Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Microbiology and Immunology

Supervisor

McCormick, John K.

Abstract

Streptococcus pyogenes is a human-specific pathogen that uses a variety of adhesion molecules in order to initiate pharyngeal infection and maintain colonization. One genomic locus that is believed to contribute to adherence is the fibronectin-binding, collagen-binding, T-antigen (FCT) region, primarily due to the inclusion of genes that encode for a pilus (tee18.1), collagen-binding protein (cpa), and fibronectin-binding protein (prtF2). The precise role of these genes and the FCT region as a whole, however, have yet to be elucidated within the context of pharyngeal infection. In this study, we utilize the M18 serotype S. pyogenes strain MGAS8232 to demonstrate that the presence of the FCT region is critical in binding collagen type IV and fibronectin, and is additionally required for invasion into human pharyngeal cells, despite not impacting adherence to these cells. Furthermore, using a murine nasopharyngeal infection model, we determine that only cpa is expressed in vivo, and that removal of the FCT region does not impede the bacteria’s ability to establish infection. Overall, this study demonstrates that the FCT region is not involved during acute nasopharyngeal infection by S. pyogenes MGAS8232 but may contribute to the pathogenic life cycle through other mechanisms.

Summary for Lay Audience

Streptococcus pyogenes is a human-specific bacterium that can cause a multitude of diseases with outcomes that range from mild to fatal. Streptococcal pharyngitis, or more commonly known as ‘strep throat’, is one of these diseases and affects more than 600 million people annually. Although this disease can be self-limiting or treated with antibiotics, the persistence or recurrence of pharyngeal infection can result in more harmful complications, such as rheumatic heart disease, which can be fatal in severe cases. As such, it is critical to understand the initial infectious state of S. pyogenes. A crucial step during its pharyngeal infection is the adhesion to host tissue, which occurs through a variety of molecules that are often attached to the bacteria’s surface. One particular genomic locus implicated in adhesion is the fibronectin-binding, collagen-binding, T-antigen (FCT) region, which notably encodes a pilus structure (tee18.1), a collagen-binding protein (cpa), and a fibronectin-binding protein (prtF2). In this study we remove this region from the bacteria’s genome and assess the adherence capabilities of this mutant to several components found at the site of infection, including collagen type IV, fibronectin, and human pharyngeal cells and demonstrated that the FCT region is required to bind collagen type IV and fibronectin, but not the pharyngeal cells. Interestingly, we discovered that the ability to invade pharyngeal cells, which may lead to more detrimental diseases, is entirely reliant on the FCT region. In addition, we quantify the expression of tee18.1, cpa, and prtF2 in mice that have been infected with S. pyogenes and determined that only cpa was expressed. Furthermore, using the same mouse nasopharyngeal infection model, we demonstrated that removal of the FCT region does not impede the bacteria’s ability to establish infection. This study demonstrates that the FCT region is not involved during acute nasopharyngeal infection by S. pyogenes but may contribute to the pathogenic life cycle through other mechanisms. Overall, comprehensively evaluating the life cycle of S. pyogenes can provide insight on how to combat this globally-prevalent pathogen.

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