Theses and Dissertations
This collection includes both ASU Theses and Dissertations, submitted by graduate students, and the Barrett, Honors College theses submitted by undergraduate students.
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- Creators: Haydel, Shelley
Description
The prevalence of antibiotic resistant bacterial pathogens has increased since the introduction of penicillin in the 1940s. Insufficient development of novel antibacterial agents is leaving us with a failing arsenal of therapies to combat these pathogenic organisms. We have identified a clay mineral mixture (designated CB) that exhibits in vitro antibacterial activity against a broad spectrum of bacterial pathogens, yet the antibacterial mechanism of action remains unknown. Antibacterial susceptibility testing of four different clay samples collected from the same source revealed that these natural clays had markedly different antibacterial activity. X-ray diffraction analyses of these minerals revealed minor mineralogical differences across the samples; however, ICP analyses demonstrated that the concentrations of many elements, Fe, Co, Cu, Ni, and Zn in particular, vary greatly across the four clay mixture leachates. Supplementation of a non-antibacterial leachate containing lower concentrations of Fe, Co, Ni, Cu, and Zn to final ion concentrations and a pH equivalent to that of the antibacterial leachate resulted in antibacterial activity against E. coli and MRSA, confirming the role of these ions in the in vitro antibacterial clay mixture leachates. The prevailing hypothesis is that metal ions participate in redox cycling and produce ROS, leading to oxidative damage to macromolecules and resulting in cellular death. However, E. coli cells showed no increase in DNA or protein oxidative lesions and a slight increase in lipid peroxidation following exposure to CB-L. Supplementation of CB-L with ROS scavengers eliminated oxidative damage in E. coli, but did not rescue the cells from killing, indicating that in vitro killing is due to direct metal toxicity and not to indirect oxidative damage. Finally, we ion-exchanged non-antibacterial clays with Fe, Co, Cu, and Zn and established antibacterial activity in these samples. Treatment of MRSA skin infections with both natural and ion-exchanged clays significantly decreased the bacterial load after 7 days of treatment. We conclude that 1) in vitro clay-mediated killing is due to toxicity associated directly with released metal ions and not to indirect oxidative damage and 2) that in vivo killing is due to the physical properties of the clays rather than metal ion toxicity.
ContributorsOtto, Caitin Carol (Author) / Haydel, Shelley (Thesis advisor) / Stout, Valerie (Committee member) / Roberson, Robby (Committee member) / Sandrin, Todd (Committee member) / Rege, Kaushal (Committee member) / Arizona State University (Publisher)
Created2014
Description
This study examines the effect of the translation of traditional scientific vocabulary into plain English, a process referred to as Anglicization, on student learning in the context of introductory microbiology instruction. Data from Anglicized and Classical-vocabulary lab sections were collected. Data included exam scores as well as pre and post-course surveys on reasoning skills, impressions of biology, science and the course, and microbiology knowledge. Students subjected to Anglicized instruction performed significantly better on exams that assessed their abilities to apply and analyze knowledge from the course, and gained similar amounts of knowledge during the course when compared to peers instructed with standard vocabulary. Their performance in upper-level courses was also better than that of their traditionally educated peers. Hypotheses related to the effect are presented and evaluated; implications for instruction are discussed.
ContributorsRichter, Emily (Author) / Lawson, Anton (Thesis advisor) / Stout, Valerie (Committee member) / Haydel, Shelley (Committee member) / Atkinson, Robert (Committee member) / Arizona State University (Publisher)
Created2011
Description
This study was conducted as part of an underlying initiative to elucidate the mechanism of action of natural antibacterial clay minerals for application as therapeutic agents for difficult-to-treat infections such as methicillin-resistant Staphylococcus aureus (MRSA)-derived skin lesions and Buruli ulcer. The goal of this investigation was to determine whether exposure to the leachate of an antibacterial clay mineral, designated as CB, produced DNA double-strand breaks (DSBs) in Escherichia coli. A neutral comet assay for bacterial cells was adapted to assess DSB levels upon exposure to soluble antimicrobial compounds. Challenges involved with the adaptation process included comet visualization and data collection. To appropriately account for antimicrobial-mediated strand fragmentation, suitable control reactions comprised of exposures to water, ethanol, kanamycin, and bleomycin were developed and optimized for the assay. Bacterial exposure to CB resulted in significantly longer comet lengths compared to negative control exposures, suggesting that CB killing activity involves the induction of DNA DSBs. The results of this investigation further characterize the antimicrobial mechanisms associated with a particular clay mineral mixture. The adapted comet assay protocol described herein functions as an effective tool to assess double-strand fragmentation resulting from exposure to soluble antimicrobial compounds and to visually compare results from experimental and control reactions.
ContributorsSolanky, Dipesh (Author) / Haydel, Shelley (Thesis director) / Stout, Valerie (Committee member) / Adusumilli, Sarojini (Committee member) / Barrett, The Honors College (Contributor) / College of Liberal Arts and Sciences (Contributor)
Created2012-12
Description
The spread of antibiotic resistant bacteria is currently a pressing global health concern, especially considering the prevalence of multi-drug resistance. Efflux pumps, bacterial machinery involved in various active transport functions, are capable of removing a broad range of antibiotics from the periplasmic space and the outer leaflet of the inner membrane, frequently conferring multi-drug resistance. Many aspects of efflux machinery’s structure, functions, and inter-protein interactions are still not fully understood; further characterization of these components of efflux will provide a strong foundation for combating this resistance mechanism. In this project, I further characterize the channel protein TolC as a part of the AcrAB-TolC efflux pump complex in Escherichia coli by first determining the specificity of compensatory mutations in TolC against defective AcrA and AcrB, and then identifying TolC residues that might influence TolC aperture dynamics or stability when altered. Specificity of compensatory mutations was determined using an array of TolC mutants, previously generated from defective AcrA or AcrB, against a different mutant AcrB protein; these new mutant combinations were then analyzed by real-time efflux and antibiotic susceptibility assays. A vancomycin susceptible TolC mutant—a phenotype that has been associated with constitutively open TolC channels—was then used to generate vancomycin-resistant revertants which were evaluated with DNA sequencing, protein quantification by Western blots, and real-time efflux assays to identify residues important for TolC aperture dynamics and protein stability and complex activity. Mutations identified in revertant strains corresponded to residues located in the lower half of the periplasmic domain of TolC; generally, these revertants had poorer efflux than wild-type TolC in the mutant AcrB background, and all revertants had poorer efflux activity than the parental mutant strain.
ContributorsMcFeely, Megan Elizabeth (Author) / Misra, Rajeev (Thesis director) / Haydel, Shelley (Committee member) / Stout, Valerie (Committee member) / School of Mathematical and Statistical Sciences (Contributor) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05