Impact of Bioactive Molecules Secreted by Lactobacillus Acidophilus La-5 on Clostridium Difficile Virulence Factors
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IMPACT OF BIOACTIVE MOLECULES SECRETED BY LACTOBACILLUS ACIDOPHILUS LA-5 ON CLOSTRIDIUM DIFFICILE VIRULENCE FACTORS by Afsaneh Najarian A Thesis Presented to The University of Guelph In partial fulfilment of requirements for the degree of Doctor of Philosophy in Food Science Guelph, Ontario, Canada ©Afsaneh Najarian, November 2017 ABSTRACT IMPACT OF BIOACTIVE MOLECULES SECRETED BY LACTOBACILLUS ACIDOPHILUS LA-5 ON CLOSTRIDIUM DIFFICILE VIRULENCE FACTORS Afsaneh Najarian Advisors: University of Guelph, 2017 Dr. Mansel W. Griffiths Dr. Shayan Sharif Clostridium difficile is a leading pathogen of hospital-associated diseases including infectious diarrhea and pseudomembranous colitis. Increasing frequency and severity of diseases besides inconsistent results of antibiotic therapy, demand alternative therapeutic candidates using a different strategy to control pathogenicity of C. difficile. Unlike antibiotics, antivirulence compounds control bacterial infection without killing them or developing antibiotic-resistant. Reducing essential virulence factors in C. difficile including toxin production, adherence, and biofilm formation could substantially minimize its pathogenicity and lead to a faster recovery from the disease. This study aimed to investigate antivirulence effects of La-5 bioactive molecules produced by Lactobacillus acidophilus La-5 namely proteobiotics on the pathogenicity of C. difficile. Three clinically important strains of C. difficile (ribotypes 027, 078, and 001) were incubated with or without reconstituted La-5 cell-free supernatant (CFS). The C. difficile culture filtrates were collected for the assessment of quorum sensing, and expression of several virulence genes performing reverse transcription q-PCR. C. difficile attachment and cytotoxicity in human epithelial cells were monitored in vitro using human epithelial cells HT-29 and Caco-2 monolayers. Additionally, L. acidophilus La-5 was incubated in a medium containing whey protein, and inhibitory effects of its CFS were tested performing quantitative biofilm assay then visualized in scanning electron microscopy (SEM). Bioactive molecules caused a significant down-regulation in expression of some of the virulence genes mainly two essential toxin genes tcdA and tcdB and adhesion gene Cwp84 in all C. difficile strains. A substantial down-regulation in luxS expression was observed in ribotype 027 and 078, and 001 (P<0.05). La-5 bioactive molecules also reduced cytotoxicity and cytopathic effect of C. difficile culture filtrate on HT-29 and Caco-2 monolayers significantly (P < 0.0.5). Furthermore, pre-incubation of cell monolayers and La-5 CFS reduced attachment of the C. difficile bacterial cells on both cell monolayers. The biofilm formation and population of C. difficile cells encased in biofilms were significantly decreased within the treated cultures (P < 0.0001). SEM analysis also confirmed quantitative results showing a sufficient reduction in biofilm formation. Our study suggests that La-5 bioactive molecules provide a supportive adjunct therapy for C. difficile infection, prevent relapses, and improve disease outcome. ACKNOWLEDGMENTS First and foremost, I would like to thank Professor Mansel Griffiths sincerely. Thank you for providing me the opportunity to conduct this research under your supervision. Your expert, knowledge, and endless support encouraged me throughout my Ph.D. program. You let me challenge myself and taught me to think critically inside and outside the box. My great appreciation goes to Dr. Shayan Sharif. Without your encouragement, support and guidance this thesis would not have been completed. I am extremely grateful to you for standing by me through the ups and downs I faced during my study. I am thankful to you for being supportive and for having faith in me. Exceptional thanks to Dr. Milena Corredig. Thank you for your help and support and for being one of the great members of my advisory committee. Your expert advice and your friendship throughout my research, and trusting in my ability gave me the strength to move forward with my program. I would like to express my sincere thanks to Dr. Mitra Amiri for being my great mentor. Your advice, vast knowledge, and friendship was great inspiration for me. Especial thanks to Dr. Alexandra (Sandy) Smith for microscopy training and assisting me with the sample preparation for scanning electron microscopy. A great thank you to Dr. Scott Weese for his guidance and expert advice, and to Joyce Rousseau in Ontario Veterinary College for providing me the C. difficile strains. I would like to thank Dr. Rocio Morales for her supervision and guidance. Also, I acknowledge all the past and present students and researchers of Canadian Research Institute for Food Safety (CRIFS) for sharing ideas, excellent cooperation and making our laboratory a lively and friendly workplace. I appreciate staff and students at “Dairy Lab” in Food Science Department for welcoming attitude and for supporting me during my work there and for their excellent cooperation. I am deeply thankful to the faculty and staff in the Food Science Department for their excellent support and to the University of Guelph and financial sources that supported this project to be completed. I would like to express my most profound gratitude to my husband Mohsen and my two sons Mohammad and Matin for their unconditional love, understanding, help, and sacrifices they made for me throughout my academic journey. My sincere thanks go to my late father, and my two late brothers for inspiring me to start this path, and my huge thanks go to my beloved mother and my dear sister and brothers for sharing my problems and supporting me during our losses. Last but not least a big thanks to all of my friends for cheering me up and supporting me by having me in their thoughts and prayers. iv TABLE OF CONTENTS ABSTRACT ................................................................................................................................................ II ACKNOWLEDGMENTS ........................................................................................................................ IV TABLE OF CONTENTS .......................................................................................................................... V LIST OF ABREVIATIONS ...................................................................................................................... X LIST OF FIGURES .............................................................................................................................. XIII LIST OF TABLES ................................................................................................................................. XIV CHAPTER 1 ................................................................................................................................................ 1 GENERAL INTRODUCTION AND THESIS OBJECTIVES ............................................................... 1 CHAPTER 2 ................................................................................................................................................ 6 LITERATURE REVIEW .......................................................................................................................... 6 2. CLOSTRIDIA ......................................................................................................................................... 6 2.1 CLOSTRIDIUM DIFFICILE............................................................................................................ 7 2.1.1 Clostridium difficile Microbiology ................................................................................................. 7 2.1.2 C. difficile Infection (CDI) and C. difficile associated diseases (CDAD) ................................... 8 2.1.3 Epidemiology and Variation in Virulence Factors of C. difficile Strains: Hypervirulent Strains .................................................................................................................................................... 10 2.1.4 Disease Transmission ................................................................................................................... 12 2.1.5 History of Clostridium difficile infectious disease ...................................................................... 13 2.2 CLOSTRIDIUM DIFFICILE VIRULENCE FACTORS ............................................................. 14 2.2.1 Non-toxigenic Virulence Factors: Colonization and Adherence.............................................. 14 2.2.2 Toxigenic Virulence Factors and Mechanism of Action ........................................................... 16 2.2.3 Binary Toxins ............................................................................................................................... 22 2.3 C. DIFFICILE OTHER VIRULENCE FACTORS ...................................................................... 23 2.3.1 C. difficile Sporulation and Germination ................................................................................... 23 v 2.3.2 C. difficile Quorum Sensing......................................................................................................... 25 2.3.3 C. difficile Motility ....................................................................................................................... 28 2.3.4 C. difficile Biofilm Formation ..................................................................................................... 29 2.4 CDI