Abstract
New measures to control infections in humans and other animals are continuously being sought because of the increasing resistance of bacteria to antibiotics. In a wide tree screening survey of the antimicrobial activity of extracts of tree leaves (www.up.ac.za/phyto), Ochna pulchra, a small tree found widely in southern Africa, had good antibacterial activity. We therefore investigated the antibacterial activity of acetone leaf extracts of some other available Ochna spp. Antibacterial activity and the number of antibacterial compounds in acetone leaf extracts of Ochna natalitia, Ochna pretoriensis, O. pulchra, Ochna gamostigmata and Ochna serullata were determined with a tetrazolium violet serial microplate dilution assay and bioautography against Staphylococcus aureus, Escherichia coli, Enterococcus faecalis and Pseudomonas aeruginosa, bacteria commonly associated with nosocomial infections. The percentage yields of the extracts varied from 2.5% to 8%. The minimum inhibitory concentrations of the five species ranged from 40 µg/mL to 1250 µg/mL. E. coli was sensitive to all the extracts. The O. pretoriensis extract was the most active with minimum inhibitory concentrations of 0.065 mg/mL and 0.039 mg/mL against E. coli and E. faecalis, respectively. The O. pretoriensis extract also had the highest total activities of 923 mL/g and 1538 mL/g, indicating that the acetone extract from 1 g of dried plant material could be diluted to 923 mL or 1538 mL and would still kill these bacteria. Based on the bioautography results, the two most active species, O. pretoriensis and O. pulchra, contained at least 10 antibacterial compounds with similar R f values. Some of these antibacterial compounds were polar and others were non-polar. Variation in the chemical composition of the species may have some taxonomic value. The order of activity of the species to the bacteria were O. pretoriensis > O. pulchra > O. gamostigmata > O. serullata > O. natalitia. Even before toxicity and bioavailability issues are considered, some Ochna spp. leaf extracts have the potential to be used in treating skin infections.
Highlights
Medicinal plants which form the backbone of traditional medicines have in the last few decades been subjected to many pharmacological studies
We have found that plants used traditionally to treat infections have very low antibacterial activity in in vitro assays
The good activity of O. pretoriensis motivated the present investigation of the antibacterial activity and the number of antibacterial compounds present in other, available Ochna species: Ochna natalitia, O. pretoriensis, O. pulchra, Ochna gamostigmata and Ochna serullata
Summary
Medicinal plants which form the backbone of traditional medicines have in the last few decades been subjected to many pharmacological studies. The genus Ochna comprises about 86 species of evergreen shrubs belonging to the family Ochnaceae and occurs widely in Africa, Asia and Madagascar. This family of plants has been used as food and for medicinal purposes for many centuries. The study involved the isolation of biflavonoids with antimalarial activity; a flavonoid glycoside with anti HIV-1 activity was isolated from the same species.[9] An infusion of the roots and leaves of O. integerrima is used locally as an antidysenteric and antipyretic preparation.[10] There appears to be no previous report on the antibacterial activity of any of the 86 species of Ochna to date. The good activity of O. pretoriensis motivated the present investigation of the antibacterial activity and the number of antibacterial compounds present in other, available Ochna species: Ochna natalitia, O. pretoriensis, O. pulchra, Ochna gamostigmata and Ochna serullata
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