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

Thesis (M. S.)--Chemical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Dr. Rachel Chen; Committee Member: Dr. Athanassios Sambanis; Committee Member: Dr. Sankar Nair. Part of the SMARTech Electronic Thesis and Dissertation Collection.

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

No description available.

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There are a number of unanswered questions regarding new caries preventive methods such as ozone treatment as well as novel caries detection methods that monitor and evaluate these preventive methods. This thesis seeks answers to some of these questions. Aims: Paper I investigates the in vitro sealing capacity of a novel ozone delivery system and its re-suction capacity. Paper II studies the in vitro antibacterial effect of ozone on cariogenic bacterial species with and without the presence of saliva and its possible effect on the saliva proteins. Paper III assesses the in vitro validity of laser-induced fluorescence (LF) measurements, visual inspection (colour), and tactile examination (surface texture) on root caries lesions and correlates these with histopathological measurements of lesion depths.  In addition, Paper III investigates how inter-device, inter-examiner, and intra-examiner levels influence LF reading agreements and whether lesion colour and surface texture influences LF readings. Paper IV evaluates the in vivo effect of ozone and fluoride varnish treatments on occlusal caries in primary molars. Material and methods: Paper I: Full ozone application cycles, including the re-suction period, and interrupted cycles with displacement of the cup during the delivery cycle were studied using an ozone air analyser. Paper II: Ozone gas was exposed to the bacteria in the solution’s buffer and saliva via a tube connected to the ozone generator for 10, 30, and 60 seconds. Paper III: Calibrated examiners assessed lesion colour and surface texture and performed measurements with two LF devices for three separate one-week intervals.  Sections (300µm thick) of 64 out of 93 teeth were obtained and examined under a microscope. Lesion depth was assessed with two references: from the delineated borderline of the original exposed root surface (ref I) or, if loss of surface continuity, the absolute lesion depth (ref II). Paper IV: The split mouth study was conducted in two parts. The participants in part A were children (mean age 4.8 years) with medium-high caries risk. Inclusion criteria were bilateral matched pairs of cavitated or non-cavitated occlusal lesions in primary molars (Ekstrand index score ≤ 3). Children in part B (mean age 4.5 years) with low-medium caries risk had pairs of non-cavitated lesions only (Ekstrand index score ≤ 2a). The assessments and treatments with ozone and fluoride varnish were performed at baseline and at three, six, and nine months. At the 12-month follow-up, only assessments were performed. Results: Paper I: Ozone leakage levels varied between 5.2 and 9.8 µg/m3. Paper II: In the salt buffer, 92%, 73%, and 64% of the initial numbers of A. naeslundii, S. mutans, and L. casei, respectively, were killed after 10 s ozone exposure and approximately 99.9% of the bacteria were dead after a 60 s exposure. After 10 and 30 s but not after 60 s exposure to ozone, S. mutans and L. casei were less efficiently killed in saliva compared to in the salt buffer. Various saliva proteins were degraded by ozone after the 60 s exposure. Paper III: The correlation between LF readings and histological depth was low with values ranging from 0.22 (p ˃ 0.05) to 0.31 (p < 0.05). The LF devices were significantly correlated with discolouration and with a surface texture denoted as hard. A significant correlation was found between colour and histological depth. No significant correlation was found between surface texture and histological depth. The reliability, evaluated as intra-class correlation coefficient, was 0.99 for intra-examiner, 0.97 for inter-examiner, and 0.98 inter-device level. Large differences were found between two consecutive measurements and high measurement errors indicated considerable deviation of individual measurements.Paper IV: In the first 15 pairs of part A, eight lesions treated with ozone and nine treated with fluoride, including all cavitated lesions, progressed to failure, i.e., required operative treatment during the study time. Due to non-acceptable results, the sample collection was discontinued because of ethical reasons. In part B, of 35 pairs, one of the ozone treated lesions failed at 12 months. A small shift towards increased VI scores was recorded for both ozone and fluoride lesions in this second part. Conclusions: - The ozone delivery system can be considered a safe system with low leakage levels in air, also with accidental displacements. - The cariogenic species S. mutans, L. casei, and A. naeslundii were sensitive to ozone gas treatment. The presence of saliva hampered the antibacterial effect of ozone. A low correlation between the LF readings and the histopathological depth of root caries lesions was shown. The LF device was found not to be appropriate for application to root caries diagnosis. - Neither ozone nor fluoride varnish treatments arrested the progression of cavitated occlusal caries lesions. In low and medium caries risk children non-cavitated occlusal lesions remained mainly unchanged during the study period.  No difference in the effect of ozone and fluoride varnish treatments on occlusal caries in primary molars was seen.

