Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Wang, Chinling

Committee Member

Donaldson, Janet R.

Committee Member

Seo, Keun Seok

Committee Member

Hanson, Larry A.

Committee Member

Nannapaneni, Ramakrishna

Date of Degree

1-1-2012

Document Type

Dissertation - Open Access

Degree Name

Doctor of Philosophy

College

College of Veterinary Medicine

Abstract

The rates of the US hospitalization and mortality caused by Listeria monocytogenes was estimated to be the highest of 31 food-borne pathogens including Salmonella, Escherichia coli, Campylobacter, and Clostridium. This pathogen has an ability to survive under extreme conditions widely found in the natural environment and food. Among 13 serovars L. monocytogenes serovar 4b, 1/2a and 1/2b are mainly associated with human listeriosis outbreaks. The deadliest outbreaks of human listeriosis and massive product recalls in multi-states were associated with ready-to-eat (RTE) food products such as mexican-style cheese, turkey deli meat, cabbage, and cantaloupes contaminated with the bacterium. Thus, contamination of food products with L. monocytogenes is a major concern for the food industry, regulatory agents and consumers. This study used oligonucleotide probe-based DNA array, quantitative real time RT-PCR, gene manipulation, biochemical assays, and electron microscopy techniques to better understand the molecular mechanisms of L. monocytogenes under stress conditions on various food matrices,. The transcriptome profiles of L. monocytogenes via microarray analysis and quantitative PCR identified genes that are involved in adaptation, attachment, or survival and growth of the pathogen under a stress condition on a food matrix. The mechanistic and functional studies further characterized the biological properties of L. monocytogenes in various RTE food products. We showed that specific genes involved in energy metabolism, biosynthesis of proteins, and cellular processes to affect listerial growth or adaptation to a RTE meat matrix were changed with no associated changes in virulence factor expression. We also reported that the effects of salt stress on the expression of genes involved in PTS and its related metabolic enzymes in L. monocytogenes. In addition, a novel gene involved in attachment to RTE vegetables and fruits was discovered. The concern about the prevalence of L. monocytogenes in RTE food has been escalated by recent food-borne outbreaks, suggesting that the prevention of human listeriosis become the top priority for the food industry. Data from these studies help us to better understand the survival, growth and contamination of the bacterium under different conditions. The information will help the development of prevention strategies in RTE meat products, vegetables and fruits.

URI

https://hdl.handle.net/11668/18309

Comments

attachment||PTS||gene expression||stress||listeria

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