Southern African Medicinal Plants Research Articles

Antimicrobial activity of Southern African medicinal plants on Helicobacter pylori and Lactobacillus species

Ethnopharmacological relevanceNumerous medicinal plants have been used traditionally in South Africa for gastric ulcer treatment. Helicobacter pylori is known for causing inflammation and the onset of gastric ulcers. While several studies explored medicinal plants against H. pylori, investigation of medicinal plants used for gastric ulcers has been neglected, as well as the effects these plants would have on bacteria occurring naturally in the gut microbiome. Aim of the studyThis study aimed to investigate Southern African medicinal plants used traditionally for treating gastric ulcers against H. pylori , as well as the effects that these plants have when combined with Lactobacillus species and tested against H. pylori. MethodologyBased on evidence from the ethnobotanical literature, 21 plants were collected. Their antimicrobial activity was assessed against five clinical H. pylori strains, and in combination with each of three Lactobacillus species, using the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) broth microdilution assays. Toxicity was assessed using the brine shrimp lethality assay. ResultsNoteworthy activity was observed against at least one H. pylori strain for 12 plant species. The lowest mean MICs were from organic extracts of Carissa edulis Vahl (0.18 mg/mL) and Chironia baccifera L. (0.20 mg/mL), and aqueous extracts of Sansevieria hyacinthoides (L.) Druce (0.26 mg/mL) and Dodonaea viscosa Jacq. (0.30 mg/mL). Aqueous extracts of the investigated plants were combined with Lactobacillus species, and the majority of combinations showed increased antimicrobial activity compared with the extracts alone. Combinations of Lactobacillus rhamnosus with 18 of the 21 aqueous plant extracts showed at least a two-fold decrease in the mean MBC against all H. pylori strains tested. Lactobacillus acidophilus combined with either Protea repens L., Carpobrotus edulis (L.) L. Bolus or Warburgia salutaris (Bertol.f.) Chiov. aqueous extracts had the best anti-H. pylori activity (mean MBCs of 0.10 mg/mL for each combination). Only four organic and one aqueous extract(s) were considered toxic. ConclusionThese results highlight the potential of medicinal plants to inhibit H. pylori growth and their role in traditional treatments for the management of ulcers. The results also indicate that aqueous extracts of these plants do not hinder the growth of bacteria that occur naturally in the gut microbiome and play a role in maintaining gut health, as well as show the potential benefit of including Lactobacillus species as potentiators of H. pylori activity.

Leaf extracts of eight selected southern African medicinal plants modulate pro-inflammatory cytokine secretion in LPS-stimulated RAW 264.7 macrophages

This study investigates the anti-inflammatory properties of extracts prepared from the leaves of eight southern African medicinal plants used traditionally to treat inflammation and pain. The inhibitory effect of aqueous and ethanol extracts on the release of pro-inflammatory cytokines was determined in lipopolysaccharide (LPS) stimulated and unstimulated RAW 264.7 murine macrophage cells. The levels of interleukin (IL)-1β, IL-6, tumour necrosis factor-α (TNF-α), interferon-gamma (IFN-γ), monocyte chemoattractant protein 1 (MCP-1) and macrophage inflammatory protein (MIP)-2 release were determined using cytokine multiplex-bead assays. The ethanol extracts of Melianthus comosus Vahl (commonly known as honey flower), Tetradenia riparia (Hochst.) Codd (misty plume bush) and Warburgia salutaris (G. Bertol.) Chiov. (pepper-bark tree), demonstrated the most significant inhibitory activity, with over 50-fold inhibition of IL-1β, IL-6 and TNF-α levels in LPS-stimulated RAW 264.7 macrophages. The aqueous extract of M. comosus also significantly inhibited the secretion of all the tested cytokines and chemokines. Phytochemical investigation of M. comosus ethanol leaf extract using ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry (UHPLC-HRMS) led to the detection of crassolide, deoxylimonoic acid D-ring-lactone, 2-hydroxynonanoic acid and 5-noniloxytryptamine. To the best of our knowledge, the cytokine inhibition properties of most of the medicinal plants screened in this study are reported for the first time. Our results support the use of southern African medicinal plants as anti-inflammatory remedies and provide an insight into the immunomodulatory mechanisms of action.

