European Journal of Medicinal Plants

The problem of microbial resistance is growing and the outlook for the success of antimicrobial drugs in the future is still uncertain. For a long period, plants have been a valuable source of natural products for maintaining human health, thus, such plants should be investigated to better understand their antimicrobial properties, safety and efficacy. This study evaluated, in vitro, antimicrobial activities of aqueous and ethanol fractions of six selected medicinal plants: Eugenia caryophyllata, Psidium guajava, Alchornea cordifolia, Cinnamomum zeylanicum, Zanthoxylum xanthoxyloides (Fagara), and Tridax procumbens against nineteen (19) clinical isolates and a standard strain of Staphylococcus aureus, using a modified agar diffusion method. The potencies of sixteen (16) formulations from five of the medicinal plants that individually showed significant antimicrobial activity were also evaluated. The ethanol fractions of the six medicinal plants inhibited the growth of all the test organisms with zones of inhibition ranging from 12.0-16.0 mm (averaging 13.3 mm) whereas that of the aqueous fractions of the six medicinal plants ranged from 6.0-18.0 mm (averaging 10.9 mm). Formulations which include Alchornea cordifolia and Eugenia cryophyllata showed inhibition zones ranging from 7.0-16.0 mm. There was significant difference between the ethanol and aqueous plant extracts against S. aureus used in this study. Minimum inhibition concentrations (MICs) of the herbal preparations used against the control strain (Staphylococcus aureus ATCC^® 29213^™) and the clinical S. aureus isolates showed that both the aqueous and ethanol extracts of Alchornea cordifolia and the ethanol extract of Cinnamomum zeylanicum produced the lowest MICs of 2 mg/ml. The results, therefore, show that these plants possess antibacterial activities that could be further investigated to identify the compound(s) responsible for the antibacterial activities.