Abstract

Extracts obtained from 10 trees used in South African traditional medicine were screened for antibacterial, anti-inflammatory (COX-1 and COX-2) and anti-cholinesterase activities and investigated for potential mutagenic effects using the Ames test. Antibacterial activity was detected using the disc-diffusion and micro-dilution assays. The extracts were tested against Gram-positive bacteria: Bacillus subtilis, Staphylococcus aureus, Micrococcus luteus and Gram-negative bacteria: Escherichia coli and Klebsiella pneumoniae. Of the 78 different plant extracts investigated, 80% showed activity against both Gram-positive and Gram-negative bacteria in the disc-diffusion assay. In the micro-dilution assay, 60% of the plant extracts showed minimum inhibitory concentration (MIC) values ≤1.56 mg ml⁻¹. The lowest MIC value (0.092 mg ml⁻¹) was recorded for an ethyl acetate root extract of Acacia sieberiana against Staphylococcus aureus and Escherichia coli. In the anti-inflammatory assay, 70% of the investigated plant extracts (0.25 mg ml⁻¹) inhibited both COX-1 and COX-2 activity (>50% and 70% for water and organic solvent extracts, respectively). An ethyl acetate leaf extract of Trichilia dregeana showed selective inhibition of COX-2 (81%). In the acetylcholinesterase inhibitory test, 21% of the plant extracts were active at a concentration ≤1 mg ml⁻¹ using the micro-dilution assay. The lowest IC₅₀ value was 0.04 mg ml⁻¹ obtained with an ethanol bark extract of Combretum kraussii. None of the investigated plants showed any potential mutagenic effects.

Keywords: Antibacterial activity; Anti-inflammatory activity; Acetylcholinesterase inhibitory activity; Genotoxicity

Abbreviations: AChE, acetylcholinesterase; ATCI, acetylthiocholine iodide; BSA, bovine serum albumin; DTNB, 5,5-dithiobis-2-nitrobenzoic acid; INT, iodonitrotetrazolium violet; MH, Mueller–Hinton agar; MIC, minimum inhibitory concentration; TLC, thin layer chromatography

Article Outline

1. Introduction

2. Materials and methods

2.1. Plant material

2.2. Disc-diffusion assay

2.3. Micro-dilution antibacterial assay

2.4. Cyclooxygenase assays

2.5. Acetylcholinesterase enzyme inhibitory activity

2.6. Genotoxicity test

3. Results

3.1. Antibacterial activity

3.2. Cyclooxygenase activity

3.3. Acetylcholinesterase enzyme inhibitory activity

3.4. Ames genotoxicity assay

4. Discussion and conclusions

Acknowledgements

References