An imprecise probability approach-based determination of over-represented southern African plant genera and families used in ethnopharmacology

Ethnopharmacological relevanceThe analyses of patterns of over-representation of southern African traditional medicinal plants at the genus and family level provide information about the differences in plant use among southern African countries and disease categories. ‘Over-representation’ refers to the phenomenon whereby the proportion of plants belonging to a taxonomic group is higher in ethnobotanical pharmacopoeia than in the total flora. Aim of the studyThis study aimed to use the Imprecise Dirichlet Model (IDM) to analyse data from ten southern African countries to establish how over-represented medicinal plant families compare with over-represented genera, how over-represented medicinal taxa differ among countries in this region of Africa, and how over-represented taxa differ among six major disease categories. Materials and methodsFloral data for the total species composition of each country were obtained from online databases. Medicinal plant species lists were generated from published surveys, inventories, and books. IDM calculations were executed using the inverse of the cumulative beta probability density function in Microsoft Excel™. Python programming language source code was used to calculate Pearson correlation (r) values and Jaccard coefficients (J). ResultsNine of forty-two over-represented medicinal plant families in southern Africa (group 1) do not have over-represented genera. Seven of the forty genera with the highest margins of over-representation belong to under-represented families. Nineteen of the forty-two over-represented families have margins of over-representation smaller than the cumulative margins of their over-represented genera. Groups of countries with similar overall flora (J ≥ 0.333) are Botswana and Namibia (group 2), Malawi, Mozambique, Zambia and Zimbabwe (group 3). The families and genera with the highest margins of over-representation are Loganiaceae and Albizia in group 1, Combretaceae and Vachellia in group 2, Dioscoreaceae and Senna in group 3, and Sapotaceae and Solanum in group 4 (South Africa). The families and genera with the highest margins of over-representation across disease categories are Ebenaceae and Albizia, Canellaceae and Dicoma, Combretaceae and Pterocelastrus, Ebenaceae and Bersama, Francoaceae and Erythrina, and Aristolochiaceae and Strychnos for plants used in the treatment of STIs, febrile and mosquito-vector diseases, microbial infections, pain, skin conditions, and female sexual/reproductive problems, respectively. ConclusionsGenus-level calculations are more efficient in generating taxonomic lists that can be used for ethnopharmacological investigations due to the exclusion of under-represented genera. Limiting the size of geographical areas from which medicinal plant lists are sampled and targeting plants used to treat specific types of disease prevents the underestimation of niche over-represented taxa.

Inhibition of pro-inflammatory cytokines by selected southern African medicinal plants in LPS-stimulated RAW 264.7 macrophages

