Staphylococcus aureus is a Gram positive coccoid shaped bacterium that is a normal inhabitant of the human skin microbiome and nasal passages. S. aureus can cause a plethora of diseases ranging from skin and soft tissue infections to osteomyelitis and toxic shock syndrome. Outside of the average difficulty treating S. aureus infections, the ability of S. aureus to resist antibiotic treatment further increases the clinical challenges, Methicillin-resistant S. aureus is extremely difficult to clear. Another of the difficulties of treating S. aureus infections lies in its ability to colonize a huge variety of host tissues because of its versatile metabolism. S. aureus has a branched respiratory chain, meaning it has more than one way to generate energy. If energy generation is interrupted completely, the bacterium would not be able to complete basic cellular functions resulting in cell death. Taking advantage of these pathways for treatment is an extremely difficult task because S. aureus can switch to fermentative metabolism adds an extra energy generating pathway. As it stands, there are two phenotypes of S. aureus a drug or drug cocktail must be able to inhibit or kill, fully functional respiring S. aureus and fully respiration-arrested (fermenting) S. aureus. In the clinic, aminoglycoside antibiotics have been used to treat S. aureus infections, notably these antibiotic treatments shift bacterial metabolism into a fermentative state, S. aureus mutants that can only generate energy using fermentation can be isolated from patients treated with aminoglycosides. We hypothesize that targeting pathways that support fermentative metabolism can lead to total eradication of S. aureus infection. Chapter 1 will assess the clinical burden caused by S. aureus giving an in-depth review of the genetic and physiological components that contribute to successful infection.Chapter 2 describes the results of a small molecule screen using the GSK PKIS kinase inhibitor compound library and a novel terpenoid extract library against a menaquinone-deficient strain of S. aureus locked in a fermenting state. This screen identified 4 compounds that uniquely inhibit fermenting S. aureus growth and several compounds that promote growth in a Wild Type strain. Another important factor of this screen is that it was performed in the Je2 background, a USA300 strain similar to the current endemic stain. While growth promotion of a dangerous strain is not the ideal outcome of a small molecule inhibiting screen, this phenotype can still help identify crucial pathways beneficial to the growth of S. aureus and identifying these pathways can lead to better drug development in the near future. Chapter 3 discusses a potential ‘druggable’ target of S. aureus, the cellular membrane. While unsaturated fatty acids have been observed to have modest anti-staphylococcal activity on respiring S. aureus, saturated fatty acids have been shown to be largely ineffective in inhibiting staphylococcal proliferation. These studies show that a range of saturated fatty acids specifically inhibits respiration-arrested bacterial cells. A thorough investigation of the mechanism by which this inhibition occurs is described in this chapter. Chapter 4 summarizes the findings and implications of this dissertation. Reflecting on the discoveries herein, discussing the results and the potential use of these data. This chapter provides future directions of this research and the impacts this work has on the field of microbiology, specifically in treating S. aureus in the clinic. In all, this dissertation reveals several novel findings that can lead directly to positive clinical outcomes.
Read
