Thesis Format
Integrated Article
Degree
Doctor of Philosophy
Program
Microbiology and Immunology
Supervisor
McCormick, John K.
Abstract
Streptococcus pyogenes is a human-adapted pathogen that causes a variety of infections including pharyngitis and skin infections, and although this bacterium produces many virulence and host colonization factors, how S. pyogenes competes with the host microbiota is not well understood. Here we detected antimicrobial activity produced from S. pyogenes MGAS8232 that was able to prevent the growth of Micrococcus luteus. This activity was produced when cells were grown in 5% CO2 in M17 media supplemented with galactose; however, the addition of alternative sugars coupled with genome sequencing experiments revealed the antimicrobial phenotype was not related to classical bacteriocins. Ascorbic acid availability was also discovered to be important in the production of the antimicrobial phenotype. To further determine genes involved in the production of this activity, a transposon mutant library in S. pyogenes MGAS8232 was generated. The transposon screen identified the mannose phosphotransferase system (Man-PTS), a major sugar transporter in S. pyogenes, as important for the antimicrobial phenotype, which was also the secondary mutation identified in the bacteriocin-deficient (ΔspbJKMN) mutant. Additional loss-of-function transposon mutants were identified to also be involved in alternative sugar utilization. Sugar utilization profiles in all the Man-PTS mutants demonstrated that galactose, mannose, and N-acetylglucosamine utilization was impaired. In vitro RNA-seq experiments in high and low glucose concentrations further identified the Man-PTS as a glucose transporter; however, there was no transcriptional regulators or virulence factors affected with the loss of the Man-PTS. A clean deletion in the Man-PTS demonstrated defects in a mouse model of nasopharyngeal, but not in skin infection. We also developed a novel RNA isolation method of S. pyogenes-infected nasopharyngeal murine tissues. This elucidated alternative sugar import, virulence regulators and factors important during peak infection. This method also elucidated that the Man-PTS was important for the initial stages of nasal infection and not at 48 hours post-infection. Overall, the ability of S. pyogenes to utilize alternative sugars presented by glycans seems to play a role in the initial stages of acute infection and interactions with the endogenous microbial population existing in the nasopharynx.
Summary for Lay Audience
Streptococcus pyogenes causes a wide range of infections and is responsible for over 500,000 deaths per year due to invasive infections and post-infection sequelae. The most common clinical manifestation of S. pyogenes are superficial infections such as pharyngitis or impetigo. S. pyogenes can adapt to its environment through alternative sugar metabolism and in this study, we identified an antimicrobial phenotype that was not bacteriocin-related but an end-product of sugar metabolism. Evidently, the mannose phosphotransferase system (Man-PTS), a well-studied sugar transporter, was involved in the production of antimicrobial activity, and was also important for S. pyogenes to utilize alternative sugars and establish infection in the nose but not skin infection. A new RNA isolation method was used to identify the differential expression of genes related to sugar metabolism and genes involved in pathogenesis during nasopharyngeal infection in a human-transgenic mouse model. Overall, this study identified potential strategies used by S. pyogenes for interactions with the resident microbiota and identified the importance of sugar metabolism in the early stages of superficial nasal infection.
Recommended Citation
Marple, Amanda C., "Streptococcus pyogenes sugar metabolism influences antimicrobial activity and niche-specific infection" (2025). Electronic Thesis and Dissertation Repository. 10706.
https://ir.lib.uwo.ca/etd/10706
