Browsing Theses and Dissertations by Subject "Virulence"
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Generation of Diversity During the Survival of Streptococcus pyogenesStreptococcus pyogenes is a human-specific pathogen that can cause a wide variety of diseases. These diseases range from the relatively mild pharyngitis and impetigo to invasive diseases such as necrotizing fasciitis to post-streptococcal sequelae such as rheumatic heart disease. The bacteria are frequently carried asymptomatically and may cause recurrent disease. Corresponding with their etiologic variation amongst diseases, clinical isolates demonstrate diverse virulence factor expression and random genetic mutations. In these studies, we examine the role of intracellular residence during survival as a niche for the diversification of S. pyogenes. Survival was previously studied using two in vitro systems: long-term stationary phase survival in culture and survival within epithelial cells in the presence of extracellular antibiotics. The surviving populations diversified, giving rise to stable strains with alternate colony morphologies, distinct proteomes, and altered metabolic properties. Further analysis in these studies showed that alterations in colony morphology were not solely observed during survival, but could also be induced in models mimicking acute infection. However, diversification in certain metabolic pathways occurred only during survival, and this metabolic diversification was observed at the transcriptional level. Further, one of three clinical isolates from patients with recurrent pharyngitis was altered in its metabolic profile, suggesting metabolic diversification may be occurring in vivo. The survivor strains had varied transcriptional changes in the genes encoding the virulence factors emm, slo, and speB. All of the stationary phase-derived survivor strains and two intracellular survival-derived strains had attenuated virulence in zebrafish. Most of the attenuated strains disseminated to the spleen and were cleared within three days. A whole blood killing assay showed a strong correlation between bacterial killing and emm expression. While the diversification appeared random, these strains retained their multilocus sequence type (MLST). These results suggest S. pyogenes strains with the same MLST, but diverse virulence properties, may arise during survival in the host.