Date of Award

12-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Program

Biomedical Sciences

Track

Microbial Pathogenesis, Immunology, and Inflammation

Research Advisor

Mark A. Miller, Ph.D.

Committee

Yan Cui, Ph.D. Elizabeth A. Fitzpatrick, Ph.D. Tony N. Marion, Ph.D. Robert Williams, Ph.D.

Abstract

Burkholderia pseudomallei (Bp) is a saprophytic, gram-negative aerobe and the causative agent of the disease melioidosis. Melioidosis is an infectious disease that occurs in humans and animals and is prevalent in Southeast Asia, northern Australia and other tropical areas. Transmission occurs through direct contact with the organism via ingestion, inhalation, or through open wounds and skin abrasions. Clinical presentation is extremely variable and can range from acute septicemia with bacterial dissemination to distant sites, to an isolated pulmonary infection. Treatment of melioidosis can be problematic because it is often difficult to diagnose and Bp is resistant to a diverse group of antibiotics. Even with treatment, the mortality rate of melioidosis is 20 to 50%.

While this pathogen is not widespread in the United States, it is a significant U.S. health issue because of its high potential for use as a biological weapon. The US Centers for Disease Control and Prevention (CDC) and The Department of Health and Human Services (DHHS) has recognized Bp as a Tier 1 Select Agent, meaning there is no effective vaccine against this high morbidity/mortality disease. Furthermore, according the CDC, other factors including aerosol infectivity, the severity of infection, and the global distribution of this pathogen makes it a potential bioterrorism agent that poses a threat to national security, if intentionally released into populated areas.

There has been little investigation into the role of host genetic background as it relates to susceptibility and/or resistance to Bp infection. It has been known for some time that inbred and recombinant inbred mice exhibit differences in susceptibility to many intracellular pathogens and are thought to provide excellent models for acute and chronic human melioidosis. Therefore, this project set out to identify host genetic elements that contribute to differential immune responsiveness and/or susceptibility to a Bp infection using a murine pneumonic challenge model. There is a high potential for discovery of host genes/genetic networks that confer resistance or sensitivity to this dangerous and emerging pathogen using inbred and BXD mouse strains as an in vivo modeling system of melioidosis.

We have utilized recombinant inbred BXD mice and a powerful array of complementary computer-based modeling algorithms and databases collectively known as GeneNetwork. We infected parental mice and 32 BXD strains with 50-100 CFU of Bp (strain 1026b) and monitored survival and weight retention each day over an eleven-day time course. Initial studies revealed that Bp infection elicits phenotypically distinct innate immune responses in terms of survival and weight loss following pneumonic infection in parental and BXD mice. Using the computational tools in GeneNetwork, we performed genome-wide linkage analysis of our survival and weight loss phenotypic data to identify that survival is a complex trait involving loci on chromosomes 5 and 7 and weight retention involves loci on chromosome 12. We then analyzed and ranked several potential candidate genes within the significant and/or suggestive interval on these chromosomes that appear to correlate with differential susceptibility to Bp infection. Several genes have intriguing connections with innate immunity, regulation of Nf-kβ, apoptosis, cell cycle regulation, nervous system development, calcium homeostasis, lipid transport, host cell growth and development, and autophagy.

To date, there have been few published studies that have identified specific host genetic elements that correlate with resistance and/or susceptibility to the acute form of melioidosis. Therefore, the identification of key host genetic factors that control resistance or susceptibility to Bp is of much importance. Results generated from this work will increase our understanding of the interactions between Bp and its genetically diverse hosts, which will enhance the understanding of Bp pathogenesis and increase the biological knowledge to help guide the progression and development of preventative and therapeutic measures to a Bp infection as well as other high morbidity/mortality respiratory pathogens.

DOI

10.21007/etd.cghs.2015.0084

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