Phillip S. Coburn

Phillip Coburn has a broad background in microbiology and molecular biology, with specific training and expertise in bacterial genetics, mechanisms of action of bacterial protein toxins, bacterial gene regulation, and a wide range of murine infection models. His graduate training primarily consisted of characterizing a broad-spectrum, two-component toxin, termed cytolysin, that is produced by virulent strains of Enterococcus faecalis. The E. faecalis cytolysin is a unique, two-peptide lytic toxin that has evolved multiple activities in a single system.

Coburn’s most important contribution during this period was the description of the role of the larger of the two peptides, CylLL”, in the regulation of cytolysin expression. This peptide is used by E. faecalis as a means for detecting target cells in the vicinity of the bacterium and triggering high-level cytolysin expression only when target cells are present. This seminal study was published in the journal Science (1). In addition, he examined the structure/activity relationships of the CylLS” subunit by alanine scanning mutagenesis. He found that no amino acid within the mature sequence of CylLS” was dispensable for all activities. However, he did demonstrate that hemolytic, antibacterial, and signaling activities are separable activities, and showed that CylLS” is precisely honed to maintain a balance between activity against eukaryotic cells and suicidal production due to increased bacteriocin activity, and/or indirectly due to increased production from greater signaling capacity.

Just prior to beginning his postdoctoral training in the Department of Pharmaceutical Sciences at OUHSC, Cobun’s postdoctoral mentor, Dr. Nathan Shankar, identified a pathogenicity island (PAI) in a hospital ward outbreak strain of E. faecalis. This PAI was shown to possess genes encoding a number of well-characterized E. faecalis virulence factors, as well as genes that have been hypothesized to be advantageous in GI tract colonization. While in his lab, Coburn demonstrated that the PAI is enriched among virulent, infection-derived isolates of E. faecalis, and that portions of the PAI can be mobilized and transferred both in vitro and during transient colonization of the GI tract (2). Further, he secured funding from the American Heart Association to explore the role of a new member of the AraC-type transcriptional regulators encoded on the PAI, designated PerA, in E. faecalis pathogenesis. In that study, Coburn’s major goal was to determine whether PerA contributes directly to causing disease and to identify genes, that also might be involved in disease, that are controlled by this protein. His findings were published in Infection and Immunity and PLoS One (3,4). During this period, he expanded his repertoire of molecular and biochemical techniques such as protein purification, gel-shift and DNase footprinting assays for promoter mapping, gene expression profiling by microarray analysis, and a murine intraperitoneal model of E. faecalis infection.

After successfully completing this training period, Coburn decided it was time for a major shift in his career goals and to pursue another area of research. After working in the area of bacterial genetics and molecular biology for 14 years, the prospect of undertaking new challenges and developing additional skills and capabilities was an exciting one, particularly the opportunity to work with a leader in the field of pathogenesis and chemotherapy of bacterial ocular infections, Michelle Callegan. As a postdoctoral fellow in Dr. Callegan’s laboratory, he explored the influence of changes in vascular permeability within the eye during the development of diabetes on the occurrence of endogenous bacterial endophthalmitis (EBE) in a mouse model of streptozotocin-induced diabetes that he helped develop. Using this model, Coburn demonstrated a correlation between the duration of diabetes and incidence of Klebsiella pneumoniae EBE and also showed that increases in vascular permeability within the eye may contribute to the enhanced rate of K. pneumoniae EBE (5).

In the summer of 2011, Coburn secured a faculty appointment in the Department of Ophthalmology at OUHSC. He began developing his own research program that is primarily focused on identifying mechanisms by which Enterococcus faecalis causes ocular infections, exploring the pathogenic mechanisms of S. aureus and K. pneumoniae EBE, and evaluating the effectiveness of a novel biomimetic nanosponge as an adjunct therapy for detoxification of ocular infections caused by pathogens that produce pore-forming toxins.