Wednesday, December 22, 2010

DISSERTATION: Inactivation Mechanisms of Alternative Food Processes on Escherichia coli O157:H7

ABSTRACT: Application of high pressure (HP) in food processing results in a high quality and safe product with minimal impact on its nutritional and organoleptic attributes. This novel technology is currently being utilized within the food industry and much research is being conducted to optimize the technology while confirming its efficacy.

Escherichia coli O157:H7 is a well studied foodborne pathogen capable of causing diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome. The importance of eliminating E. coli O157:H7 from food systems, especially considering its high degree of virulence and resistance to environmental stresses, substantiates the need to understand the physiological resistance of this foodborne pathogen to emerging food preservation methods. The purpose of this study is to elucidate the physiological mechanisms of  processing resistance of E. coli O157:H7. Therefore, resistance of E. coli to HP and other alternative food processing technologies, such as pulsed electric field, gamma radiation, ultraviolet radiation, antibiotics, and combination treatments involving foodgrade additives, were studied. Inactivation mechanisms were investigated using molecular biology techniques including DNA microarrays and knockout mutants, and quantitative viability assessment methods.

The results of this research highlighted the importance of one of the most speculated concepts in microbial inactivation mechanisms, the disruption of intracellular redox homeostasis. Groups of genes involved in redox homeostasis or protection against oxidative stress, such as thiol-disulfide redox systems, Fe-S cluster assembly proteins, stress related DNA binding proteins, sigma factors, and other miscellaneous genes were found involved in the mechanism of inactivation of E. coli by HP and combinations of HP and tert-butylhydroquinone. The origin or phage content of E. coli O157 exhibited a correlation to processing resistance. Lastly, multiple rounds of HP treatments subsequently protected E. coli O157:H7 against a variety of deleterious factors, demonstrating adaptability of the pathogen to stress. The results of this research will provide food processors the knowledge necessary to optimize processing conditions in order to produce a safe food product, devoid of E. coli O157:H7.
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