Start main page content

Recently Added Items on WIReDSpace

Aspects of high-level trimethoprin resistance in gram-negative bacteria isolated in South Africa

Aspects of high-level trimethoprin resistance in gram-negative bacteria isolated in South Africa Wylie, Barbara A Trimethoprim is a broad-spectrum antimicrobial agent frequently used either in combination with sulphamethoxazole (cotrimoxazole) or alone in the treatment of urinary and respiratory tract infections. Since the introduction of this drug in 1969 resistance to it has been monitored in several centres in Europe continuously but only intermittently in the United States of America and developing countries in Africa, Asia, Central and South America. In Europe the incidence of trimethoprim resistance has increased significantly in the last 20 years. In developing countries no trends have been established but the incidence of resistance appears to be greater in these countries than in Europe or the USA. A thesis submitted to the Faculty of Medicine, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements of Doctor of Philosophy. Johannesburg 1991

An assessment of the impacts of climate and land use/cover changes on wetland extent within Mzingwane catchment, Zimbabwe

An assessment of the impacts of climate and land use/cover changes on wetland extent within Mzingwane catchment, Zimbabwe Sibanda, Sethi Wetlands ecosystems are amongst the most diverse and valuable environments which provide a number of goods and services pertinent to human and natural systems functioning yet they are increasingly threatened by anthropogenic and climatic changes. This thesis, examines the impact of climatic trends and variations, and land use/land (LU/LC) cover changes on wetland extent within Mzingwane catchment, south-western of Zimbabwe. An attempt is made to establish how the two stressors (climate and LU/LC changes) modify areal extents of wetlands over time, grounded on the hypothesis that, climate and LU/LC related changes impact on wetland ecosystems resulting in their degradation, shrinking in size and in some cases overall loss. To achieve the broader objective of the study, a number of parametric and non-parametric statistical analyses were employed to quantify and ascertain climate variability and change in Mzingwane catchment through the use of historic and current climatic trends in rainfall and temperature (T). Remote sensing data was used for wetland change analysis for the period between 1984 and 2015as well as future land cover predictions based on CA-Markov Chain model. LU/LC changes on nested wetlands were modelled at catchment level. In addition the study simulated future rainfall and extreme events and their implications on wetland dynamics using Regional Climate Models derived from CORDEX data. Trends in annual Tmax significantly increased (p<0.05) at an average of 0.16 decade-1 in 80% of the stations. Results of extreme events indicate a statistically significant increase (p<0.05) in the occurrence of extreme dry periods since the 1980s. Rainfall variability results show that contemporary mean annual rainfall has not changed from that measured during the historic period of 1886-1906. However, the number of rainy days (>=1mm) has decreased by 34%, thus suggesting much more concentrated and increased rainfall intensity. A notable shift in both the onset and cessation dates of the rainy season is recorded, particularly during the 21st century, which has resulted in a significant reduction (p<0.05) in the length of the rainy season. Land change analysis results show a decline in woodland and wetland cover which could be resulting from both human and natural factors. Major conversions are from wetland cover to crop field, suggesting agricultural encroachment onto wetland areas. Wetland area thus significantly decreased by 60.16% (236, 52 ha) in the last 30 years (p < 0.05). CA-Markov model results for the years 2025, 2035 and 2045 predicted an overall increase in the crop field areas at the expense of woodland and wetland areas. LU/LC modelling results suggest that LU/LC changes modify wetland hydrology which consequently influences wetland areal extent. Trend results for projected rainfall suggest a significant decreasing trend in future rainfall (2016-2100) at p<0.05. In addition, a general decreasing trend in the number of rainy days is projected for the future climate although the significance and magnitude varied with station location. Regional Climate Models projections suggest an increased occurrence of future extreme events particularly towards the end of this century. The findings are important for developing appropriate sustainable and adaptive strategies given climate changes as well as designing catchment level wetland management approaches aimed at sustaining wetland ecosystems for the current and future generations. Any future efforts towards protection of the remaining wetlands should be combined with developing a sustainable relationship between social and ecological systems which will enable communities to adapt to the effects of changing climates. A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy(Geography and Environmental Science). Johannesburg, June 2018.

