Fifty-one essential oils extracted from plants of known origin were tested for their antimicrobial activity against three bacteria, Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli and four yeasts, Torulopsis utilis, Schizosaccharomyces pombe, Candida albicans and Sacccharomyces cerevisiae using the drop diffusion method. All showed antimicrobial activity against at least one of the micro-organisms. Following this preliminary screening, 13 essential oils showing anti-microbial activity against at least five of the micro-organisms were tested in the range 50ug ml-1 to 500ug ml-1 using broth micro dilution techniques with dimethylsulphoxide (DMSO) as a dispersing solvent. The concentration of most of the oils required for total inhibition of growth was >500ug ml-1. Further studies on the antimicrobial action of cinnamon oil in the range 10-150ug ml-1 showed that 50-fold higher activity was found when no dispersing solvent was used.
