Date of Award
2024
Degree Type
Thesis
Degree Name
Master of Science in Biological and Environmental Sciences (MSBES)
Specialization
Cell and Molecular Biology
Department
Cell & Molecular Biology
First Advisor
Matthew Ramsey
Abstract
Around 50% of the United States adult population suffers from some form of periodontal disease. From gingivitis to severe periodontitis, periodontal disease is associated with a plethora of chronic and systemic diseases, like rheumatoid arthritis, cardiovascular disease, type-two diabetes, and Alzheimer's disease. Prevention of periodontitis relies on the establishment and maintenance of a resilient, eubiotic oral microbiome. A key member of the healthy oral microbiome is Haemophilus parainfluenzae (Hp). Hp is a highly prevalent and abundant oral generalist. As a health-associated commensal, understanding its relationships within the microbial community and its interactions with the host may shed light on what is required for a healthy, resilient oral microbiome to thrive. One way that Hp interacts with the host is through the host's immune responses. Hp is exposed to phagocytic immune cells like neutrophils and macrophages when living below the gumline as part of the subgingival plaque. As part of the subgingival and supragingival plaque, Hp comes into contact with gingival crevicular fluid (GCF), a serum-like exudate containing the complement system. Previous work in the M. Ramsey lab has shown that Hp is highly resistant to phagocytosis and complement-mediated killing. These high levels of immune evasion are inconsistent with the very low incidences of infection or invasive disease caused by Hp, and the observation that the abundance of Hp is negatively correlated with inflammation in the mouth. Additionally, the mechanism(s) of resistance to killing by the immune system is unknown. To address this knowledge gap, highly saturated mariner transposon sequencing (TnSeq) libraries were created to identify conditionally essential genes in two strains of Hp, the type strain, ATCC33392, and a novel oral isolate, EL1, for survival in 50% normal human serum. Gene deletion mutants were created for conditionally essential genes in each strain that were identified as potentially conferring serum sensitivity. These mutants had their serum survival phenotypes and lipopolysaccharide structure characterized to identify mechanisms of complement resistance. Our results demonstrate that Hp does not rely solely on one mechanism to evade complement but has an assortment of tools to survive exposure to complement, from lipopolysaccharide to complement regulator-binding surface proteins.
Recommended Citation
McPartland, Morgan J., "INVESTIGATION OF SERUM RESISTANCE IN HAEMOPHILUS PARAINFLUENZAE" (2024). Open Access Master's Theses. Paper 2512.
https://digitalcommons.uri.edu/theses/2512