Antimicrobial activity of the volaite oils of plectranthus Kilimandcharica ( labiatae) and polygala sphenoptera (polygalaceae).

Two plants Plectranthus kilimandscharica Guerke (Labiatae) and Polygala sphenoptera Fresen (Polygalacese) were selected for study based on their ethnomedical use in the treatment of infections. Essential oils from the two plants were obtained by hydro-distillation, using a Clavenger-type apparatus. The yield of oil from the fresh leaves of Plectranthus kilimandscharica was 0.12% v/w and that from the dried aerial parts of Polygala sphenoptera was 1% v/w. The oils were subjected to antimicrobial tests against Gram positive bacteria, i.e. Staphylococcus aureus, and Streptococcus pyogenes, Gram negative bacteria, i.e. Escherichia coli, Pseudomonas aeruginosa and Shigella flexineri; and a yeast Candida albicans. The tests were carried out at various concentrations of the oils by the Broth Dilution method, using nutrient broth as the growth medium. Of all the bacteria tested, S. flexineri and Staph. aureus were found to be the most sensitive to the essential oil obtained from Polygala sphenoptera, while E, coli was the most sensitive to Plectranthus kilimandscharica oil. Staphylococcus aureus was of intermediate sensitivity to the latter oil; Pseudomonas aeruginosa showed intermediate sensitivity to the oil from Polygala sphenoptera; but was resistant to that from Plectranthus kilimandscharica. Streptococcus pyogenes and Candida albicans were resistant to oils from both plants. Shigella flexineri showed intermediate sensitivity to the oil from Plectranthus kilimandscharica. This study has shown that the essential oils from the two plants have antimicrobial effect. However, the antimicrobial effect is not very promising. Generally, Polygala sphenoptera oil showed greater antimicrobial potential than Plectranthus kilimandscharica on the microorganisms used in this study