J.J.M. Meyer

The antimicrobial activity of 3,5,7-trihydroxyflavone isolated from the shoots of Helichrysum aureonitens

Extracts from Helichrysum aureonitens are used topically by the indigenous people of South Africa against infections. The antimicrobial activity-guided fractionation by bioautography of the acetone extract from the aerial parts of H. aureonitens led to the isolation of 3,5,7-trihydroxyflavone (galangin). Evaluation of the antibacterial activity of the compound against ten randomly selected bacteria indicated significant activity against all the Gram-positive bacteria tested with the minimum inhibitory concentration (MIC) ranging from 0.1 to 0.5 mg/ml. The compound was not active on Gram-negative bacteria except for Enterobacter cloacae which was significantly inhibited at an MIC of 0.1 mg/ml. Galangin indicated considerable activity against the fungi tested with the exception of Cladosporium herbarum. Penicillium digitatum and P. italicum appeared to be particularly susceptible at a concentration of 0.01 mg/ml.

In vitro inhibition of drug-resistant and drug-sensitive strains of Mycobacterium tuberculosis by ethnobotanically selected South African plants

Twenty South African medicinal plants used to treat pulmonary diseases were screened for activity against drug-resistant and drug-sensitive strains of Mycobacterium tuberculosis. A preliminary screening of acetone and water plant extracts against a drug-sensitive strain of Mycobacterium tuberculosis, H37Rv, was done by the agar plate method. Fourteen of the 20 acetone extracts showed inhibitory activity at a concentration of 0.5 mg/ml against this strain. Acetone as well as water extracts of Cryptocarya latifolia, Euclea natalensis, Helichrysum melanacme, Nidorella anomala and Thymus vulgaris inhibited the growth of M. tuberculosis. Given the activity of 14 acetone extracts at 0.5 mg/ml against the drug-sensitive strain by the agar plate method, a further study was done employing a rapid radiometric method to confirm the inhibitory activity. These active acetone extracts were screened against the H37Rv strain as well as a strain resistant to the drugs isoniazid and rifampin. The minimal inhibitory concentration of Croton pseudopulchellus, Ekebergia capensis, Euclea natalensis, Nidorella anomala and Polygala myrtifolia was 0.1 mg/ml against the H37Rv strain by the radiometric method. Extracts of Chenopodium ambrosioides, Ekebergia capensis, Euclea natalensis, Helichrysum melanacme, Nidorella anomala and Polygala myrtifolia were active against the resistant strain at 0.1 mg/ml. Eight plants showed activity against both strains at a concentration of 1.0 mg/ml.

Antimicrobial activity of the crude extracts and compounds from Ficus chlamydocarpa and Ficus cordata (Moraceae)

The aim of this study was to evaluate the antimicrobial activity of the methanol extracts from Ficus chlamydocarpa (FCR), Ficus cordata (FCB), mixture of the two plants (FCM), as well as that of the isolated flavonoids Alpinumisoflavone (2), Genistein (3), Laburnetin (4), Luteolin (5) (isolated from FCR), Catechin (7) and Epiafzelechin (8) (isolated from FCB). Mycobacteria, fungi, Gram-positive and Gram-negative bacterial species were tested for their susceptibility to the above samples. The microplate dilution and radiometric respiratory methods were used to determine the susceptibility testing of the samples against Mycobacterium smegmatis and Mycobacterium tuberculosis, respectively. The disc diffusion assay was used to determine the sensitivity of the samples, whilst the micro-dilution method was used for the determination of the minimal inhibition concentration (MIC) and the minimal microbicidal concentration (MMC) against fungi, Gram-positive and Gram-negative bacterial species. All the samples except compound 7 were found to be active to Mycobacterium smegmatis and the MIC ranged from 0.61 to 312.50microg/ml. Compound 4 showed the best activity against Mycobacterium tuberculosis exhibiting an MIC of 4.88microg/ml. The results of the diffusion test indicated that the crude extract from FCB, FCM as well as compounds 5 and 8 were able to prevent the growth of all tested (fungi, Gram-positive and Gram-negative bacteria) organisms. The inhibition effect of the crude extract from Ficus chlamydocarpa was observed on 10 (62.5%) of the 16 tested microorganisms (excluding mycobacteria) whereas that of compounds 4, 2 and 3 was respectively noted on 14 (87.5%), 8 (50.0%) and 7 (39.9%) of the tested microbial species. FCB was found to be more active than FCR on most of the tested organisms. The results provided evidence that the studied plants extract, as well as some of the isolated compounds might be potential sources of new antimicrobial drug.