Ethnopharmacological relevanceBark is frequently used in southern African traditional medicine to treat inflammation, yet it remains to be rigorously examined for its immunological and anti-inflammatory activity. Aim of the studyBarks obtained from ten important and popular southern Africa plants were evaluated for their anti-inflammatory and immunomodulatory properties against the secretion of some pro-inflammatory cytokines (interleukin (IL)-1β, IL-6, tumour necrosis factor-α (TNF-α), and interferon-gamma (IFN-γ) as well as chemokines (monocyte chemoattractant protein 1 (MCP-1) and macrophage inflammatory protein (MIP)-2) in murine RAW 264.7 macrophages. Materials and methodsThe inhibitory effects of aqueous and ethanol extracts were determined using cytokine multiplex-bead assays in lipopolysaccharide (LPS)-stimulated and unstimulated RAW 264.7 cells. ResultsOverall, the ethanol extracts were more potent cytokine inhibitors compared to the aqueous extracts. The LPS-stimulated cells treated with the ethanol extracts of Erythrina lysistemon Hutch., Pterocelastrus rostratus Walp. Syzygium cordatum Hochst. ex Krauss and Warburgia salutaris (G. Bertol.) Chiov., demonstrated significant (p < 0.005) inhibition up to 85% of IL-1β, IL-6, and TNF-α secretion compared to the LPS control. Additionally, P. rostratus and S. cordatum aqueous bark extracts substantially decreased the secretion of all the tested cytokines and chemokines. Chemical investigation of the S. cordatum extract resulted in the identification of four ellagic acid derivatives: ellagic acid 4-O-α-rhamnopyranoside (1), ellagic acid 4-O-α-4″-acetylrhamnopyranoside (2), 3-O-methylellagic acid 4′-O-α-3″-O-acetylrhamnopyranoside (3) and 3-O-methylellagic acid 4′-O-α-4″-O-acetylrhamnopyranoside (4), along with mixtures of ellagic acid 4-O-α-2″-acetylrhamnopyranoside (5), ellagic acid 4-O-α-3″-acetylrhamnopyranoside (6) and ellagic acid (7). Their structures were confirmed by mass spectrometry, NMR spectroscopy, and comparison with data from literature. ConclusionThe cytokine inhibition properties of most of the medicinal plants screened herein are reported for the first time. Our results provide insights into the mechanism of action by which the selected southern African medicinal plants regulate inflammation.

Immunomodulatory and cytotoxicity properties of selected southern African medicinal plants traditionally used to treat pain and inflammation

The use of medicinal plants to treat inflammatory and auto-immune disorders is a common practice in southern African. However, the mechanisms of action related to the traditional use of herbal remedies as immunomodulatory agents remain relatively unknown. This study aims to investigate the cytotoxic and immunomodulatory properties of important southern African medicinal plants used traditionally to treat inflammation and pain. Cytokine multiplex-bead assays were used to evaluate the anti-inflammatory effects of seventeen medicinal plants against interleukin-2 (IL-2) and interleukin-10 (IL-10) activity. The assay was conducted using lipopolysaccharide (LPS)-stimulated and unstimulated murine RAW 264.7 macrophage cells treated with aqueous and ethanol extracts. The MTS assay was used to determine the percentage cell viability and 50% cytotoxic concentration (IC50) in RAW 264.7 and human dermal fibroblast (HDF) cell lines. The aqueous extracts showed minimal cytotoxicity at the highest concentration screened (5mg/mL). Unstimulated RAW 264.7 cells treated with the plant extracts exhibited immunomodulatory effects by significantly up-regulating the production of an anti-inflammatory cytokine IL-10 compared to the LPS-stimulated extracts. The aqueous bark extract of Erythrina lysistemon Hutch., as well as the leaves of Warburgia salutaris (G. Bertol.) Chiov., and Zantedeschia albomaculata (Hook.) Baill showed the greatest stimulation of IL-10 and IL-2 production in RAW 264.7 cells. Of note, E. lysistemon showed exceptional results by regulation the levels of IL-10 up to 7000-fold increase compared to the negative LPS unstimulated control. This study provides insights to the possible mechanisms involved in the use of southern African medicinal plants as immunomodulatory agents.

The traditional use of southern African medicinal plants to treat oral pathogens, and studies into their relevant antimicrobial properties

The traditional use of southern African medicinal plants to treat oral pathogens, and studies into their relevant antimicrobial properties

A Review of the Green Synthesis of ZnO Nanoparticles Utilising Southern African Indigenous Medicinal Plants.

