Date of Award

8-2007

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Microbiology

Advisor

Tzeng, Jeremy

Committee Member

Lee , Burtrand

Committee Member

Temesvari , Lesly

Committee Member

Luo , Pengju

Abstract

Staphylococcus aureus (S. aureus), a major human pathogen, is a common cause of infections worldwide due to its high virulence intensity. By adapting to rapidly changing and uniformly hostile environments, strains of S. aureus acquire resistance to antimicrobial agents shortly after their exposure. For example, within a year of its introduction, S. aureus developed resistance to methicillin which triggered the development of other antimicrobial treatments. In spite of the various antibiotics currently used to treat methicillin-resistant S. aureus (MRSA) infections, antimicrobial resistance is an unavoidable consequence due to the selective pressure of antibiotic exposure. Thus, other prevention modalities are warranted to prevent MRSA transmission.
Titanium dioxide (TiO2) nanoparticles decompose organic compounds by the formation and constant release of hydroxyl radicals and superoxide ions when exposed to non-lethal ultraviolet (UV) light of 365nm at 370µw/cm2. Commercially available anatase phase TiO2 nanoparticles can serve as antimicrobial agents via UV light activation. However, brookite phase nanoparticles, due to their smaller particle size, may increase the efficiency of TiO2 nanoparticles to inhibit bacterial growth by promoting a greater surface area contact ratio which subsequently causes cell death in less time than anatase phase nanoparticles.
Both the TiO2-free suspension and drop-coated slide bioassays were conducted to determine the effects of UV light activated TiO2 nanoparticles on gram-negative, Escherichia coli, and gram-positive, S. aureus, cells and the results revealed non-selective killing properties of the nanoparticles. Furthermore, UV light activated brookite nanoparticles (1mg/mL) caused a 100% reduction in MRSA cell growth within 30 minutes while anatase nanoparticles, under the same conditions, required approximately 75 minutes for such complete cell death. Additionally, physical damage to the cells by UV light activated TiO2 nanoparticles was confirmed by scanning electron microscopy images.
Due to MRSA's ability to acquire resistance to antibiotics, these agents remain a temporary solution for the treatment of such pathogenic infections. In contrast, brookite phase TiO2 nanoparticles offer promise for the prevention of MRSA due to their physical, non-selective inhibitory effects on cells. Additionally, the utilization of TiO2 nanoparticles, as a means to prevent transmission could further reduce the emergence of multiple drug-resistant bacteria.
The long term goal of this research is to develop visible light activated surface coatings of TiO2 nanoparticles that could be used in clinical settings to reduce the transmission of bacterial infections. Therefore, visible light activation of brookite nanoparticles for practical usage was also evaluated.

Included in

Microbiology Commons

Share

COinS