~ 41 ~ American Journal of Essential Oils and Natural Products 2014; 2 (1): 41-46 ISSN: 2321 9114 AJEONP 2014; 2 (1): 41-46 © 2014 AkiNik Publications Received: 03-07-2014 Accepted: 20-08-2014 Oladipupo A . Lawal Natural Products Research Uni t, Department of Chemistry, Faculty of Science, Lagos State University, PM B 0001 LA SU Post Office, Ojo, Lagos, Nigeria. Isiaka A . Ogunwande Natural Products Research Uni t, Department of Chemistry, Faculty of Science, Lagos State University, PM B 0001 LA SU Post Office, Ojo, Lagos, Nigeria. Oluwole E. Omikorede Natural Products Research Uni t, Department of Chemistry, Faculty of Science, Lagos State University, PM B 0001 LA SU Post Office, Ojo, Lagos, Nigeria. Moses S. Owolabi Natural Products Research Uni t, Department of Chemistry, Faculty of Science, Lagos State University, PM B 0001 LA SU Post Office, Ojo, Lagos, Nigeria. Felicia F. Olorunsola Natural Products Research Uni t, Department of Chemistry, Faculty of Science, Lagos State University, PM B 0001 LA SU Post Office, Ojo, Lagos, Nigeria. Adetayo A. Sanni Department of Botany, F aculty of Science Lagos State University Department, Ojo, Lagos, Nigeria. Kehinde O. Amisu Department of Microbiology, Faculty of Science Lagos State University Department, Ojo, Lagos, Nigeria. Andy R. Opoku Department of Biochemistry & Microbiology, University of Zululand, K waDlangezwa 3886, South Africa. Correspondence: Oladipupo A . Level Natural Products Research Unit, Department of Chemistry, Faculty of Science, Lagos State University, PMB 0001 LASU Post Office, Ojo, Lagos, Nigeria. Email: jumobi.lawal@ lasu.edu.ng Chemical composition and antimicrobial activity of essential oil of Ocimum kilimandscharicum (R. Br.) Guerke: A new chemotype Oladipupo A. Lawal, Isiaka A. Ogunwande, Oluwole E. Omikorede, Moses S. Owolabi, Felicia F. Olorunsola, Adetayo A. Sanni, Kehinde O. Amisu and Andy R. Opoku Abstract The hydrodistilled essential oils from the flowers and leaves of Ocimum kilimandscharicum (R. Br.) Guerke growing in Nigeria were analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC/MS). Nineteen and thirteen constituents representing 98.0% and 99.6% of the flower and leaf oils were identified, respectively. The major components of the flower oil were methyl eugenol (40.4%), borneol (11.9%) and linalool (10.6%) while the leaf oil consisted mainly of methyl eugenol (53.9%) and -cadinene (16.2%). The antimicrobial activities of the oils were assayed against 12 local bacterial isolates and one reference bacterium using agar-disc diffusion and microdilution-broth methods. The results showed that the oils exhibited a wide range of antimicrobial activities. The mean zones of inhibition (IZ) ranged between 7.3 ± 1.5 and 15.1 ± 1.5 mm in the flower; and 9.3 ± 1.7 and 24.7 ± 1.0 mm in the leaf. The minimum inhibitory concentrations (MIC) values varied between 1.25 and 10 mg/mL (flower) and between 0.16 and 10 mg/mL (leaf). A new chemotype of essential oil of Ocimum kilimandscharicum is described. Keywords: Ocimum kilimandscharicum, Lamiaceae, essential oil composition, methyl eugenol, antimicrobial activity. 1. Introduction Ocimum kilimandscharicum (R. Br.) Guerke, (Lamiaceae) is native to East Africa and cultivated in other parts of the world. This species has a strong but less pleasant flavor. It is an aromatic under shrub with pubescent quadrangular branchlets. This plant is easily recognized by its shrubby habit, growing up to 2.44 m tall [1] . It has pale yellow flowers while the leaves are ovate [2] . This plant attracted attention as a source of camphor. In traditional medicine, this plant is widely used for the treatment of various ailments, including colds, coughs, abdominal pains, measles and diarrhea. The leaves have found use in the treatment of congested chest, cough and cold as well as a cure for measles [2] . Extracts of the plant have been shown to possess wound healing [3] , antioxidant [4] , anti- diarrheal [5] , antibacterial [6] , antinociceptive [7] and antiamnesic [8] activities. In addition, it has insect repellent [9] , mosquito repellent [10, 11] and oviposition deterrence [11] activities. The essential oil was found to be toxic to insect pests [12-14] and possess antibacterial activities [15, 16] . The chemical constituents of O. kilimandscharicum populations grown in different parts of the world have been investigated by many researchers. The main compounds of its volatile oils include camphor [5, 12, 17-22, 24, 32-35] , -pinene [34] , 1,8-cineole [19, 22, 23, 29, 31-35] , linalool [19, 22, 23, 30] , limonene [5, 26, 28, 30] , eugenol [30, 34] , methyl chavicol [30] , β-bisabolene [30] and () -- bisabolene [30] . In continuation of our studies on the chemical composition of essential oils from aromatic and medicinal plants growing in Nigeria [36] , the present investigation reports the chemical composition and antimicrobial activity of essential oils of O. kilimandscharicum growing in Lagos, Nigeria.