Metal oxide nanoparticles (NPs), such as zinc oxide (ZnO), have been researched extensively for applications in biotechnology, photovoltaics, photocatalysis, sensors, cosmetics, and pharmaceuticals due to their unique properties at the nanoscale. ZnO NPs have been fabricated using conventional physical and chemical processes, but these techniques are limited due to the use of hazardous chemicals that are bad for the environment and high energy consumption. Plant-mediated synthesis of ZnO NPs has piqued the interest of researchers owing to secondary metabolites found in plants that can reduce Zn precursors and stabilise ZnO NPs. Thus, plant-mediated synthesis of ZnO NPs has become one of the alternative green synthesis routes for the fabrication of ZnO NPs. This is attributable to its environmental friendliness, simplicity, and the potential for industrial-scale expansion. Southern Africa is home to a large and diverse indigenous medicinal plant population. However, the use of these indigenous medicinal plants for the preparation of ZnO NPs is understudied. This review looks at the indigenous medicinal plants of southern Africa that have been used to synthesise ZnO NPs for a variety of applications. In conclusion, there is a need for more exploration of southern African indigenous plants for green synthesis of ZnO NPs.

Review: Southern African medicinal plants used as blood purifiers.

Blood purification practices, also referred to as blood cleansing or detoxification, is an ancient concept which is widespread amongst African traditional medicine, but for which no modern scientific basis exists. There prevails considerable ambiguity in defining what a blood purifier is. The purpose of this review is to firstly define what a blood purifier is in the context of African traditional medicine and compare to other cultural and westernized interpretations. Thereafter, this study identifies traditionally used medicinal plants used as blood purifiers in southern Africa and correlates these species to scientific studies, which may support evidence for these "blood purifying plant species". Ethnobotanical books and review articles were used to identify medicinal plants used for blood purification. Databases such as Scopus, ScienceDirect, PubMed and Google Scholar were used to source scientific articles. An evaluation was made to try correlate traditional use to scientific value of the plant species. One hundred and fifty nine plant species have been documented as traditional remedies for blood purification. Most of the plant species have some pharmacological activity, however, very little link to the traditional use for blood purification. There has been some justification of the link between blood purification and the use as an antimicrobial and this has been explored in many of the plant species identified as blood purifiers. Other pharmacological studies specifically pertaining to the blood require further attention. Irrespective of the ambiguity of interpretation, medicinal plants used to "cleanse the blood", play an important holistic role in traditional medicine and this review with recommendations for further study provides some value of exploring this theme in the future.

Antimicrobial activity and toxicity profile of selected southern African medicinal plants against neglected gut pathogens

Anaerobes outnumber aerobic bacteria in the human gut. The most commonly isolated microorganisms in intra-abdominal infections include Escherichia coli, Peptostreptococcus micros as well as Bacteroides and Clostridium species. Several studies have been undertaken on southern African medicinal plant species and their antimicrobial efficacy against pathogens such as E. coli that cause stomach ailments. However, pathogens such as Helicobacter pylori, Fusobacterium varium as well as others have been neglected in medicinal plant antimicrobial research. The aim of this study was to evaluate the antimicrobial activity of selected medicinal plants documented for stomach ailments against neglected gut pathogens. A total of 102 aqueous and organic extracts were prepared from 40 different plant species. These plant samples were screened for antimicrobial efficacy against eight anaerobes and two microaerophilic strains using the micro-dilution antimicrobial assay. Plant extracts that displayed noteworthy antimicrobial activity against Clostridium perfringens were further evaluated for antibiofilm activity using the crystal violet staining assay. The toxicity profiles of plants that displayed noteworthy antimicrobial activity were evaluated using the brine shrimp lethality assay which revealed that most of the tested plant samples were non-toxic in nature, and the aqueous extracts proved to be safer. The organic extract of Lippia javanica leaf showed the best antimicrobial activity with a minimum inhibitory concentration of 0.5 μg/mL against C. perfringens. The organic extract of Salvia africana-caerulea displayed the best antibiofilm activity overall, at cell attachment (4 h) biofilm developmental stage with inhibition percentages of 82.8%.&#x0D; Significance:&#x0D; &#x0D; L. javanica and Gunnera perpensa demonstrated the highest antimicrobial activity with minimum inhibitory concentrations of 0.5 μg/mL and 2.0 μg/mL against C. perfringens, respectively.&#x0D; Salvia africana-caerulea was the most effective plant species demonstrating biofilm attachment.&#x0D; Lowest toxic effects were observed for the organic extracts of Aloe marlothii, A. tenuior, Bridelia cathartica, G. perpensa leaf and the aqueous extracts of G. perpensa (leaf and rhizome).&#x0D; This study demonstrates, for the first time, both antimicrobial and antibiofilm activities for most of these plant species against neglected anaerobes.&#x0D; Noteworthy antimicrobial activities in many cases validate traditional use and safety.&#x0D;

