A great deal of research has been conducted on the topic of virulence factors involved in Streptococcus pneumoniae systemic diseases. However, ocular pneumococcal infections have not been as thoroughly studied. The goal of the research presented in this dissertation was to determine the virulence of different polysaccharide capsule types in pneumococcal endophthalmitis, test protection provided by cholesterol in combination with an antibiotic in pneumococcal keratitis, and determine if protection is provided by active and passive immunization with major virulence factors in pneumococcal endophthalmitis.;The first study used four bacterial capsule mutants and a rescue strain (nonencapsulated mutant with type 4 capsule locus re-inserted) all sharing the same genetic background. These mutants were compared in a rabbit endophthalmitis model to determine differences in pathogenesis by slit-lamp examination (SLE), myeloperoxidase (MPO) assays, electroretinograms (ERGs), and bacterial counts from infected vitreous. These experiments tested the hypothesis that different capsule types of S. pneumoniae cause varying degrees of pathogenesis. It was determined that severity of infection does not correlate with prevalence of capsule type in pneumococcal endophthalmitis.;We previously showed that both capsule and pneumolysin are important virulence factors in endophthalmitis. Capsule does not play a significant role in pneumococcal keratitis. Pneumolysin, however, does. Since pneumolysin is a toxin belonging to the cholesterol-dependent cytolysin family, we hypothesized that treatment with cholesterol will aid in protecting the cornea against damage caused by pneumolysin producing strains of S. pneumoniae. Moreover, we hypothesized that addition of a topical antibiotic to the cholesterol will provide a synergistic effect in that bacterial recovery from the cornea will be reduced. These hypotheses were determined to be true by comparing SLE, MPO, and bacterial counts from infected corneas. We found that combination therapy using both cholesterol and moxifloxacin killed all bacteria in the eye and allowed for a less severe clinical infection compared to treatment with moxifloxacin alone, cholesterol alone, or PBS.;Our laboratory previously determined that active immunization with pneumolysin (ΨPLY; recombinant PLY with a point mutation leaving 1% hemolytic activity) helps protect against pneumococcal endophthalmitis. Since there is a readily available polysaccharide vaccine used to protect against pneumonia, we set forth to test the efficacy of this vaccine against pneumococcal endophthalmitis to determine if Vaccination with the polysaccharide vaccine alone or in combination with PLY would aid in protection against pneumococcal endophthalmitis. We also tested the antiserum (against polysaccharide, pneumolysin, or a mixture of the two virulence factors) to determine if passive immunization allows for protection against pneumococcal endophthalmitis. Studies have shown that a commonly available conjugate vaccine for pneumococcal pneumonia may show better protection than the previously mentioned polysaccharide vaccine, so we determined the efficacy of the conjugate vaccine as well in pneumococcal endophthalmitis. Completion of these studies involved SLE scores, ERGs, blood killing assays, MPO assays, and bacterial counts from infected vitreous. We found that both active and passive immunization with PPSV23 with and without ΨPLY significantly lowered clinical severity and percent loss of retinal function caused by pneumococcal endophthalmitis. Also, both active and passive immunization with PCV13 protected the retina significantly better than mock immunization at 24 hours PI. Through these findings, we hope to add to the understanding of virulence factors of and treatments for Streptococcus pneumoniae ocular infections.
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