Antimicrobial activity and the major components of the essential oil ofPlectranthus cylindraceus

Abstract

The traditional uses of the aerial parts of fresh Plectranthus cylindraceus by the Dhofaris in Oman were investigated on the basis of antimicrobial properties and composition of its herb oil. The minimal inhibitory concentration (MIC) values of the herb oil of P. cylindraceus against human pathogenic bacteria and yeast were assessed using the broth microdilution method, and the percentage growth inhibition of fungi was determined according to the poisoned food technique. The oil exhibited good activity against Klebsiella pneumoniae, Staphylococcus aureus, Bacillus subtilis and Candida albicans with MIC values in the range of 7.8-62.5 microg ml(-1) and also inhibited the growth of Microsporum canis, Microsporum gypseum, Trichophyton rubrum, Alternaria alternata, Bipolaris sp., Curvularia lunata, Fusarium oxysporum and Stemphylium solani for about a week at 250 microg ml(-1). The two most abundant components of the oil were identified as carvacrol (46.8%) and alpha-terpinolene (18.2%) based on gas chromatography-mass spectra (GC-MS) and 13C nuclear magnetic resonance (NMR) analyses. The oil has a pleasant odour and showed broad spectrum antimicrobial activity. Such bioactivity could be attributed in part to carvacrol. This study has demonstrated the broad spectrum antimicrobial activity of the herb oil of P. cylindraceus as well as the organic composition of this plant extract. This study provides scientific insight into the ancient practice of utilizing P. cylindraceus as a fragrant disinfectant.