Call number: LD2668 .T4 1961 M58

Phytophthora parasitica, P. citrophthora, and other plant pathogenic fungi were isolated from re-cycled water used to irrigate citrus and other crops. The several propogules of P. parasitica were then studied to determine their survival capabilities in soil and irrigation water. Chlamydospores of P. parasitica were present in field soils from foot-rot infested citrus groves and persisted for at least 60 days in air-dried or moist soils. They germinated in irrigation water or moist soil and formed sporangia within 16 hr. Sporangia were also present in these field soils and survived for at least 60 days in moist soil. They germinated, releasing zoospores into irrigation water 5 min after being inundated. Zoospores were not present in water flooded on air-dried field soil until after 20 hr incubation. Citrus leaves became infected by zoospores within 15 min when placed in zoospore infested water. Although they remained motile in irrigation water for up to 20 hr at 20 C, zoospores encysted when agitated or upon the addition of nutrients, orange peel, or citrus leaves. At low nutrient levels (< 5 mg glucose/liter of sterile distilled water) zoospores germinated and upon cessation of growth the protoplasm contracted within the hyphae and pseudo-septa were formed. Empty cysts or hyphae often lysed; remaining hyphal fragments containing protoplasm survived for at least 40 days at 25 C in untreated waste water and resumed growth upon addition of nutrients. At higher nutrient levels (10-1,000 mg glucose/liter of sterile distilled water) the hyphal tips often produced appressorium-like structures when in contact with the container surface. Exudates from orange peel or citrus leaves stimulated similar activity. The appressorium-like structures usually germinated to produce microsporangia when the nutrients were replaced with untreated irrigation waste water. Some microsporangia persisted in untreated waste water at 25 C for 60 days but most germinated sooner, producing only a single zoospore. Mycelial inoculum from these zoospores was pathogenic to roots of citrus seedlings. Results indicate that P. parasitica is spread by re-cycled irrigation water and that zoospores, or structures produced by them, can play a significant role as survival or dispersal units in re-cycled water.

No description available.

Streptococcus pneumoniae is a highly diverse and adaptable opportunistic pathogen that can infect and colonise different niches within the human host to cause a wide range of invasive disease (sepsis and meningitis) and noninvasive disease (pneumonia, otitis media and sinusitis). The molecular mechanisms that contribute to the different patterns of pneumococcal infection remain largely unknown. This thesis aims to determine the physiological and proteomic responses that allow the pneumococcus to survive and adapt to invasive and non-invasive sites. The comparative proteomic analyses of clinical S. pneumoniae isolates recovered from blood cultures (classified as invasive site isolates) and mucosal surfaces such as sputum, skin and ear swabs (classified as non-invasive site isolates) was initiated. The pneumococci were grown in vitro under standard conditions and the total cellular bacterial proteins extracted and analysed using both gel based and non-gel based proteomic approaches. Analysis of the pneumococcal isolates by two-dimensional polyacrylamide gel electrophoresis (2DGE) revealed that a high degree of heterogeneity existed between the pneumococcal isolates particularly among isolates in the invasive site isolates. Differential patterns of protein synthesis were observed that discriminated the pneumococcal isolates according to their sites of isolation. These were proposed to be associated with the bacterial adaptation to invasive and non-invasive sites of infection. Mass spectrometry was used to identify selected significant (ANOVA, p < 0.05) protein spots, which were further categorised into functional groups by Gene Ontology analysis. An extension of the 2DGE data using an integrated approach comprising bioinformatics, surfome analysis and a shotgun proteomic workflow provided a comprehensive qualitative and quantitative analyses of the pneumococcal intracellular and cell-surface proteomes. Proteins potentially involved in pneumococcal niche-specific adaptation and surface proteins with potential for further investigation and inclusion in the pipeline of vaccine candidates were identified. Quantitative regulation of proteins involved in energy metabolism, genetic competence, stress response, surface adhesion and virulence were considered important for pneumococcal adaptation to invasive and non-invasive sites. The anatomical sites colonised by the pneumococcus vary in their V availability for iron. The 2DGE method was also used on selected pneumococcal isolates from the two sites of infection to define the proteome variability linked to the effect of iron starvation that may contribute to the different disease outcomes associated with pneumococcal infections. The iron restricted condition was generated by cation depletion of the growth medium using Chelex-100. Quantitative differences in protein abundance were demonstrated that correlated with pneumococcal adaptation to iron restriction. The identification of selected significant spots by liquid chromatography-mass spectrometry and systems biology analysis of the identified proteins contributed to the elucidation of the molecular mechanisms underlying pneumococcal survival under iron limitation. The expression/repression of proteins functionally associated with metal ion binding, oxidative stress response, translation and virulence mainly constituted the pneumococcal adaptive responses to growth under conditions of limited iron availability. The data presented in this thesis extended our understanding of the molecular events underlying pneumococcal physiological adaptation and provide the basis of future work in this area.

Assignment (MCur)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

Mycoses refer to infections caused by different fungal infections. Some mycoses can be defeated by the hosts themselves attributed to the functional immune systems before severe symptoms appear. However, in immune-compromised patients, including those suffering from AIDS or receiving chemotherapies, those mycoses become lethal. They are called opportunistic systemic mycoses. Among them, two types of the most deadly mycoses, especially for AIDS patients in Southeast Asia, are cryptococcsis and penicillosis, caused by Cryptococcus neoformans (C. neoformans) and Penicillium marneffei (P. marneffei), respectively. Both of them have their own virulence factors to enhance their pathogenicities and survival in hosts. Active research to explore these virulence factors in these two funguses is ongoing. Two proteins from these two pathogens were found to be putative novel virulence factors, MP1p from P. marneffei, and CPL1 from C. neoformans. Collaborators have successfully found that MP1p strongly bound arachidonic acids (AA), the sole precursor of paracrine signaling molecules essential to the onset of inflammatory responses, by various functional studies. This led to the hypothesis that MP1p might be able to suppress inflammatory responses and subsequent immune responses via removal of AA from macrophages engulfed P. marneffei. In this work, X-ray crystal structures of MP1p’s ligand-binding domain 2 (LBD2) from P. marneffei (strain MP1) overexpressed in E. coli, in complex with one and two AA molecules, were successfully solved by molecular replacement method. The resolutions were up to 1.45 Å and 1.50 Å respectively. These structures revealed detailed interactions between MP1p-LBD2 and AA.A possible ligands-dependent dimer-monomer transition in LBD2 was also revealed by both analytical size exclusion chromatography and crystallography. Full length CPL1 overexpressed in yeast was also successfully purified and crystallized. A 3.0 Å native dataset was collected. Heavy atoms derivatives of the crystals would be produced in order to solve the structure via experimental phasing methods. The structural determination of these virulence factors may provide molecular bases at atomic resolution for the developments of drugs targeting MP1p and CPL1 by structure-based drug design to treat, particularly, penicillosis and cryptococcsis in immune-compromised patients. / published_or_final_version / Physiology / Master / Master of Philosophy

Thesis (MTech. degree in Environmental management.)-Tshwane University of Technology, 2012 / Aims to assist communities on the selection of suitable household water treatment devices/systems that can produce bacteriologically safe drinking water of high quality, at low cost, five selected household water treatment filters were used in this study.

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

No description available.