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No description available.

In this study bioluminescence-marker systems were used to investigate the fate of two genetically engineered degradative bacteria in soil under different conditions. These bacteria were chromosomally <I>lux-</I>marked <I>Alcaligenes eutrophus </I>H850 Lr with <I>lux</I>AB genes which was able to degrade polychlorinated biphenyls (PCBs), and <I>Pseudomonas stutzeri </I>P16. <I>P. stutzeri </I>P16 was genetically marked with the <I>lux</I>AB <I>tet</I> cassette by insertional mutagenesis using mini Tn5-transposons and was characterised for <I>lux</I> gene stability, phenanthrene degradability and sensitivity to aldehyde. Insertion of <I>lux</I> gene into genome of <I>P. stutzeri</I> P16 provided a novel strain with lower maximum specific growth rate and less sensitivity to high concentrations of phenanthrene in liquid culture. Survival and activity of <I>P. stutzeri</I> P16 <I>lux</I>AB4 was further investigated in soil amended with low and high concentrations of phenanthrene. Initially high concentrations of phenanthrene had a less toxic effect on viable cell concentrations and luminescence activity of genetically engineered <I>P. stutzeri</I> P16 comparing with its wild type showing that <I>lux</I>-marking the above degradative strain made the marked strain more suitable for environmental application in heavily polluted sites. However, resistant cells to high concentration of phenanthrene were not able to survive longer than those which was inoculated to microcosms with lower concentrations of phenanthrene. This indicates that toxicity of the target compound and its concentration have to be considered before releasing the GEMs. Degradation of phenanthrene was enhanced in both sterile and non-sterile soil inoculated with <I>P. stutzeri </I>P16 <I>lux</I>AB4. This study could be used as model for further investigated of degradation of other PAHs such as fluoranthene, benz[a]anthracene, benzo[a]pyrene, by degradative bacteria and also monitoring the survival and activity of those bacteria in the environment using bioluminescence-marker systems.

The aim of this work was to develop and test a mathematical model for DNA transfer by conjugation which considered spatial separation of cells on surfaces. Model parameters include the initial donor and recipient numbers, maximum specific population growth rate, microcolony radial extension rate, maximum cell yield, maximum incubation time, standard deviation of the mean intercellular distance (σ), cellular area and area available for colonization. Sensitivity analysis indicated that growth areas and σ had the greatest effects on conjugation. The model was extended to consider the presence of a strain that did not conjugate and its effect on plasmid transfer. Filter matings with <I>Pseudomonas fluorescens</I> MON787 RP4 as the plasmid donor and <I>P. fluorescens</I> MON787 R <I>lux</I> as recipient were used to test the model. Model predictions were generally accurate but transconjugants were consistently underestimated. This was attributed to intercellular distances not following a strict Gaussian distribution. Nevertheless, predicted and experimental data were qualitatively similar, which increased confidence in the validity of the mechanisms proposed. Conjugation occurred over a wide range of cell densities, donor to recipient ratios, nutrient levels and incubation temperatures. Starved cells retained the capacity to conjugate, but plasmid transfer frequency was higher in the presence of nutrient. Above a minimum level, conjugation ability was not enhanced by nutrients. Temperature affected conjugation ability, the optimum being 20°C - 30°C. The presence of a nonconjugative strain decreased conjugation, by leading to earlier nutrient exhaustion and growth arrest which limited meetings between donor and recipient microcolonies. The model and the experimental system demonstrate the importance of spatial effects on conjugation. Description and prediction of gene transfer in natural environments will require models of greater complexity, and more sophisticated experimental testing, but this study provides a basis for theoretical descriptions of gene transfer in heterogeneous natural environments, such as soil and biofilms on solid surfaces in aquatic environments.