Electronic Thesis and Dissertation Repository

Thesis Format



Master of Science


Microbiology and Immunology


Heinrichs, David E.


Staphylococcus aureus and its small colony variants (SCVs) are commonly isolated from the lungs of cystic fibrosis (CF) patients. Although studies have suggested that cystic fibrosis transmembrane regulator (CFTR)-deficient macrophages are diminished in their ability to kill intracellular pathogens, whether this is true for CFTR-deficient macrophages infected with S. aureus or its SCVs is unknown. I employed gentamicin protection and eFluorÔ-670-based proliferation assays to assess the intracellular replication of S. aureus in CFTR inhibitor treated THP-1 and primary human macrophages, and in primary macrophages derived from CF patient blood. My work shows that the susceptibility of CFTR-deficient macrophages to the intracellular growth of wildtype S. aureus USA300 and its SCVs is similar to control macrophages. Importantly, my work demonstrates that SCVs proliferate intracellularly, suggesting that they overcome their auxotrophy through an unknown mechanism. Due to the increasing prevalence of antibiotic-resistant S. aureus, a better understanding of pathogen-host interactions is vital.

Summary for Lay Audience

Staphylococcus aureus is a human bacterial pathogen that is frequently isolated from the lungs of cystic fibrosis (CF) patients. S. aureus’ multi-drug resistance complicates the treatment of CF patients who are repeatedly infected. Additionally, small colony variants (SCVs) of S. aureus which are slow-growing forms of the bacterium, are found in the CF lung and are said to result in prolonged and recurrent infection. S. aureus infections can result in lung dysfunction, which is the most common cause of morbidity and mortality in CF patients. Although patient lungs are typically highly inflamed and populated by white blood cells, these white blood cells are not able to control the presence of S. aureus. I investigated whether CF patient macrophages, an important type of white blood cell involved with the removal of pathogens, are less capable of killing this bacterium when compared to healthy macrophages, and whether SCVs differ from wildtype S. aureus in how they interact with macrophages. My work showed that in a subset of CF model macrophage populations, S. aureus and its SCVs are capable of surviving and replicating inside macrophages, as they do in healthy macrophage populations. These observations are important because they suggest that CF macrophages are not especially susceptible to infection by S. aureus. Interestingly, my findings demonstrate that SCVs can replicate inside macrophages despite being unable to produce the nutrients they require for growth, suggesting that they acquire the energy required for their growth through an unknown mechanism. This work enhances our understanding of the host-staphylococcal interactions which may occur in the context of CF and is therefore important for the discovery of novel treatments for staphylococcal infections in CF patients.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.