Date of Award
Open Access Dissertation
Richard A Long
The ability of opportunistic enteric pathogens to cause disease is effected by their ability to survive the variable and lethal acidity of the mammalian host gastrointestinal milieu. In many of these pathogens, survival is conferred by an acid stress response (ASR). ASR is elicited when bacterial cells are pre-conditioned in sub-lethal acidity (pH 4-6) which induces rapid biochemical and physiological modifications and facilitates survival when extreme acidity (pH 1-3) is encountered. In Vibrio cholerae, the causative agent of the diarrheal disease Cholera, ASR was initially investigated in an effort to determine how this ubiquitous aquatic bacterium is capable of causing disease on pandemic scales. It has since been discovered that V. cholerae is capable of a robust ASR. However, the conservation of this response among clinical and environmental V. cholerae populations has been unexplored. Further, the environmental elicitation of ASR in V. cholerae has not been considered. This dissertation examines ASR capabilities among V. cholerae populations from clinical and environmental isolation origins. Using the molecular approach, polymerase chain reaction (PCR), nearly fifty V. cholerae isolates were screened to establish presence/absence of a subset of genes involved in ASR. A high-throughput technique developed during this dissertation (Chapter 3) was used to evaluate the ability of these isolates to respond to lethal acid stress. ASR positive phenotypes were identified among clinical and environmental V. cholerae populations (Chapter 4) and this response was not genotype dependent. In silico analysis of Vibrio genomes reveals that clinical V. cholerae genomes and genomes isolated from Cholera endemic regions, display greater sequence similarity of ASR genes than do environmentally derived genomes. The growth of V. cholerae in moderately acidic freshwater systems has important ecological implications but remains poorly characterized. We examine the population growth dynamics and elicitation of ASR in the clinical V. cholerae N16961 strain cultured in environmental swamp water (Chapter 5). Our results suggest this opportunistic pathogen is capable of prolonged growth in swamp water samples at densities above the known minimum infectious dose. Further, cultivation in the swamp water was shown to elicit ASR which facilitated survival of V. cholerae N16961 upon exposure to extreme acidity. ASR elicitation was supported by the observation of ASR gene expression profiles similar to previous findings. Finally, the ASR of culturable, heterotrophic bacterial communities from estuarine, freshwater and contaminated sediments is evaluated (Chapter 6). Sediment associated bacterial communities isolated from euphotic and anoxic partitions displayed a robust response to extreme acidity. Sediments contaminated with copper and mixed polyaromatic hydrocarbons (PAHs) were shown to select for bacterial communities capable of ASR. The findings of this dissertation research may be valuable in the development and improvement of tools predicting environmental pathogen distribution and will benefit efforts towards disease mitigation and prevention.
Swenson, G. J.(2013). Environmental Pre-Conditioning of Bacterial Populations and Communities to Extreme Acidity. (Doctoral dissertation). Retrieved from http://scholarcommons.sc.edu/etd/2362