Respiratory Pathogen Interactions with the Microbiome: The Molecular Mechanisms to the Ethical Implications
Open Access
- Author:
- Weyrich, Laura Susan
- Graduate Program:
- Biochemistry, Microbiology, and Molecular Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 20, 2012
- Committee Members:
- Eric Thomas Harvill, Dissertation Advisor/Co-Advisor
Eric Thomas Harvill, Committee Chair/Co-Chair
Jean Elnora Brenchley, Committee Member
Jesse Ballenger, Special Member
Robert Paulson, Committee Member
Richard John Frisque, Committee Member - Keywords:
- microflora
Bordetella
respiratory tract
pathogens
COPD
microbiome
whooping cough
probiotics
Type VI Secretion System - Abstract:
- This work explores how interactions between the respiratory tract microbiome and common pathogens may contribute to pathogenesis and interrogates the ethical implications associated with such research. Three closely related, widespread respiratory pathogens, Bordetella bronchiseptica, Bordetella pertussis, and Bordetella parapertussis, were implemented to understand how pathogens can utilize classical virulence factors to overcome host flora, and, conversely, how microflora can be utilized to prevent pathogen colonization. After initially characterizing a locus in B. bronchiseptica predicted to mediate bacterial competition in vitro, the Type VI Secretion System (T6SS), we created a non-functional T6SS mutant to investigate how this pathogen uses this secretion system to initially induce pathology, modulate the immune response, and persist in the respiratory tract. The mechanism underlying persistence was later investigated; the T6SS is capable of modulating lipid antigen presentation and NK T cell accumulation at the site of infection, causing deleterious downstream effects on antibody production. Interestingly, although this secretion system has significant effects on the host and the immune response, the T6SS was also shown to mediate bacterial competition in our natural infection system. B. bronchiseptica requires a function T6SS, a Type III Secretion System, and the master regulatory system, BvgAS, to displace nasal cavity microflora organisms in vivo and out-compete host organisms in vitro. We also determined that bacterial competition within the respiratory tract can be immune-mediated; cytotoxic T-cells and IL-17, which can additionally cause the release of antimicrobial compounds, are also required to displace nasal cavity flora in vivo. Interestingly, cytotoxic T cell-mediated microflora displacement was shown to be an essential mechanism for initial colonization. In stark contrast, the human restricted pathogen, B. pertussis, did not displace murine host flora, and single host organisms were capable of blocking B. pertussis colonization. Furthermore, mice that had been antibiotic treated, and therefore were lacking normal microflora, were shown to be more susceptible to B. pertussis infection. As a first step to understanding how the T6SS is regulated and therefore understanding when this factor is utilized by these pathogens, we discovered small RNA regulatory molecules that target a putative T6SS effector. Lastly, to correlate our murine research to humans, we used metagenomic sequencing to identify bacterial flora in the lower respiratory tract of healthy humans, as well as patients with Chronic Obstructive Pulmonary Disease and asthma, to understand how the microbiome can contribute to health and disease. Finally, the ethical implications of this experimental research were examined, in terms of identifying the best method for teaching effective ethical training during graduate research and, secondly, determining the ethical and legal implications of patenting human isolated microbes. Together, this dissertation examines both the molecular interactions between pathogens, the microflora, and the respiratory tract and investigates the ethical issues generated from this research.