Date of Award

5-2008

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Food Science and Technology

Major Professor

David A. Golden

Committee Members

Doris D’Souza, P. Michael Davidson, Arnold Saxton

Abstract

Advances in microbial genetics have allowed discovery and assignment of function for many genes. High-throughput transcription analysis can be conducted for foodborne pathogens to give insight into mechanisms of adaptation and survival in adverse conditions. With heightened knowledge of gene expression in these conditions, steps can be taken to counteract adaptive mechanisms and inhibit growth or survival of foodborne pathogens.

Sodium benzoate is a food antimicrobial that is commonly used in beverages and fruit juices. A study was conducted to determine the gene expression of Escherichia coli O157:H7 when exposed to sodium benzoate.

First, a qualitative study to determine transcription of marA, stx1, and eaeA was undertaken using real-time reverse transcriptase polymerase chain reaction (rt-RT-PCR). Expression of the mar operon causes increased antimicrobial resistance in bacterial pathogens. Shiga toxin 1 (Stx1) is a well described verotoxin produced by enterohemorrhagic E. coli (EHEC), and EaeA, or intimin, helps establish E. coli O157:H7 in the intestinal tract. For marA and stx1, rt-RT-PCR products were detected at a 1-log greater dilution in sodium benzoate treated cells, indicating a greater level of transcription in these cells.

Next, a microarray study was conducted to determine transcription of E. coli O157:H7 when exposed to 0.5% sodium benzoate. Results indicate that the phosphate specific transport (Pst) system was rapidly (within 5 min) up-regulated in response to sodium benzoate. This system is essential for supplying phosphate used in synthesizing compounds such as ATP, phospholipids, and proteins. Research with Mycobacterium smegmatis also shows that this system can serve as an efflux pump.

The urease operon was also shown to be up-regulated in E. coli O157:H7 after 60 min of exposure to sodium benzoate. Urease catalyzes the hydrolysis of urea to ammonia and carbon dioxide, and is one mechanism by which microorganisms survive in acidic environments. In this study, exposure of E. coli O157:H7 to sodium benzoate at neutral pH showed increase in transcription of the entire urease operon.

These data indicate that stx1 and marA genes as well as the Pst system and urease operon could play a role in pathogen virulence and survival when treated with sodium benzoate.

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