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Advisory Committee Chair

David E Briles

Advisory Committee Members

James A Coker

Marilyn J Crain

Document Type

Thesis

Date of Award

2012

Degree Name by School

Master of Science (MS) College of Arts and Sciences

Abstract

Streptococcus pneumoniae (SP) is a respiratory pathogen and leading cause of morbidity and mortality worldwide, but its role in cystic fibrosis (CF) has not been well studied. While prospectively examining the incidence of SP infection, a high number of SP were recovered from the sputum of pediatric CF patients. The predominant serotypes identified were 3, 19A, and 19F. Serotype 3 was isolated more readily in CF patients than from patients without CF (P=0.0159). All serotype 3 isolates were mucoid and produced high levels of polysaccharide capsule compared to others in the collection. Mucoid bacteria, predominately Pseudomonas aeruginosa, are commonly associated with CF respiratory decline and biofilm formation despite the use of antibiotics. It is unclear whether mucoid SP plays a significant role in biofilm development or contributes to the development of disease in CF patients. We examined the ability of mucoid and non-mucoid SP to form biofilms. Static adherence assays were used to examine initial and late adherence to polystyrene plates and primary epithelial cells. Continuous flow-cell assays were used to examine mature biofilm formation. Additionally, congenic CF-mice were infected intranasally with mucoid and non-mucoid SP. Our results indicated that serotypes 19A and 19F (non-mucoid) were more successful at initial adherence than mucoid serotype 3 isolates (P<0.05) whereas during late adherence, mucoid isolates seemed to have an advantage (P<0.05). Under our flow-cell conditions, confocal microscopy revealed that highly encapsulated mucoid type 3 SP formed denser mature biofilms than lower encapsulated mucoid type 3. However an encapsulated mucoid type 3 strain formed a less structured mature biofilm than its cps3S- acapsular non-mucoid mutant. Results of CF-mice infections suggested that mucoid type 3 SP caused more severe lung disease than non-mucoid 19A SP (P<0.01), and did so more readily in the lungs of CF-mice than in WT-mice (P=0.0196). These studies indicate that serotype, polysaccharide capsule production, and mucoidy all may play a role in the development of pneumococcal biofilms as well as in the susceptibility of CF-mice to pneumococcal lung infection. Furthermore, defects in CFTR may increase susceptibility to highly mucoid serotype 3 pneumococci.

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