[The Role of Quorum Sensing In Physiology, Virulence and Gene Expression of Listeria Monocytogenes]

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ACKNOWLEDGEMENT

I would take this opportunity to thank my research supervisor, family and friends for their support and guidance without which this research would not have been possible.



DECLARATION

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Table of Contents

ACKNOWLEDGEMENTII

DECLARATIONIII

CHAPTER 02: LITERATURE REVIEW1

2.1.Research Introduction1

2.2.Food-Borne Pathogenic Bacteria2

2.2.1.Listeria.2

2.2.1.1.Background2

2.2.1.2.Genetic Diversity3

2.2.2.Listeria monocytogenes5

2.2.3.Listeriosis6

2.2.3.1.Background6

2.2.3.2.Pathogenesis8

2.3.Biofilm formation and Resistance12

2.4.Sources Of Infection14

2.5.Incidence Of Listeriosis18

2.6.Current Methods For Control Of Listeria Monocytogenes In Food19

2.7.Quorum Sensing (QS)21

2.8.Quorum-Sensing In Gram-Negative Bacteria23

2.9.Quorum-Sensing In Gram-Positive Bacteria25

2.10.Auto Inducers Production28

2.11.Listeria Monocytogenes QS31

2.12.Research Objectives32

2.13.Proceeding Chapters Overview33

REFERENCES35

CHAPTER 02: LITERATURE REVIEW

Research Introduction

Recently, high concern has been given to the increased number of food borne outbreaks worldwide. The application of Hazarad Analysis Critical Control Point (HACCP) and Good Manufacturing Process (GMP) as well as restricted policies to control food borne illnesses helped to reduce the amount of outbreaks but was unable to eradicate them. The ability of pathogens to survive and or grow under processing and storage conditions, as well as the developments of resistance and virulence expression made it even more complicated to control them in food. Pasteurization, modified atmospheric packaging, UV light treatment and many other techniques were applied to control those pathogens. The need to understand bacterial behavior and virulence becomes important to enhance food control, as understanding bacterial physiology and behavior is a key to control it. In the last decade, much attention has been focused on the bacterial cell-to-cell communication process called Quorum Sensing (QS). It was first discovered in the marine bacteria Vibrio fischeri and Vibrio harveyi and later in many gram positive and gram negative bacteria. Studies showed that chemical signaling molecules (Auto-Inducer (AI) molecules) and small peptide produced by bacteria and encoded by the luxS gene and/or agr gene play roles in survival, virulence gene expression and behavior of microorganisms.

However, much work still needs to be done fully understand the function of these signaling compounds in bacteria. Foodborne pathogens, such as pathogenic Escherichia coli, Salmonella enterica, Campylobacter and Listeria, are a major food safety issues within the industry. Among the six species of the genus Listeria, only two are pathogenic, Listeria monocytogenes that cause listeriosis and Listeria ivanovii. Listeria monocytogenes are a gram-positive pathogen that causes serious illnesses to humans and animals. It is a ubiquitous organism and thus, can be found in many foods and can survive and grow in different environmental conditions. It was found to produce AI-2 and small peptides as signaling molecules by two QS systems luxS and Agr. Thus, studying the role of QS in Listeria monocytogenes may allow us to better understand the behavior of the pathogen and may provide the key to control Listeria monocytogenes in food and food processing environments.

Food-Borne Pathogenic Bacteria

Several types of microorganisms play major roles in the food ...