Selected southern African medicinal plants with low cytotoxicity and good activity against bovine mastitis pathogens

Bovine mastitis, a disease caused by inflammation of the udder, is one of the major causes of global dairy industry losses. Alternative therapies such as ethnoveterinary medicine are worthy of further study since mastitis-causing bacterial pathogens are becoming increasingly resistant to conventional antibiotic therapy. Plant species were selected on the basis of their known antibacterial activity, use in ethnoveterinary medicine and their ready availability for in vitro testing against a panel of bacterial species implicated in causing mastitis (both ATCC strains and clinical isolates). Water and acetone extracts were prepared from various plant parts of Acacia nilotica, Tetradenia riparia, Aloe arborescens and Crassula multicava. Antimicrobial activity was determined using a serial microdilution assay and cytotoxicity was evaluated against a mammalian kidney cell line using a tetrazolium-based colorimetric assay.A. arborescens and C. multicava were not generally active against the tested bacteria. Acetone extracts of A. nilotica bark and T. riparia flower extracts were most active against Gram-positive bacteria. Activity against Gram-negative species, notably Proteus vulgaris and Enterobacter aerogenes, was also recorded with MIC values as low as 0.0195mg/ml. The best selectivity index (SI) value of 4.22 was obtained by the T. riparia flower acetone extract against the field strain of Streptococcus uberis. Although a degree of toxicity to mammalian cells was noted in most of the extracts, SI values above 1 indicate that antibacterial activity was greater than cellular toxicity for some extracts, a preliminary indication of safety. These extracts, or purified active compounds derived from them, may prove useful in further investigations of alternative mastitis treatments.

ChemInform Abstract: The Chemistry and Bioactivity of Southern African Flora II: Flavonoids, Quinones and Minor Compound Classes

AbstractReview: 134 refs + subrefs.

The chemistry and bioactivity of Southern African flora II: flavonoids, quinones and minor compound classes

This review is intended to highlight the relevance of natural products in drug discovery paying particular attention to those derived from Southern African medicinal plants with diverse biological activities.

Interactive antimicrobial and toxicity profiles of conventional antimicrobials with Southern African medicinal plants

Medicinal plant use plays an important role in the healthcare of many South Africans. Furthermore, in orthodox medicine, conventional antimicrobial agents are amongst the most commonly prescribed groups of drugs. Therefore, due to the prevalence of use of these two forms of healthcare, there is a high probability for their concurrent use. Thus, the aim of this study was to evaluate the interactive antimicrobial and toxicity profiles of six Southern African medicinal plants (Agathosma betulina, Aloe ferox, Artemisia afra, Lippia javanica, Pelargonium sidoides and Sutherlandia frutescens) when combined with seven conventional antimicrobials (ciprofloxacin, erythromycin, gentamicin, penicillin G, tetracycline, amphotericin B and nystatin). Antimicrobial activity was assessed using the minimum inhibitory concentration (MIC) assay against a range of pathogens and interactions were further classified using the sum of the fractional inhibitory concentration (∑FIC). Notable synergistic or antagonistic interactions were studied at various ratios (isobolograms). The toxicity of the individual samples, as well as the notable combinations, was assessed using the brine-shrimp lethality assay (BSLA) and the 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay on the HEK-293 human cell line. Of the 420 antimicrobial:plant combinations studied, 14.29% showed synergistic interactions, 7.56% antagonistic, 35.71% additive and 42.44% indifferent interactions. Some notable synergistic interactions (ciprofloxacin with A. betulina and S. frutescens against Escherichia coli) and antagonistic interactions (ciprofloxacin with A. afra organic extract against Escherichia coli) were identified. None of the notable combinations were found to show toxicity in the BSLA or MTT assay. In conclusion, the majority of combinations were found to have no notable interaction, alleviating some concern related to the concurrent use of these two forms of healthcare.

