Chemical composition and antibacterial activities of the essential oils of Plectranthus glandulosus and Cinnamomum zeylanicum from Cameroon

Abstract

Two aromatic plants have been selected for chemical investigation on account of their antibacterial activities, Plectranthus glandulosus (fresh leaves) and Cinnamomum zeylanicum (dried leaves). P. glandulosus is used as a medicinal plant, while Cinnamomum zeylanicum is used as a common spice in many recipes in Cameroon. The essential oils of the plants have been obtained by hydrodistillation using a Clevenger type apparatus, the yields of oils are about 0.3% and 2.0% respectively. The essential oil of P. glandulosus contains mainly β-thujone (about 31%), p-cymen-8-ol (about 25%) and neral (about 10%) and the essential oil of C. zeylanicum is characterised by a high percentage of eugenol (85%). These essential oils have been tested against three strains of bacteria, namely Pseudomonas fluorescens. Escherichia coli and Staphylococcus aureus; qualitative tests (diffusion through solid medium) and quantitative tests (dilution method) have been carried out. P. fluorescens shows a higher resistance to the two oils (MIC values not less than 5000 ppm). E. coli is more sensitive to these oils, while against S. aureus the essential oil of C. zeylanicum still shows a high activity (3500 ppm). The antibacterial activities of the essential oils could be attributed to the components eugenol as the active component of C. zeylanicum and β-thujone and p-cymen-4-ol of the essential oil of P. glandulosus.