Characterization of Staphylococcus epidermidis and Candida albicans Biofilms
Creators: name: Beckwith, Joanne
Publisher: name: My University
Year: 2021
Subjects: subject: Biofilms
subject: Engineering Education Research
subject: Staphylococcus epidermidis
subject: Candida albicans
subject: Rheology
subject: Chemical Engineering
subject: FOS: Chemical engineering
subject: Engineering

description: This dissertation investigates factors that affect the structural and rheological properties of bacterial and fungal biofilms while also presenting a qualitative study of the experience of undergraduates with rural backgrounds in engineering. Biofilms, frequently responsible for clinical infections, are structured communities of cells encapsulated in an extracellular matrix. We explore these biofilms from a mechanical, material perspective. The accompanying study of rural undergraduates addresses a gap in understanding their experiences of barriers and motivations for pursuing a degree in engineering. First, we examine the effect of heated perfusate on Staphylococcus epidermidis biofilms. An in vitro flow cell system was used to grow biofilms under flow conditions. Biofilms were exposed to elevated temperatures. Surface adhered biofilms and disseminated materials were characterized for viability and structure. Surface adhered biofilms showed a 4-fold decrease in viability, and Fast Fourier transform analysis showed increased heterogeneity with increasing temperature. Using optical density, we showed an increase in dissemination with increasing temperature, and all disseminated material was viable. However, when antibiotics were added, disseminated biofilms were killed completely. Next, we apply our findings in vivo. Central venous catheters were inserted into rats and infected with S. epidermidis. The catheters were exposed to heat treatment by oscillatory perfusate. We found a 2-log decrease in biomass on the catheter surface with oscillation. A computational model estimated the temperatures that could not be measured. There was a 6°C difference between the catheter inlet. The computational model also gave insight into thermal injury and will aid in the determination of a therapeutic window for future studies. Chapter four begins to bridge the gap between well-characterized bacterial biofilm systems and the emerging field of fungal biofilms. We developed a protocol allowing for biofilm growth conducive to testing by parallel plate rheometry. We ensured the appropriateness of the method by testing for factors that often impact rheological measurement. We found that Candida albicans biofilms were viscoelastic materials. The yield stress, measured by a strain amplitude sweep, was approximately 850 Pa. We also investigated fungal biofilm structure using microscopy and image analysis. Finally, we used our method to characterize biofilms made from chitin synthase mutant strains. Developing these rheological and structural characterization tools is a critical step to resolving differences in fungal biofilms due to genetic and phenotypic variability. Chapters two through four add to the understanding of biofilm dissemination and rheological properties. Insight into biofilm properties aids in the development of control strategies and theoretical models of biofilms. In turn, this work aims to reduce the disease burden of biofilms in medical device infections. In chapter five we present an engineering education research study. Guided by narrative inquiry, Tinto’s theory of student attrition, and self-determination theory, we present the motivations rural students cite and the barriers faced when starting an engineering program. Rural students cited five themes as barriers to pursuing engineering: limited exposure to engineering, lack of institutional support, perceptions of being underprepared, adapting to living in a city, and perceived social differences with peers. Motivations were categorized into four areas: motivations to attend college, to pursue engineering, to attend the specific research institution, and to leave or return home post-graduation. By understanding the experiences of rural students, educators can help them navigate the educational system and find their place in an engineering community of practice.