In vitro determination of the anti-aging potential of four southern African medicinal plants

BackgroundAging is an inevitable process for all living organisms. During this process reactive oxygen species generation is increased which leads to the activation of hyaluronidase, collagenase and elastase, which can further contribute to skin aging. Four southern African medicinal plants; Clerodendrum glabrum, Schotia brachypetala, Psychotria capensis and Peltophorum africanum, were investigated to assess their anti-aging properties.MethodsAnti-elastase, anti-collagenase and anti-hyaluronidase activities of twenty-eight samples, consisting of methanol and ethyl acetate extracts of the four plants, were determined using spectrophotometric methods. Radical scavenging activity was determined by the ability of the plant extracts to scavenge the ABTS•+ radical.ResultsThe majority of the samples in the anti-elastase assay and nine in the anti-collagenase assay showed more than 80% inhibition. The ethyl acetate extract of S. brachypetala bark and leaves of P. capensis inhibited elastase activity by more than 90%. The methanol extract of S. brachypetala bark contained the highest anti-hyaluronidase activity (75.13 ± 7.49%) whilst the ethyl acetate extract of P. africanum bark exhibited the highest antioxidant activity (IC50: 1.99 ± 0.23 μg/ml).ConclusionThe free radical scavenging activity and enzyme inhibitory activity of the plant extracts investigated suggests that they can help restore skin elasticity and thereby slow the wrinkling process. P. africanum was the plant with the most promising activity and will be subjected to further testing and isolation of the active compound/s.

Evaluation of the phenolic and flavonoid contents and radical scavenging activity of three southern African medicinal plants

Warburgia salutaris (Bertol. F.) Chiovs, Rhoicissus tridentata (L.f.) Wild & Drum andTerminalia sericea (Burch. ex DC.), are widely used medicinal plants in southern Africa. The aim of the study was to determine the phenolic and flavonoid content and evaluate the antioxidant activity of the three medicinal plants. Total phenolic and flavonoid contents were determined spectrophotometrically as gallic acid and rutin equivalents, respectively. Individual phenolic acids were identified by means of gas chromatography-mass spectrometry. Antioxidant activities of the crude extracts were assessed using the TEAC assay. The highest phenolic content was detected in the crude methanol extract of the bark of W. salutaris and the highest flavonoid content was found in the crude methanol extract of the leaves of this plant. In all the studied plants the alkaline hydrolysable fraction yielded a greater variety of phenolic acids compared to the soluble/free phenolic acid fractions. The three medicinal plants investigated were found to be strong radical scavengers supporting the traditional use of these medicinal plants. Key words: Antioxidant activity, flavonoids, medicinal plants, phenolic acids, phenolic content,Rhoicissus tridentata, Warburgia salutaris, Terminalia sericea.

