In vitro antimicrobial potential of crude extracts and chemical compositions of essential oils of leaves of Mentha piperita L native to the Sultanate of Oman

Volatile oils of Mentha piperita L (M. piperita) contain various chemical constituents. The aim of this work is to isolate essential oil from leaves of M. piperita, which is native to the Sultanate of Oman, by steam distillation and to analyse chemical constituents by gas chromatography-mass spectroscopy (GC-MS). Fourteen main chemical compounds, representing 91.11% of the leaf oils, were identified in essential oils as carvone (34.94%), pulegone (14.89%), methyl petroselinate (15.51%), d-limonene (11.20%), ρ-cineole (5.70%), methyl isoheptadecanoate (2.35%), 1-tridecene (2.21%), methylene-6,10,10-trimethylbicyclo (7.2.0), undec-5-ene (0.91%) and isopulegone (0.89%). Some minor chemical compounds were also obtained (verbenone (0.72%), β-myrcene (0.57%), β.-pinene (0.73%), sabinene (0.49%) and α-pinene (0.49%)). The extracted methanol extract of M. piperita and its fractions of hexane, chloroform, ethyl acetate, and butanol extracts as well as essential oil were tested for antimicrobial activity via disc diffusion. The crude extracts and essential oils exhibited moderate antibacterial activity against the tested bacteria (e.g., Gram positive Staphylococcus aureus (S. aureus), Gram negative Escherichia coli (E. coli) and Xanthomonas campestris (X. campestris)) within a range of 0-14%. Our findings demonstrate that leaf extracts and essential oils of M. piperita exhibit excellent antimicrobial activity and thus have strong potential as a source of natural antibiotics.