Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Microbiology and Immunology

Supervisor

Dr. David Heinrichs

Abstract

Staphylococcus aureus is an important human pathogen and crucial part of its pathogenesis depends on its ability to acquire purines to cause disease. In this study, I screened a library of individual mutants under purine import-dependent conditions by inhibiting the purine biosynthesis using the pharmacological agents methotrexate and 6-mercaptopurine and supplementing inosine monophosphate and/or guanine as an exogenous purine source. I identified an ATP-Binding Cassette transporter mutant that failed to grow under the selective purine transport conditions. Further growth characterization of the mutant revealed that the growth defect was not due to an inability to transport purines but rather to downstream effects related to the toxicity of the purine biosynthesis inhibitors. A thorough understanding of S. aureus purine acquisition will allow for development of antimicrobials with prolonged effectiveness.

Summary for Lay Audience

Staphylococcus aureus is a bacterium that usually colonizes the skin of humans but is capable of causing various invasive and life-threatening diseases. To cause disease, S. aureus requires nutrients that allow the bacterium to grow. One such type of nutrients are called purines that are building blocks of DNA and compounds used as energy by the cells. While S. aureus can make purines itself, it can also import them from the environment through transporters; however, purine transport in S. aureus has not been well characterized. This study aimed to identify a S. aureus purine transporter. This was done by using specific drugs to block the ability of the bacteria make their own purines rendering them dependent on taking up purines from the environment. I screened over 2,000 mutants and looked for specific mutants that could not grow in the presence of these drugs, indicating that they cannot take up purines, and thus, could be the mutants of our interest. Thorough understanding of how S. aureus acquire purines is essential in developing antimicrobials with prolonged effectiveness.

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