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THE ROLE OF QUORUM SENSING IN SURVIVAL, BIOFILM FORMATION AND GENE EXPRESSION OF LISTERIA MONOCYTOGENES

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Title: THE ROLE OF QUORUM SENSING IN SURVIVAL, BIOFILM FORMATION AND GENE EXPRESSION OF LISTERIA MONOCYTOGENES
Author: Ali, Saleh
Department: Department of Food Science
Program: Food Science
Advisor: Griffiths, Mansel
Abstract: In recent years, listeriosis, the disease caused by Listeria monocytogenes has gained importance because of the increasing number of listeriosis outbreaks. Frequent reports of morbidity and mortality cases linked to infection by L. monocytogenes have concerned the food industry, and thus, the control of L. monocytogenes is a great challenge faced by the food industry. The discovery of the quorum-sensing system in bacteria and its role in cell behavior has made it a target for microbiologists to understand bacterial behavior and adaptation. The aim of the present study was to investigate the role of quorum sensing on the physiology, survival, and virulence in L. monocytogenes. In this study, the presence of quorum-sensing systems luxS and agrD in L. monocytogenes was investigated. Both systems were found to exist in L. monocytogenes and other Listeria species, suggesting a possible role of quorum sensing in this bacterium. In addition, the production of auto-inducers and the effect of environmental stress on auto-inducers production were examined. Different environment parameters appeared to have an impact on the production of quorum-sensing signaling molecules. To obtain a better understanding of the possible role of quorum sensing in L. monocytogenes, a whole-genome microarray assay was performed using the L. monocytogenes wild-type strain against 2 mutant strains—agrD mutant and luxS mutant strains. Down- and upregulation of genes representing different functions in the cell were observed in both quorum-sensing systems at both refrigeration and optimum temperatures. Some of the important virulence genes were differentially expressed in the agrD mutant, suggesting a possible role of agrD quorum sensing in virulence of this pathogenic bacteria. The role of quorum sensing in survival and biofilm formation was subsequently investigated. Quorum sensing was found to have an impact on survival under different stress conditions, suggesting possible indirect support rather than direct control of survival and biofilm formation. Biofilm formation examined by confocal laser scanning microscopy revealed a significant difference in the formation of biofilms between wild- type, agrD, and luxS mutant strains. Thus, new insights into the role of cellular signaling mechanisms may throw light on novel mechanisms, which could be applied to control this problematic bacterium.
URI: http://hdl.handle.net/10214/3207
Date: 2011-12


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http://creativecommons.org/licenses/by-nc-nd/2.5/ca/ Except where otherwise noted, this item's license is described as http://creativecommons.org/licenses/by-nc-nd/2.5/ca/