In vitro antimicrobial synergism within plant extract combinations from three South African medicinal bulbs

Ethnopharmacological relevance: Tulbaghia violacea, Hypoxis hemerocallidea and Merwilla plumbea are used in South African traditional medicine for the treatment of some infectious diseases and other ailments. Aim of the study: The study aimed at investigating the antimicrobial efficacies of independent and various within-plant extract combinations of three medicinal bulbs to understand the possible pharmacological interactions. Materials and methods: Bulb and leaf extracts of the three medicinal plants, independently and in combinations, were comparatively assessed for antimicrobial activity against two Gram-positive and two Gram-negative bacteria and Candida albicans using the microdilution method. The fractional inhibitory concentration indices (FIC) for two extract combinations were determined. Results: At least one extract combination in each plant sample demonstrated good antimicrobial activity against all the test organisms. The efficacies of the various extract combinations in each plant sample varied, with the strongest synergistic effect exhibited by the proportional extract yield combination of PE and DCM extracts in Merwilla plumbea bulb sample against Staphylococcus aureus (FIC index of 0.1). Most extract combinations demonstrated either a synergistic, additive or indifferent interaction effect against the test bacteria with only a few exhibiting antagonistic effects. Conclusion: The observed antimicrobial efficacy and synergistic interactions indicate the beneficial aspects of combination chemotherapy of medicinal plant extracts in the treatment of infectious diseases. (C) 2011 Elsevier Ireland Ltd. All rights reserved.