Date of Graduation
Davis College of Agriculture, Natural Resources and Design
Bacteria are constantly being exposed to changing conditions in the environment. Exposure to adverse conditions such as pH, temperature, and desiccation may cause stress to the bacteria, potentially resulting in loss of viability and growth. Cronobacter sakazakii and Escherichia coli were exposed to cold temperature (4°C) and room temperature (24°C) nutrient-limiting groundwater. As a function of time (0 to 15 days), samples were removed from the stress and analyzed. Response of stressed cells was evaluated by three approaches: (i) traditional viable cell counts (nonselective and selective media), (ii) substrate utilization patterns (BIOLOG GN microplates), and (iii) antibiotic resistance patterns (modified Kirby-Bauer disk diffusion assay). The cold, nutrient-limiting environment resulted in physical changes as reflected by survival and sublethal injury, changes in metabolic activity as reflected by differences in utilization of carbon substrates, and changes in antibiotic resistance patterns as reflected by increased resistance or susceptibility to six antibiotics. Three major findings were observed. First, analyses of the survival/injury data indicated C. sakazakii was more tolerant to extended ground water exposure than E. coli, regardless of water temperature. Second, changes in substrate utilization patterns (BIOLOG profiles) for both organisms as a result of stress present an option in which recovery media could be altered or supplemented in order to enhance detection of stressed cells from low-temperature aquatic environments. Finally, changes in antibiotic resistance patterns due to cold temperature stress may also have implications regarding detection of stressed cells, as well as the efficacy of clinical use of certain antibiotics to treat infectious disease. Findings from this research should provide a better understanding of the physiological response of C. sakazakii and E. coli to low temperature aquatic environments.
Dailey, Alisha L., "Survival, injury, and antibiotic resistance patterns of Cronobacter sakazakii and Escherichia coli resulting from exposure to low-temperature ground water" (2013). Graduate Theses, Dissertations, and Problem Reports. 7308.