RESUMO
ETHNOPHARMACOLOGICAL RELEVANCE: Plants are often combined in traditional herbal remedies to increase medicinal efficacy, thus this investigation provides some insight into the antimicrobial efficacies of selected combinations. AIMS OF THE STUDY: The first aim was to scientifically validate antibacterial efficacy of plant mixtures that are traded within peri-urban centres of Cape Town (Western Cape, South Africa). This was followed by an in-depth evaluation of the most antimicrobially active mixture; Agathosma crenulata, Dodonaea viscosa with Eucalyptus globulus. MATERIALS AND METHODS: Methanol and aqueous extracts of six plant mixtures were screened for antibacterial properties against two Gram-negative and two Gram-positive bacteria using the minimum inhibitory microdilution method. Thereafter, chloroform: methanol (1:1; v/v) extracts, essential oils and aqueous extracts of Agathosma crenulata, Dodonaea viscosa and Eucalyptus globulus were assayed for antimicrobial activity independently and in various combinations. The fractional inhibitory concentration indices (Æ©FIC) were determined for double and triple plant combinations to establish antimicrobial interactions. RESULTS: From the six plant mixtures prepared by herbalists, a methanol extract derived from combining Agathosma crenulata, Dodonaea viscosa and Eucalyptus globulus showed the best antibacterial activity. The MIC values of 49µg/ml for Staphylococcus aureus and Bacillus subtilis, and 98µg/ml for Klebsiella pneumoniae and Escherichia coli were recorded. When Agathosma crenulata, Dodonaea viscosa and Eucalyptus globulus were mixed in various 1:1 combinations, mostly additive and synergistic interactions were noted. The most noteworthy synergistic (ΣFIC value 0.07) 1:1 combinations were observed for the chloroform: methanol extracts of Agathosma crenulata mixed with Eucalyptus globulus against Klebsiella pneumoniae, Staphylococcus aureus and Bacillus subtilis. When combined in a mixture of three plants (1:1:1), enhanced efficacy was evident against most of the pathogens, for both organic and aqueous extracts. The triple combination against Bacillus subtilis demonstrated the greatest synergy (ΣFIC values of 0.03). CONCLUSIONS: The enhanced antimicrobial efficacy and synergistic interactions noted for some of the mixtures, particularly the combination of Agathosma crenulata, Dodonaea viscosa and Eucalyptus globulus support the Western Cape Khoi-San traditional medicinal practices of combining plants for enhanced efficacy.
