Abstract
Terminalia laxiflora, Terminalia brownii and Anogeissus leiocarpus are used as decoctions, macerations, infusions and fumigations in East and West African traditional medicine for treatment of infectious diseases and their symptoms. Using this ethnopharmacological information as a guideline for our research and owing to the fact that these species have not been subjected to in depth antibacterial and phytochemical studies, thirty-nine extracts of various polarities of the stem bark, stem wood and roots were studied for growth inhibitory effects against the human pathogenic bacteria Staphylococcus epidermidis, Staphylococcus aureus, Micrococcus luteus and Pseudomonas aeruginosa. Our results indicate that the studied species contain antibacterial compounds of a wide range of polarities. All polar root extracts of T. laxiflora and various polar extracts of T. brownii roots, including hot water decoctions, gave broad-spectrum antibacterial effects and low MIC values of 39μg/ml. The main ellagitannins in an ethyl acetate extract of the root of T. laxiflora were found to be corilagin and its derivative and punicalagin. A methanol extract of the roots of T. brownii contained methyl-(S)-flavogallonate and its derivative as the main identified ellagitannins. Moreover, both Terminalia species were found to contain ellagic acid xylopyranoside and methyl ellagic acid xyloside and pure ellagic acid was present in T. brownii. Pure punicalagin did not give as low MIC as an ethyl acetate extract of the roots of T. laxiflora, containing punicalagin as one of its main compounds, although this ellagitannin totally inhibited the growth of S. aureus at 125μg/ml and P. aeruginosa at 500μg/ml. Similarly, pure ellagic and gallic acid gave higher MIC values than the methanolic root extract of T. brownii against S. aureus and P. aeruginosa. Moreover, a Sephadex LH-20 fraction of the methanolic extract of the roots of T. brownii, enriched with methyl-(S)-flavogallonate and its isomer, gave higher MIC values than the crude methanolic extract. These results suggest that the polyphenols in the extracts might act synergistically with each other. A methanolic soxhlet extract of the roots of A. leiocarpus, containing ampelopsin, aromadendrin, taxifolin, pinosylvin and 4′-methylpinosylvin gave a low MIC value of 39μg/ml against all bacterial strains used in this investigation. Our results demonstrate that the roots, stem bark and stem wood of T. brownii, T. laxiflora and A. leiocarpus are rich sources of (new) antimicrobial compounds and justify the uses of these plants for treatment of infections in African traditional medicine.
Highlights
Bacterial infections such as acute respiratory disorders and diarrhoea are still the number one cause of death among children aged under five in Sub-Saharan Africa (Mulholland and Adegbola, 2005) and in most developing countries globally (WHO, 2003)
Antibacterial results Thirty-nine extracts of various polarities, including decoctions of the roots, stem bark and stem wood of the traditional medicinal plant species Terminalia laxiflora, T. brownii and Anogeissus leiocarpus were screened for their antibacterial effects (Table 2 and 3)
The plant species were chosen according to their reported uses for treatment of bacterial infections in African traditional medicine (Table 1) and due to the fact that these species only to a limited extent have been investigated for their antimicrobial effects and compounds especially when it comes to the root part
Summary
Bacterial infections such as acute respiratory disorders and diarrhoea are still the number one cause of death among children aged under five in Sub-Saharan Africa (Mulholland and Adegbola, 2005) and in most developing countries globally (WHO, 2003). Antibiotic resistance has become a growing problem in Africa as in the rest of the world (Spencer, 2007). In the developing world, including Africa, few suitable and affordable conventional antibiotic therapies are available (WHO, 2003). Africa is a rich source of medicinal plants and depending on the country an estimated 60-80 % of the populations are using plants as readily available and affordable phytomedicines (Apulu et al, 1994; Mahomoodally, 2013; Schmelzer and Gurib-Fakim, 2013). New antimicrobial compounds with new mechanisms of actions could be found from these phytomedicines and from plant species based on their ethnomedical use for treatment of infections (Cos et al, 2006)
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