Screening of medicinal plants for antibacterial activity

Plant-derived compounds have long been playing a crucial role in drug discovery and development, representing a potential source of new anti-infective agents. It was supposed that the antimicrobial compounds from plants may inhibit bacteria through different mechanisms than conventional antibiotics, and could therefore be of clinical value in the treatment of resistant microbial strains [1]. Herein, we report the evaluation of antibacterial activity of fourteen medicinal plants, which were collected in Mozambique. Seventy crude extracts were obtained by both successive extraction methods and by decoction according to traditional use. Four organic solvents with varying polarity (n-hexane, dichloromethane, ethylacetate, and 70% ethanol) were used for the extraction. The extracts were tested against two Gram-positive strains: Staphylococcus aureus ATCC 25923, Enterococcus faecalis ATCC 51299, and four Gram-negative strains: Klebsiella pneumoniae ATCC 9997, Klebsiella pneumoniae ID 2564, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 27853 by broth dilution method. Eight plants extracts showed moderate to significant activity against Gram-positive strains. The n-hexane and dichloromethane extracts of Anacardium occidentale L. showed highest inhibition against E. faecalis ATCC 51299 (MIC=31µg/mL), and the 70% EtOH extract of Adansonia digitata L. exhibited activity to S. aureus ATCC 25923 (MIC=62µg/mL). However, no extract showed activity to Gram-negative bacteria with concentrations ranging from 0.9µg/mL to 500µg/mL.

Acknowledgements: This study was supported by a fellowship from FCT, Portugal (reference number SFRH/BPD/37179/2007).

References: 1. Eloff, J.N. et al. (1998)J. Ethnopharm. 60:1–8.