The study of the antimicrobial properties of selected plants growing in the Free State

[摘要] English: The Free State province has a rich diversity of indigenous woody plant species that exhibitantimicrobial activity towards both plant and human pathogens. Most of the province (about72%) is located within the Grassland Biome, only about 21% is in the Nama-Karoo Biome,6.64% in the Savanna Biome and with the Forest Biome making up only 0.05% of theprovince. The location of the province in what is mostly the Grassland Biome has resulted inextensive animal husbandry and intensive crop production. Grazing by animals, especiallycattle and sheep, continues to have detrimental effect on the local pristine vegetation. On theother hand, intensive crop production, though done with utmost care in most cases, is alsoresulting in environmental degradation through water pollution by herbicides, bothantimicrobials and insecticides. Chances are that some of these pesticides might end up in thefood consumers buy, and may lead to health problems.There is great awareness in the Free State province for the need to conserve the environmentand the fact that conservation can only be done through the knowledge of the vegetationecology of the province. Towards this end, a lot of studies on the vegetation ecology of thedifferent areas of the province have been attempted by a number of authors. Despite theexistence of information on the vegetation ecology, the Free State still had to be mapped forplants with biological activities, in our case, antimicrobial activity. This exercise wassuccessfully done.Antimicrobial screening of the crude extracts was done as a preliminary screen to determinewhich plant species exhibited this activity. Bench top assays were used due to their reliability,speed and cost effectiveness. The screen gave valuable information on the antimicrobialproperties of these selected plants. By referring to their phytochemical compositions mliterature, we were able to conclude why they are used in ethnopharmacology, as well asdetermine the active principles. Antibiotic plant species with ethnopharmacological value can also be used as agrochemieals against plant pathogenic miroorganisms with success. Theextracts of selected plant species in our investigations were tested against both plant andhuman pathogens with encouraging results. The general absence of antifungal activitytowards plant pathogenic fungi was attributed to lower doses of the extracts used, the crudenature of the extracts as well as the the probable presence of growth promoters for the fungi orthe general absence of active antifungal substances by nature.The crude extracts of seven plant species out of a total of twenty six exhibited the mostoutstanding antibacterial activity as evidenced by broad spectrums of activity and largerinhibition zones in comparison with the rest of the plant species. The most resistant bacterialpathogen towards the crude extracts was Erwinia carotovora pv. carotovora while the leastresistant was Moraxella catarrhalis. From the seven most active plant species, it was decidedto do further investigations on Euclea crispa subsp. crispa. This was due to the fact that it iswidely used in ethnopharmacology in areas like Kwa-Zulu Natal and also that it is one of themost common plant species in the province as well as in the country as a whole.The crude and semi-purified (liquid-liquid separation) extracts of E. crispa subsp. crispashowed antibacterial activity towards human pathogenic bacteria to varying degrees. The ethylacetate fraction was the most active however, since only three human pathogenic bacteria werenot inhibited by it. Klebsiella pneumoniae was the most resistant human pathogenic bacterium.With regards to plant pathogenic bacteria, generally, only the ethyl acetate fraction and (thecrude extract) showed activity against all the bacteria. Antifungal screening of the semipurifiedextracts with human pathogenic fungi also showed that most of the antifungal activitywas located in the ethyl acetate fraction. No antifungal activity was observed with the hexanefraction. Due to the more complex nature of the crude extract, further phytochemical studieswere carried out only with the ethyl acetate fraction, the most active semi-purified fraction.Investigations into the general phytochemical profile of the ethyl acetate fraction of E. crispasubsp. crispa revealed that the plant extract contained essential oils, bitter principles, saponins, alkaloids and phenolic compounds; the first three being terpenoid derivatives. Bitter principlesare in some cases reported as being mixtures of different classes. A terpenoid that testedpositive for bitter principles and for saponins as well as possessing a steroid-like structure wasisolated from the ethyl acetate fraction. This compound was active against M catarrhalis. Alsoisolated from the ethyl acetate fraction and showing antimicrobial activity were five flavonoidsidentified as hyperoside, quercitrin, catechin, epicatechin and gallocatechin. The most activeflavonoids were epicatechin and hyperoside which inhibited the growth of Streptococcuspneumoniae and Haemophilus injluenzae respectively.The activities of the isolated flavonoids towards human pathogenic bacteria were lower thanthat that of the more complex ethyl acetate fraction. The conclusion arrived at was that thesecompounds function in synergy in the latter more complex fraction. Since most of the plantextracts are used in the form of complex mixtures in ethnopharmacology, a suggestion wasmade to use the ethyl acetate fraction in its complex form. It was further acknowledged that theuse of complex mixtures instead of pure compounds does not eliminate the need to determinethe chemical composition of the complex mixtures. This is necessary to determine the dosagesand toxicity of the constituents of the extracts.In conclusion, it can be said that valuable information on the antimicrobial properties ofselected plant species growing in the Free State Province was obtained during the course of ourinvestigations. Also of value is the information on the distribution of these species in relationto biomes, geology and soil types. The availability of literature on the vegetation ecology ofdifferent parts of the province was also of immense help to us during this investigation.

[发布机构] University of the Free State