The role of mononuclear cells in tuberculosis

The role of mononuclear cells in tuberculosis Sussman, Garth Sonicates derived from Mycobacterium tuberculosis suppressed lymphocytes proliferation. Pulsing of monocytes with mycobacterial sonicates resulted in the release of high molecular weight lipids. Both these lipids and those prepared by column fractionation of mycobacterial sonicates suppressed lymphocyte blastogenesis.This effect was due to the activation and not the proliferation of CD8+ lymphocytes by the lipid containing mycobacterial fractions of Mr>200kDa that could be obtained in vitro by column fractions. Thesis presented in fulfilment of the requirements governing the degree of Philosophy in the School of Medicine, University of the Witwatersrand. Johannesburg

Impact of biocontrol agents on Lantana camara L. (Verbenaceae) in the lowveld region of Mpumalanga, South Africa

Impact of biocontrol agents on Lantana camara L. (Verbenaceae) in the lowveld region of Mpumalanga, South Africa Katembo, Naweji Lantana camara L. (sensu lato) (Verbenaceae) remains one of the worst invasive alien plants in most tropical and subtropical parts of the world, including South Africa. Despite a concerted biological control (biocontrol) effort, with 45 biocontrol agents released against the weed worldwide since the early 1900s to date, L. camara control is far from satisfactory in most areas, including the study area. In 2012, during the initial stage of this work, a plant-ecological survey was conducted in riparian areas along the Sabie River, across an altitudinal gradient, and also in the adjacent forest plantation areas, in the province of Mpumalanga (South Africa). As a follow-up to two separate previous studies in the same area (1996/7 and 2005), aimed at determining the effectiveness of the ‘Working for Water’s (WfW) invasive alien plant (IAP) control programme, this work is another milestone in a long-term monitoring study. However, despite 16 years (1996/7-2012) of integrated IAP-control operations in the area, the WfW programme was only able to successfully remove larger overstorey IAPs, which opened-up the canopy and reduced competition, creating a conducive growing environment for an amalgamation of understorey IAPs, including L. camara, whose spread and densification were still on the rise. Biocontrol is regarded as a better alternative for long-term, sustainable and environmentally friendly IAP control, compared to the conventional mechanical and chemical methods. Most L. camara biocontrol agents introduced into South Africa have not yet had their full impact quantified under field conditions. This work is novel in that, for the first time, it quantifies the combined impact of the ‘old plus new’ suite of L. camara biocontrol agents, on the growth, reproduction and biomass of the weed under field conditions, in an inland area, through an insecticidal exclusion experiment, using carbofuran. Five prominent biocontrol agents occur on L. camara at the study sites, namely the fruit-mining fly, Ophiomyia lantanae (Froggatt) (Diptera: Agromyzidae); the shoot-sucking bug, Teleonemia scrupulosa Stål (Hemiptera: Tingidae); the defoliating moth, Hypena laceratalis Walker (Lepidoptera: Noctuidae); the leaf-mining beetle, Octotoma scabripennis Guèrin-Mèneville (Coleoptera: Chrysomelidae); and the fungal leaf-spot pathogen, cf. Passalora sp. (Chupp) U. Braun & Crous var. lantanae. During the course of this study, an additional agent, the flower-galling mite, Aceria lantanae (Cook) (Acari: Trombidiformes: Eriophyidae), was released and successfully established at lower altitudes (~843 m), showing an affinity for the dark-pink L. camara variety over others in the study area, namely light-pink and red-orange. Agent impact was difficult to measure because the activity of carbofuran in exclusion plants (carbofuran-treated L. camara plants) was short-lived; and therefore the impact of biocontrol agents on L. camara, which appeared to be negligible, may have been underestimated. Despite failing to maintain the ‘exclusion’ plants biocontrol agent-free through the application of carbofuran, there were reductions of 28% in the number of side-stems per plant, 31% fewer seeds in the soil seedbank, and 29% lower seed production, in ‘biocontrol’ plants compared to ‘exclusion’ plants. Although these differences were not statistically significant, they suggest that the present suite of biocontrol agents slightly reduces the vegetative and reproductive growth of L. camara. To achieve significant biocontrol of L. camara in inland areas, it seems necessary to introduce additional agents, which are well adapted to inland climatic conditions. The effects of micro-environmental factors, namely altitude and the degree of shading, were also investigated. Some biocontrol agents, such as T. scrupulosa, exhibited feeding phenological plasticity, resulting in it maintaining its presence at different altitudinal levels throughout the seasons. The performance of the suite of biocontrol agents, except A. lantanae, was, also, not limited by plant varietal differences. Additional research on biological and integrated control of L. camara is required. Keywords: Biocontrol; Biological invasion; Carbofuran; Insecticidal exclusion; Invasive alien plants; Lantana camara; Post-release evaluation. A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the academic requirements for the degree of Doctor of Philosophy School of Animal, Plant and Environmental Sciences. Johannesburg, June 2018.