EFFECTS OF HYPERBARIC OXYGEN ON STAPYLOCOCCUS AUREUS

Author

Alyssa Philips, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2018

Degree Name

Master of Science

Department

Molecular Biology Microbiology and Biochemistry

First Advisor

Olson, Michael

Abstract

Hyperbaric Oxygen Therapy (HBOT) is an old technology which has acquired value in chronic wound care. HBOT is known to promote local and systemic healing effects by improving the oxygenation of the wound tissue. The increased tissue oxygenation hastens removal of the bacterial bioburden, which allows resolution of inflammation and facilitates matrix production, cell division, and ultimately wound closure. Staphylococcus aureus is the most frequently isolated organism from Diabetic Foot Infections (DFI). Therefore, our lab chose to use the treatment paradigm of HBOT to initially look at the single species level as to how HBOT affects S. aureus. DFI are primarily polymicrobial, so the responses of bacterial communities to this therapy were also considered. Previous research focused solely on host response to HBOT, but our pilot testing indicates that HBOT also exhibits a bacterial response. Initial testing with S. aureus indicated that HBOT can create growth defects in bacteria in vitro. In preliminary experiments, our lab discovered that bacterial culture on solid medium is greatly altered under the pressure of hyperbaric oxygen. Normal robust growth and pigmentation are seen in S. aureus cultured in ambient conditions. However, when the same strain is cultured under HBOT conditions, there is a marked decrease in pigmentation and colony size. When other species were exposed to HBOT conditions, growth on solid media was significantly diminished. Interestingly, K. pneumoniae is able to grow normally under HBOT conditions. Normal air mixtures at the increased pressure do not have any discernable effect on bacterial growth, and the limiting effects of oxygen are not seen unless used at the increased pressure. In a broth macrodilution MIC assay, various antibiotics show an increase in susceptibility after exposure to HBOT. Lastly, biofilm formation is altered under HBOT conditions, further supporting a bacterial adjustment to HBOT and an altered mode of growth. In order to better understand the effects of a high pressure high oxygen environment on the bacterial bioburden, this study investigates the effects of HBOT on bacterial species comprising a chronic wound. Primary data has suggested that HBOT increases susceptibility of antibiotics, and can alter bacterial transcription to hinder growth of many organisms. We hypothesize that Hyperbaric Oxygen Therapy affects diabetic foot infections by changing the healing process via transcriptional alteration of bacterial species in the wound. Furthermore, we hypothesize that HBOT alters the efficacy of some antibiotics as well as affecting the biofilm capacity of many bacterial species.