Essential oil composition and antimicrobial potential of aromatic plants grown in the mid-hill conditions of the Western Himalayas

Essential oils are highly concentrated natural extracts obtained from plants, rich in bioactive constituents with antimicrobial properties, but the distinctive climate of the Western Himalayan region influences the same. Aromatic and medicinal plants, viz., Origanum majorana, Origanum vulgare, Cymbopogon winterianus, Pelargonium graveolens, and Nepeta cataria were grown in the foothills of the Western Himalayan condition and evaluated for essential oil content, composition, and their effect on some of the most common pathogenic microorganisms. The essential oil content (%) was 0.77, 0.45, 1.37, 0.15 and 0.17% in O. majorana, O. vulgare, C. winterianus, P. graveolens, and N. cataria, respectively. The major essential oil constituents of the isolated oils were terpinen-4-ol, thymol, citronellal, citronellol, and nepetalactone, contributing 41.24%, 31.81%, 43.13%, 43.35% and 91.43% in O. majorana, O. vulgare, C. winterianus, P. graveolens, and N. cataria, respectively. Well-diffusion assay revealed that the essential oil of O. majorana and O. vulgare was active against both the tested Gram-positive, viz., Bacillus subtilis MTCC 121, Micrococcus luteus MTCC 2470, and Staphylococcus aureus MTCC 96; and Gram-negative, viz., Escherichia coli MTCC 43, Klebsiella pneumoniae MTCC 109, and Pseudomonas aeruginosa MTCC 2453 bacteria, while the essential oil of C. winterianus, P. graveolens, and N. cataria showed activity against only some Gram-positive bacteria. Minimum inhibitory concentration (v/v) values indicated the highest efficacy of O. majorana essential oil against B. subtilis (0.5%), M. luteus (1%), and S. aureus (1%), while O. vulgare was most efficient to E. coli (2%) and K. pneumoniae (2%). C. winterianus essential oil did not inhibit any bacterial strains. M. luteus was susceptible to the essential oil of P. graveolens (1%) and N. cataria (0.5%) at low concentrations. Present findings showed the association between the chemical constituents' profile of isolated essential oils from the Himalayan region and their antimicrobial activity, indicating their perspective to be utilized as antibacterial means.