The potential of South African plants against Mycobacterium infections

ETHNOPHARMACOLOGICAL RELEVANCE In South Africa, tuberculosis (TB) caused by Mycobacterium tuberculosis is the most commonly notified disease and the fifth largest cause of mortality, with one in ten cases of TB resistant to treatment in some areas. Many plants are used locally in traditional medicine to treat TB-related symptoms. AIM OF THE STUDY The aim was to summarize currently available knowledge on South African plants used to treat TB symptoms, and antimycobacterial efficacy of plant-derived extracts and compounds. MATERIALS AND METHODS The traditional uses of plants for respiratory ailments and TB were collated and tabulated. The antimycobacterial activity tests of extracts and chemical constituents of several of these plants and others using different methods and target organisms were summarized. RESULTS Almost 180 plants used for TB-related symptoms in South African traditional medicine were documented. About 30% of these have been tested for antimycobacterial efficacy, mostly against fast-growing, non-pathogenic Mycobacterium species. CONCLUSIONS Many plant species are used in traditional South African medicine to alleviate symptoms of TB, and several interesting leads have originated for further inquiry following in vitro antimycobacterial activity evaluation. However, much work remains to be done on the systematic assessment of anti-TB efficacy of local plants against pathogenic Mycobacterium species, both in vitro and in vivo.

Antibacterial activity of linoleic and oleic acids isolated from Helichrysum pedunculatum : a plant used during circumcision rites

The antibacterial activity-guided fractionation of the dichloromethane extract of leaves of Helichrysum pedunculatum resulted in the isolation of linoleic and oleic acids. Linoleic acid inhibited the growth of all the Gram-positive bacterial species tested with the minimum inhibitory concentration (MIC) varying between 0.01 and 1.0 mg/ml. Oleic acid was active against three of the five Gram-positive bacteria at a MIC of 1.0 mg/ml. Both compounds were inactive against the Gram-negative species tested. A synergistic effect between the two fatty acids was observed against Staphylococcus aureus and Micrococcus kristinae.

Antibacterial activity of Helichrysum aureonitens (Asteraceae)

The antibacterial activity of extracts from Helichrysum aureonitens was investigated. The dichloromethane extract was active against all five gram positive bacteria tested and the methanol extract was active only against Bacillus cereus, B. pumilus and Micrococcus kristinae, while the water extract had no activity against any of the organisms. None of the extracts inhibited the growth of the five gram negative bacteria tested.

Antiviral activity of galangin isolated from the aerial parts of Helichrysum aureonitens.

The in vitro antiviral activity of galangin (3,5,7-trihydroxyflavone), the major antimicrobial compound isolated from the shoots of Helichrysum aureonitens, was investigated against herpes simplex virus type 1 (HSV-1), coxsackie B virus type 1 (Cox B1), adenovirus type 31 (Ad31) and reovirus. At concentrations ranging from 12-47 micrograms/ml galangin showed significant antiviral activity against HSV-1 and CoxB1, limited activity against reovirus, and no antiviral activity against Ad31.

In vitro antiplasmodial activity and cytotoxicity of ethnobotanically selected South African plants.

The resistance of Plasmodium spp. to currently used drugs has become a serious problem and efforts are being directed in obtaining new drugs with different structural features. One option favoured is the search for new plant derived antimalarial drugs. Bark and leaves of 20 extracts from 14 South African plant species were tested for in vitro antiplasmodial activity by means of the flow cytometric test. The most active extract of each species giving more than 70% inhibition at 50 microg/ml was selected for determination of IC(50) values. Two extracts had IC(50) values below 2 microg/ml, another seven had IC(50) values between 2 and 5 microg/ml while one had an IC(50) of 10.1 microg/ml. Chloroquine had an IC(50) of 0.043 microg/ml. Cytotoxicities of the five most active extracts at 50 microg/ml were determined with the monkey kidney cell toxicity test and the ID(50) values ranged between 35 and 100 microg/ml.

Inhibition of herpes simplex virus type 1 by aqueous extracts from shoots of Helichrysum aureonitens (Asteraceae)

Helichrysum aureonitens, a southern African medicinal plant reported to have antibacterial properties, was evaluated for antiviral activity against herpes simplex virus type 1 (HSV-1) in vitro. The crude aqueous extract from shoots of H. aureonitens at a concentration of 1.35 mg/ml (w/v) showed significant antiviral activity on HSV-1 in human lung fibroblasts as demonstrated by the absence of a cytopathic effect.

Inhibition of drug-sensitive and drug-resistant strains of Mycobacterium tuberculosis by diospyrin, isolated from Euclea natalensis.

The binaphthoquinoid, diospyrin, was isolated from Euclea natalensis A.DC., and evaluated for its activity against drug-sensitive and drug-resistant strains of Mycobacterium tuberculosis. The minimal inhibitory concentration (MIC) of diospyrin was found to be 100 microg/ml for all the M. tuberculosis strains.