Abstract

Interest in plants’ essential oils has grown recently due to increased use of natural products in medicine and cosmetics. In spite of its long use, there has been little prior study on the bioactivity and toxicity of the essential oils of Crassocephalum crepidioides (Benth S. More). Thus in this work, the anti-bacterial and brine shrimps’ lethality of the essential oils obtained through hydro-distillation were evaluated. The oils were analyzed by gas chromatography and gas chromatography/mass spectrometric techniques. The toxicity of the oils was considered using the brine shrimps’ lethality assay at concentrations of 10, 100 and 1000 ppm. The antimicrobial assay was carried out using the agar diffusion method. The bacteria were three strains of Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis and Salmonella Typhi) and two strains of Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa). The main constituents of the leaves essential oil of C. crepidioides were α-caryophyllene (10.29%) and β-cubebene (13.77%), while the stem essential oil were mainly thymol (43.93%) and 4-cyclohexybutyramide (20.94%). The results of the brine shrimps’ lethality assay suggest that the essential oil of the stem (LC₅₀ = 9.10 µg/mL) was just as toxic as the essential oil of the leaves (LC₅₀ = 9.2 µg/mL). The essential oils were active against all the bacterial strains but low when compared with the standard antibiotic, Gentamicin.

Key words: Essential oils, toxicity, antibacterial activity, Crassocephalum crepidioides, Nigeria.