Browsing by Author "Marais, Susara"

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    Characterization of the early stages in biofilm development
    (Stellenbosch : Stellenbosch University, 2004-04) Marais, Susara; Wolfaardt, Gideon M.; Bessarabov, D. G.; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Complex biofilm communities have extensively been studied in the past. Less work has been done on the early stages of biofilm formation. This study aimed to assess initial colonization patterns of biofilms on different surfaces and under different environmental conditions with application of novel methods describing biofilm surface profiles. Biofilms were cultivated on glass, polyvinylchloride (PVC) and polished stainless steel. Results from microscopy, followed by mathematical analysis and contact angle measurements proved that glass was the most appropriate substrate for this study. More extensive extracellular polymeric substances (EPS) production and apparently less cell attachment were observed on PVC and polished stainless steel surfaces. Two different series of experiments were conducted where biofilms were cultivated on the glass. Biofilm morphology was analysed under various conditions of temperature and nutrient concentration. Different temperature conditions were 8°C, 22°C and 37°C and different nutrient concentrations were 0.1%, 1% and 10% Tryptic Soy Broth (TSB). After obtaining samples after 1, 2, 3 and 4 days respectively, the biofilm surfaces were visualised using atomic force microscopy (AFM) and epifluorescence microscopy. Less cell attachment was displayed at lower temperatures and nutrient limitations. The roughness profile of the early stages of biofilm development was explored by the novel application of various existing statistical methods. Benoit software was applied for the statistical analysis of various data sets obtained from AFM imaging, using power spectrum, variogram and wavelet methods to determine the Hurst exponent. The variogram method proved to be the most suitable to describe biofilm surface profiles with consistent values of ± 0.9, indicating that biofilm growth behaviour will continue in a similar pattern. Fractal dimension values of images obtained from epifluorescence microscopy was determined by the box dimension method. The values described the self-affine patterns displayed by biofilms. Using the results of these investigations, a series of models concerning the initial stages of biofilm formation was compared to describe the development of colony patterns. This study showed that the AFM and epifluorescence microscopy can be used as analytical tools for raw data assembly. It also demonstrated a novel application of existing statistical methods in order to describe the early stages of biofilm formation. Using this approach it was shown that the early stages of biofilm formation display certain colony patterns that can be described and predicted. Such information may be used in efforts to control biofilm formation.