Antimicrobial activity of southern African medicinal plants with dermatological relevance: From an ethnopharmacological screening approach, to combination studies and the isolation of a bioactive compound

Ethnopharmacological relevanceEthnobotanical reports on more than 100 southern African medicinal plants with dermatological relevance have been highlighted, yet there is still limited scientific data to support claims for their antimicrobial effectiveness against skin pathogens. Guided by ethnobotanical data, this paper explores the antimicrobial efficacies of southern African medicinal plants used to treat skin ailments. Aim of the studyTo investigate the antimicrobial properties of southern African medicinal plants against dermatologically relevant pathogens. The study also aimed at providing a scientific rationale for the traditional use of plant combinations to treat skin diseases and the isolation of the bio-active compound from the most active species, Aristea ecklonii (Iridaceae). Materials and methodsOrganic and aqueous extracts (132) were prepared from 47 plant species and screened for antimicrobial properties against dermatologically relevant pathogens using the micro-titre plate dilution method. Four different plant combinations were investigated for interactive properties and the sum of the fractional inhibitory concentration (ƩFIC) calculated. Isobolograms were used to further investigate the antimicrobial interactive properties of Pentanisia prunelloides combined with Elephantorrhiza elephantina at varied ratios. A bioactivity-guided fractionation process was adopted to fractionate the organic leaf extract of Aristea ecklonii. ResultsPlants demonstrating notable broad-spectrum activities (MIC values ≤1.00mg/ml) against the tested pathogens included extracts from Aristea ecklonii, Chenopodium ambrosioides, Diospyros mespiliformis, Elephantorrhiza elephantina, Eucalyptus camaldulensis, Gunnera perpensa, Harpephyllum caffrum, Hypericum perforatum, Melianthus comosus, Terminalia sericea and Warburgia salutaris. The organic extract of Elephantorrhiza elephantina, a plant reportedly used to treat acne vulgaris, demonstrated noteworthy antimicrobial activity (MIC value of 0.05mg/ml) against Propionibacterium acnes. Similarly, Diospyros mespiliformis reported for its traditional use to treat ringworm, also displayed noteworthy antimicrobial activity against Trichophyton mentagrophytes (MIC 0.10mg/ml) and Microsporum canis (MIC 0.50mg/ml). The aqueous root extracts of Pentanisia prunelloides combined (1:1) with Elephantorrhiza elephantina displayed synergistic interactions (ƩFIC values 0.31–0.38) against Staphylococcus aureus, gentamycin–methicillin resistant Staphylococcus aureus, Staphylococcus epidermidis and Candida albicans. Fractionation of Aristea ecklonii resulted in the isolation of the known bio-active compound, plumbagin, displaying noteworthy antimicrobial activity (MIC range between 2.00μg/ml and 16.00μg/ml). ConclusionMost of the plant extracts demonstrated pathogen specific antimicrobial effects with a few exhibiting broad-spectrum activities. Positive antimicrobial effects noted for plants such as Elephantorrhiza elephantina and Diospyros mespiliformis used for acne vulgaris and ringworm infections, respectively, give some validation to their reported traditiona l uses. Synergistic interactions noted for Pentanisia prunelloides combined with Elephantorrhiza elephantina validate an enhanced antimicrobial effect when used in combination. Noteworthy antimicrobial activities (MIC range between 2.00μg/ml and 16.00μg/ml) were observed for plumbagin isolated from Aristea ecklonii.

Antifungal activities of essential oils from Southern African medicinal plants against five Fusarium species

In the present study, essential oils from 9 plants traditionally used to treat infectious diseases were tested against five Fusarium spp. using the agar diffusion method. The minimum inhibitory concentrations (MIC) of the oils were determined by the microdilution technique. The killing kinetics of the oils was further evaluated against the fungal organisms. Antifungal activity was exhibited by essential oils from Conyza scabrida, Eriocephallus panculatus, Artemesia afra, Pelargonium graveolons and Mentha peripeta with 100% growth inhibition against all the five Fusarium spp with the zone of inhibition ranging from 10 to 18 mm. The essential oils of C. scabrida and M. piperita were fungicidal to four of the five fungal species tested with minimum fungicidal concentration (MFC) values ranging from 0.95 to 7.50 mg/ml. All the essential oils tested were able to kill the cells at different rates varying from 48 to 100% after 2 days of experimentation. The results of the present study indicate that essential oils tested are promising sources of natural products with which could be used for the control of Fusariuminfections. These results will guide the selection of some plant species for further pharmacological and phytochemical analysis. These results also support the traditional use of these essential oils. Key words: Fusarium spp, anti-fungal activity, essential oils, fungi, Southern Africa, medicinal plants.

