Date of Award

Spring 1-1-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Karl Linden

Second Advisor

Roberto Rodriguez

Third Advisor

Fernando Rosario-Ortiz

Abstract

Medium-pressure (MP) ultraviolet (UV) lamps are becoming a popular technology for UV disinfection. They have demonstrated significant advantages over conventional low-pressure (LP) UV lamps including markedly increased inactivation efficiency for adenovirus, which is considered the most UV resistant pathogen. MP UV lamps produce a polychromatic emission throughout the UV spectrum compared to the monochromatic emission at 253.7 nm produced by LP UV lamps. With increased use of MP UV lamps comes a need to better understand the technology for regulatory and optimization purposes.

This research aims to increase the understanding of microbial inactivation and cellular damage resulting from polychromatic UV emission. It focuses on UV-induced damage resulting from single-wavelength exposures either alone or sequentially. DNA damage induced by UV light in the upper end of the UV-C spectrum, ~280 nm, has been shown to be directly reversible through subsequent irradiation at lower wavelengths, ~230-240 nm. Polychromatic emission allows for the possibility that DNA will be exposed to multiple wavelengths throughout the UV-C spectrum; therefore, there exists the possibility that some UV-induced damage may be inadvertently reversed during MP UV irradiation. It is important to know whether typical MP UV doses emit enough low-wavelength radiation to effectively reverse DNA damage as the technology would not be fully optimized if damage reversal is occurring. This was studied using culture techniques to examine cell viability and a quantitative polymerase chain reaction (qPCR) to assess DNA damage. Multiple-wavelength exposures resulted in higher inactivation levels than single-wavelength exposures when using culture techniques for bacterial growth. However, DNA damage investigated through qPCR assays showed a significant decrease for samples subjected to multiple-wavelengths in sequence.

Single wavelength exposures were also used to investigate the causes for adenoviral resistance to LP UV irradiation and susceptibility to MP UV exposure. The mechanism responsible for increased inactivation efficiency by MP sources was studied through examining adenoviral protein damage resulting from single-wavelength exposures throughout the UV-C spectrum. This work helps to elucidate why MP UV lamps are so much more effective against adenovirus and also helps to understand the adenoviral mechanism responsible for its extreme resistance to LP UV irradiation. Protein damage was studied using sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE) as a means to separate and subsequently quantify protein presence. Initial results show significant protein damage at lower wavelengths, less than 230 nm, compared to the higher wavelengths in the UV-C spectrum.

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