Abstract Cleome viscosa L. (Cleomaceae) is an annual herb that is widely distributed in the tropical and warm temperate regions. It has many ethnomedicinal, ethnobotanical and economic importance. This study investigated the essential oil constituents and antimicrobial activity of C. viscosa whole plant due to scarcity of information on these properties. The essential oil from thewhole plant was extracted by hydrodistillation and characterised using Gas Chromatography (GC) and Gas Chromatography- Mass Spectrometry (GC-MS) techniques. The components of the essential oil were identified based on retention indices and comparison with published spectra. The agar-well diffusion technique was used for the antimicrobial screening of the essential oil against nine pathogenic organisms obtained via due process from University College Hospital, Ibadan, Nigeria. Data were statistically analysed. 20 compounds representing 94.7% of the essential oil were characterised. The most abundant component of the oil was 1,10-di-epi-cubenol (30.0%); an oxygenated sesquiterpene and 5 out of the 20 components had less than 1.0 % concentration of compound viz. nonanal (0.7%), cis-α-ambrinol (0.9%), calamenene 10,11-epoxide (0.5%), α-calacorene (0.7%) and n-hexadecane (0.8%). At 106 cfu/ml, inoculum concentration of organism, the essential oil exhibited significant antimicrobial activity against 6 out of the 9 organisms. The F-value for the antimicrobial assay was significant for the model and organisms. The oil showed remarkable antimicrobial activity against Salmonella typhi (47.50 mm), Candida albicans (41.00 mm), Escherichia coli (39.00 mm), Klebsiella pneumoniae (31.50 mm), Pseudomonas aeruginosa (31.00 mm) and Streptococcus pyogenes (30.00 mm). The bioactivity might be attributed to abundant sesquiterpenes component of the oil. Ethnobotanically, the essential oil could be the treatment of infections such as urinary tract infection, sore throat, typhoid fever and candidiasis. However, toxicological study of the oil will confirm its safety in administration.
Keywords Cleome viscosa, volatile oil, terpenes, 1,10-di-epi-cubenol, infections, herbal medicine.