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From Ideal to Real: Understanding the Role of Pathogens in the Environment


The overall goal of this investigation was to elucidate the effects the environment had on pathogenic bacteria in natural and engineered systems. Pathogens are generally studied by growing a single strain in nutrient rich media (ideal conditions), which do not accurately simulate the environments in which these bacteria are found. Thus, this project was developed to show the variations in bacterial phenotype based upon growth phase, to compare the fate and transport of 11 Escherichia coli isolates in an idealized media versus a more environmentally representative bovine manure extract, and to move away from the ideal to the real, by simulating representative environments in which pathogen proliferation can occur.

This dissertation work has allowed for the following critical observations to be made. The conditions in which bacteria are grown in the laboratory can significantly alter the cells' physical-chemical and transport properties. Specifically, the growth phase of Pseudomonas aeruginosa (PAO1) was the main influence on the relative cell surface hydrophobicity. This in turn changed the mechanism by which the cells adhered to a quart crystal microbalance with dissipation (QCM-D) sensor surface. Additionally, experiments investigating 11 E. coli isolates showed that the solution in which the cells are grown (ideal media vs. real manure extract) has a significant influence on their physical-chemical and transport properties of the bacteria. This work demonstrated the need to study pathogens in conditions that better approximate the complexity of natural systems. Thus, three in vitro systems were built to model environments (human colon, septic tank, and groundwater) in which pathogens may be found. A human fecal microbial community was inoculated in the model colon and subsequently into the septic tank and groundwater systems, which led to a change in the microbial community's structure and function. A model pathogen, E. coli O157:H7, was added to the systems and was found to significantly impact the microbes present and their resulting fate and transport. This collection of studies confirms the need to study pathogens in simulated systems that more closely represent the real environments in which the cells may proliferate.

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