymus vulgaris EO were thymol (46.47%), γ-terpinene (20.27%) and p-cymene (15.80%); from Origanum vulgare EO were γ-terpinene (21.17%), (-)-4-terpineol (12.61%) and cis-β-terpineol (12.18%); and from Minthostachys mollis EO were pulegone (33.48%) and menthone (26.68%). The Thymus vulgaris EO presented inhibition halo diameters of 32.23 ± 1.70 mm, and Thymus vulgaris + EDTA had inhibition halo diameters of 32.47 ± 2.06 mm, both significantly higher compared to 30 mcg of cefoxitin, which had inhibition halo diameters of 17.60 ± 0.68 mm (p < .01). The MIC of T. vulgaris against MRSA was 0.57 µg/mL. Origanum vulgare and Minthostachys mollis EOs were resistant to MRSA.

Conclusion: This study showed that the Thymus vulgaris essential oil had antibacterial activities against MRSA and indicates their potential application in the control of this pathogen commonly known for their resistant activities to most conventional antibiotics.