Date of Award
Doctor of Philosophy (PhD)
This thesis investigates the interactions of lysogenic bacteriophage with Streptococcus pyogenes. We were specifically interested in elucidating novel ways in which the prophage influence GrAS virulence and survival either within the host cell or within the bacterial population. In turn, we also hoped to determine how the bacteria (and possibly other integrated phage) might influence prophage activity or gene expression. Our studies focused on two polylysogenized GrAS strains, a M6 serotype (MGAS10394) and a M1 serotype (SF370). In our M6 studies, we chose a streptococcal strain lysogenized by a chimeric bacteriophage element (Φ10394.4), which contains the erythromycin resistance gene mefA, in order to elucidate why genomes of certain erythromycin-resistant isolates of group A streptococci are resistant to SmaI endonuclease cleavage. In the work presented here, we identified a restriction modification system contained on the bacteriophage chimeric-element and successfully characterized the first methyltransferase (M.SpyI) encoded in S. pyogenes. In the M1 strain, allelic recombination techniques were used to begin to analyze the role and regulation of a bacteriophage-encoded potential superantigen, SpeH. Next, we designed a novel system to specifically select for the loss of integrated phages entirely from the genome. This technique allowed us to study the novel role that two SF370 phage play in regulating GrAS chromosomal genes involved in bacterial metabolism, DNA repair and mutagenesis. We were also able to begin to elucidate the effects that individual and multiple phage loss have on SF370 virulence and survival, as we successfully constructed the first strain of GrAS that is completely devoid of bacteriophages. In the course of these studies, we also manipulated lytic bacteriophage genes from two different Staphylococcus phage genomes to genetically engineer a novel chimeric endolysin (ClyS). We demonstrated the antimicrobial lytic activity of ClyS against methicillin-resistant Staphylococcus aureus (MRSA) in both in vivo colonization and septicemia models, and were also able to show its synergistic activity with oxacillin in in vitro and in vivo models. This work highlights the potential of ClyS as a novel therapeutic agent for the treatment of MRSA and other staphylococcal infections.
Euler, Chad W., "The Role of Lysogenic Bacteriophage in Virulence and Survival of Streptococcus Pyogenes" (2010). Student Theses and Dissertations. 260.