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Doctoral Degrees (Research Centre for Plant Growth and Development)

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Browsing Doctoral Degrees (Research Centre for Plant Growth and Development) by Subject "Antibacterial agents."

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    Anti-bacterial and anti-inflammatory activity of medicinal plants used traditionally in Lesotho.
    (2003) Shale, Thato Lucy.; Van Staden, Johannes.; Stirk, Wendy Ann.
    A significant potion of the population in Lesotho relies on traditional medicine to meet its health care requirements. Traditional healers and herbalists were interviewed from Qacha's Nek (Highlands) and Mohale's Hoek (Lowlands) districts in Lesotho on plants used by the Basotho in traditional remedies. Fifteen plants were reported to be used for bacterial infections while thirteen plants were used for diseases associated with inflammation . Plant roots were most often used to make water extracts. Mainly high altitude plants are used with lowland healers obtaining most of their plant material from the highlands, either by collecting them or buying them from highland gatherers. Leaves and roots of plants used to treat bacterial infections were extracted with hexane, methanol and water and the respective extracts screened at 100 mg ml¯¹ for anti-bacterial activity using the disc diffusion bioassay. Seven species displayed very high anti-bacterial activity against both Gram-positive and Gram-negative bacteria. A number of plant extracts had medium inhibitory activity, mostly against Gram-positive bacteria. This activity was mainly found in the root extracts. Six of the thirteen plants screened for anti-inflammatory activity using the cyclooxygenase-1 (COX-1) bioassay had activity above 90%. Hexane and methanol extracts were the most active while water extracts usually had lower activity. Malva parviflora, Eriocephalus punctulatus and Asparagus microraphis exhibited high anti-inflammatory activity from hexane, methanol and water extracts made from leaf and root material. High anti-bacterial activity was also recorded from M. parviflora and E. punctulatus hexane, methanol and water extracts. An investigation on seasonal variation and plant part substitution in medicinal activities for these plants was carried out. Extracts of M. parviflora collected between June 1999 and July 2001 showed variation in anti-bacterial activity. Extracts made from leaves and roots inhibited the growth of both Gram-positive and Gram-negative bacteria. More bacterial strains were inhibited by extracts made from roots collected in cooler months. However, a trend in seasonal activity was not evident for either the roots or leaves because there was no detection of activity in some of the extracts made within the same months or seasons of the adjacent years. Variation in anti-inflammatory was detected for M. parviflora extracts. E. punctulatus leaf extracts did not exhibit any seasonal variation in anti-bacterial activity. Anti-inflammatory activity of E. punctulatus showed seasonal variation with the highest activity noted when material was collected during the cooler months and a decline in activity when collections were made during the warmer months. Hexane, methanol and water extracts made from leaves and roots of A. microraphis did not show any seasonal variation in anti-inflammatory activity. Thus, M. parviflora and E. punctulatus should be collected during the cooler months while A. microraphis can be collected throughout the year. Traditional healers, herbalists and vendors need to be encouraged to use aerial parts in substitution of ground parts which are reported to be highly utilized. Effect of storage on anti-bacterial and anti-inflammatory activities of M. parviflora, E. punctulatus and A. microraphis were monitored. Dried, ground leaf and root material of the three plants was stored in a cold room, at room temperature and in the Botanical Garden where the material was exposed to high and large changes in temperature. Dried hexane and methanol extracts made from leaves and roots of these plants were stored in a cold room and at room temperature. Initially, storage of the plant material under the three storage conditions caused an increase in antibacterial activity of the hexane, methanol and water extracts made from leaf and root material of M. parviflora and E. punctulatus. Storage for a longer period resulted in a decrease in inhibitory activity. TLC fingerprints developed from hexane and methanol extracts made from M. parviflora and E. punctulatus stored in a cold room and at room temperature showed a consistent number and colour of spots during the initial storage period. Prolonged storage resulted in a decline in the number and colour of detected spots. The stored hexane and methanol extracts made from leaves and roots showed a similar trend of increases and decreases in anti-bacterial activity as well as changes in spots with the storage of the extracts. Testing of the effect on anti-inflammatory activity of hexane, methanol and water extracts made from leaves and roots of M. parviflora, E. punctulatus and A. microraphis showed no change in inhibitory activity of hexane extracts obtained from the material and the extracts stored at the three storage conditions. Methanol and water extracts made from leaves exhibited an increase in activity with prolonged storage. Generally, the stability of the inhibitory activity was longer for the stored dried material than the plant extracts. Isolation of biological active compounds from M. parviflora was not successful due to loss in anti-bacterial activity as a result of collection of plant material from a different locality. Anti-inflammatory compounds could not be isolated due to insufficient amount and the synergistic effect of the active compounds . The purified compounds exhibited loss of activity following HPLC purification which then re-appeared upon recombining the fractions. A number of compounds were detected from essential oils of E. punctulatus using GC. Fractions containing these compounds gave positive anti-bacterial activity in the disc-diffusion , bioautographic and MIC bioassays as well as high anti-inflammatory activity with COX-1 and COX-2 anti-inflammatory bioassays. No anti-inflammatory compounds were isolated from A. microraphis.
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    A pharmacological study of some Nigerian medicinal plants.
    (2005) Chukwujekwu, Jude Chinedu.; Van Staden, Johannes.
    Petroleum ether, dichloromethane, and 80% ethanol extracts of 15 plant species collected in Nigeria were screened for in vitro antibacterial, anti-inflammatory and antimalarial activities. Antibacterial activity was tested using the agar diffusion method, while the minimum inhibitory concentrations (MIC) of the active extracts were determined using the microtitre serial dilution method. Most antibacterial activity detected was against Gram-positive bacteria with Staphylococcus aureus being the most susceptible. The highest activity was found in petroleum ether and dichloromethane leaf extracts of Mallotus oppositifolius; petroleum ether, dichloromethane and ethanolic root extracts of Newbouldia laevis; and ethanolic root extracts of Morinda lucida and Canthium subcordatum. Against the Gram-negative bacterium Escherichia coli, the highest activity was found in dichloromethane leaf extracts of Newbouldia laevis, ethanolic root extracts of Phyllanthus amarus, Mallotus oppositifolius, and Canthium subcordatum. A total of 60 plant extracts were screened for antiplasmodial activity. A chloroquine sensitive strain of Plasmodium falciparum (D10) was used. In the assay, the parasite lactate dehydrogenase (pLDH) activity was used to measure parasite viability. About 11 extracts showed promising activity with an IC₅₀ ranging from 2.5 to 13.4 µg/ml. The petroleum ether leaf extract of Hyptis suaveolens had the highest activity (IC₅₀ = 2.5 µg/ml). The cyclooxygenase (COX-1 and COX-2) assays were used to test for anti-inflammatory activity. All the plant species, with the exception of Hedranthera barteri and Picralima nitida showed anti-inflammatory activity. Apart for a few ethanolic extracts, all the activities were recorded with petroleum ether and dichloromethane extracts. Employing bioassay-guided activity fractionation, an antibacterial anthraquinone identified as emodin was isolated from ethanolic root extract of Senna occidentalis. Although this compound had been isolated from other sources, this was the first report of isolation from Senna occidentalis. Using a similar approach a novel antimalarial diterpenoid was isolated from the petroleum ether leaves extract of Hyptis suaveolens. It had IC₅₀ of 0.1 µg/ml. This new compound is worthy of further investigation and may act as an important lead compound for future antimalarial drugs.