Antioxidant and acetylcholinesterase inhibitory activity of selected southern African medicinal plants

Alzheimer's disease (AD) is the most common type of dementia in the aging population. Enhancement of acetylcholine levels in the brain is one means of treating the disease. However, the drugs presently used in the management of the disease have various drawbacks. New treatments are required and in this study, extracts of Salvia tiliifolia Vahl. (whole plant), Chamaecrista mimosoides L. Greene (roots), Buddleja salviifolia (L.) Lam. (whole plant) and Schotia brachypetala Sond. (root and bark) were evaluated to determine their polyphenolic content, antioxidant and acetylcholinesterase inhibitory (AChEI) activity. The DPPH and ABTS assays were used to determine antioxidant activity and Ellman colorimetric method to quantify AChEI activity. Although all four plants showed activity in both assays, the organic extracts of C. mimosoides root was found to contain the highest AChEI activity (IC 50 = 0.03 ± 0.08 mg/ml) and B. salviifolia whole plant had the highest antioxidant activity (ABTS; IC 50 = 0.14 ± 0.08 mg/ml and DPPH; IC 50 = 0.23 ± 0.01 mg/ml). The results suggest that the tested plant species may provide a substantial source of secondary metabolites, which act as natural antioxidants and acetylcholinesterase inhibitors, and may be beneficial in the treatment of AD.

Monoamine oxidase inhibition by southern African traditional medicinal plants

Traditional health care is utilized by a large majority of the population in southern Africa. This is particularly true of treatment for mental health problems. A large part of the treatment regimes used by traditional healers involve numerous herbal preparations. Twenty plants used traditionally were screened for MAO inhibition and specific MAO-B inhibition activity. MAO-B inhibitors are currently employed in the treatment of neurodegenerative related illnesses such as Parkinson's and Alzheimer's disease. A photometric peroxidase linked assay was used to determine the inhibition of the oxidative deamination of tyramine by MAO isolated from rat liver. Ruta graveolens exhibited the best MAO inhibitory activity (ethyl acetate leaf extract = IC 50 5 ± 1 μg/ml, petroleum ether extract = 3 ± 1 μg/ml) and specific MAO-B inhibition (ethyl acetate leaf extract = IC 50 7 ± 6 μg/ml petroleum ether extract = 3 ± 1 μg/ml). Schotia brachypetala, Mentha aquatica and Gasteria croucheri also exhibited good MAO-B inhibition activity. These findings support these plants traditional use and may lead to the discovery of novel MAO inhibitors.

Towards the scientific validation of traditional medicinal plants

A large proportion of the population of developing countries usestraditional medicine alone, or in combination with Western drugs to treat awide variety of ailments. There has seldom been effective collaborationbetween the traditional and Western medical practitioners, largely due tothe perception that the use of traditional and herbal medicines has noscientific basis. With the renewed interest from Western countries in herbalremedies, and the increasingly urgent need to develop new effective drugs,traditionally used medicinal plants have recently received the attention ofthe pharmaceutical and scientific communities. This involves the isolationand identification of the secondary metabolites produced by the plants andused as the active principles in medical preparations. Research into thescientific validation of southern African medicinal plants used in thetreatment of pain and inflammation, hypertension and parasitic diseasesincluding those with anthelmintic, anti-amoebic, anti-bacterial and anti-bilharzia activity, is the current focus of studies conducted at the ResearchCentre for Plant Growth and Development.