In Vitro Antimicrobial Synergism of Three Indian Medicinal Plant Extracts Alone and in Combination With Different Antimicrobials Against Pathogenic Bacterial Strains

Abstract

Aim: To evaluate the antimicrobial efficacies of independent and various within plant extract combinations of three medicinal plants. The fruits, roots and whole plant of the three medicinal plants viz Phyllanthus niruri, Bergenia ligulata and Tribulus terrestris independently and in combination were comparatively assessed for antimicrobial activity against Gram+ve i.e. Staphylococcus aureus (MTCC 96), Bacillus subtilis (MTCC 121) and Enterococcus faecalis (NCIM 5025) and Gram-ve i.e. Enterobacter aerogenes (MTCC 111), Klebsiella pneumonia (MTCC 109), Salmonella typhimurium (MTCC 98), Shigella dysenteriae (clinical strain) and Escherichia coli (MTCC 46). Methods: The interaction between plant extracts and antimicrobial agents was carried out using disc diffusion method and broth dilution methods were used to determine the minimum inhibitory concentration (MIC) of the bacterial strains. Results: The results showed good antibacterial activity against all tested organisms. The efficacies of various extract combinations of each plant sample varied, with the strongest synergistic effect was exhibited by the proportional extract herbal combination of Phyllanthus niruri, Bergenia ligulata and Tribulus terrestris against E.Coli. Most combinations demonstrated either a synergistic or indifferent interaction effect against test bacteria with few exhibiting antagonistic effects. The diameter of the zones of inhibition of the extract combinations ranged from 6.0±0.5 to 32.3±0.8. The minimum inhibitory concentration (MIC) of different extracts ranged from 0.78 mg/mL to 25mg/mL. Conclusion: These results indicate better synergistic effect with polyherbal combination rather than a single plant which can enhance the antibacterial potential and hence can be useful in fighting emerging drug resistance microorganisms.